Scalar Fields as Dark Matter in Spiral Galaxies

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暗物质成品

What is dark matter?
About 65 years ago, the first time that evidence of the existence of dark matter. At that time, Fulizizha Popovich found a large cluster of galaxies in the galaxy has a very high velocity, unless the quality of galaxy clusters is based on the number of calculations in which stars are more than 100 times the value, or cluster of galaxies can not bound lives of these galaxies. After decades of observation and analysis confirmed this. Although the nature of dark matter is still unknown, but by 80 years, accounting for about 20% of the energy density of dark matter to be widely accepted.
What is dark matter?
now we know that dark matter has become an important part of the universe. The total mass of dark matter is ordinary matter, 6.3 times the energy density in the universe, accounting for 1 / 4, but also important is that dark matter dominated the formation of cosmic structures. Now the nature of dark matter remains a mystery, but assuming it is a weak interaction of subatomic particles, then the resulting large-scale structure of the universe is consistent with the observations. Recently, however, the structure of galaxies and galaxy subanalysis shows that this assumption and the difference between observations, which at the same time provide a variety of possible dark matter theory was useless. Small-scale structure through the density, distribution, evolution and its environment studies can distinguish between these potential dark matter model for the nature of dark matter to bring a new dawn.

暗物质_中学教育-中考

Dark Matter暗物质There is perhaps no current problem of greater importance to astrophysics and cosmology than that of 'dark matter'.也许再没有比‘暗物质'对天体物理学和宇宙论而言是现在更为重要的问题了。

The controversy, as the name implies, is centered around the notion that there may exist an enormous amount of matter in the Universe which cannot be detected from the light which it emits.争论,如名字暗示的那样,争论的焦点集中在宇宙可能存在不能够从它发出的光被探测到的一种巨大量的物质。

This is 'matter' which cannot be seen directly. So what makes us think that it exists at all? Its presence is inferred indirectly from the motions of astronomical objects, specifically stellar, galactic, and galaxy cluster/supercluster observations.这是不能够被直接看到的‘物质'。

因此使我们认为它究竟存在与否?它的存在是从天文学物体运动确定的恒星，银河及银河星团/超星系观察被间接的推断出来。

The basic principle is that if we measure velocities in some region, then there has to be enough mass there for gravity to stop all the objects flying apart. When such velocity measurements are done on large scales, it turns out that the amount of inferred mass is much more than can be explained by the luminous stuff. Hence we infer that there is dark matter in the Universe. There are many different pieces of evidence on different scales. And on the very largest scales, there may be enough to "close" the Universe, so that it will ultimately re-collapse in a Big Crunch.基本的原则是如果我们在一些地方测量速度,那么在那里必须有阻止所有物体飞离所需引力足够大的质量存在。

Investigating the Nature of Dark Matter

Investigating the Nature of DarkMatterThe phrase “dark matter” has become a buzzword in modern astrophysics as well as popular culture, and yet we still know very little about what dark matter really is. It is a mysterious substance that makes up 27% of the universe and that cannot be observed directly, but can only be inferred from the gravitational effects it has on visible matter. Therefore, dark matter is a topic of intense research and debate in the scientific community. In this article, we will explore the key aspects of dark matter and the different ways scientists are working to uncover its nature.What is Dark Matter?As mentioned, dark matter is a substance that does not emit, absorb or reflect light, hence its name. It does not interact strongly with electromagnetic forces, but it does with gravity, which is why its presence can be inferred from the gravitational effects it has on visible matter. One of the most well-known examples of this is the rotation curve of spiral galaxies. According to the laws of classical mechanics, the velocity of stars and gas in a galaxy should decrease as one moves away from the center, as the gravitational attraction of the visible matter decreases. However, observations have shown that the velocity remains constant or even increases, suggesting that there is an invisible mass that is causing this anomaly. This invisible mass is the dark matter.Another piece of evidence for the existence of dark matter is the distribution of matter in the universe as revealed by the cosmic microwave background radiation, which is the afterglow of the Big Bang. The pattern of temperature fluctuations in this radiation shows that the matter in the universe is not distributed evenly, but is rather clumped up in large structures such as galaxies and clusters of galaxies. However, this clumping up cannot be explained solely by the gravitational influence of visible matter; there must be an additional source of gravity, i.e. dark matter, to explain the observed distribution.Moreover, measurements of the large-scale structure of the universe, such as the distribution of galaxies and galaxy clusters, also point to the existence of dark matter.What is Dark Matter Made of?Despite its importance in shaping the structure of the universe, the identity of dark matter remains unknown. There are several hypotheses about what dark matter might be made of, but none of them has been conclusively proven yet. One popular hypothesis is that dark matter is composed of weakly interacting massive particles (WIMPs), which are hypothetical particles that would interact with normal matter only through the weak nuclear force and gravity. The idea is that WIMPs were produced in the early universe when it was hot and dense, and have been moving around freely ever since. If they collide with normal matter, they would transfer some of their energy and momentum, producing detectable signals. In fact, several experiments have been designed to detect WIMP interactions, such as the Large Underground Xenon (LUX) experiment and the Super Cryogenic Dark Matter Search (SuperCDMS).Another hypothesis is that dark matter is made of axions, which are theoretical particles that were originally proposed to explain a different problem in physics, the strong CP problem. The idea is that axions would be very light and weakly interacting, making them difficult to detect, but would still affect the motion of galaxies and other cosmic structures. The Axion Dark Matter eXperiment (ADMX) is currently searching for evidence of axions in a laboratory at the University of Washington.A third hypothesis is that dark matter is composed of primordial black holes, which are black holes that were formed by the collapse of a density fluctuation in the early universe. The idea is that these black holes could have a mass range that would make them more likely to be dark matter, and that their interactions with normal matter could produce observable effects. However, this hypothesis is less favored by most researchers, as the formation and stability of such black holes would require very specific conditions.ConclusionDespite decades of research, the nature of dark matter remains one of the most intriguing and elusive topics in astrophysics. It remains a theoretical construct that cannot be directly observed, but its effects on the motion and structure of the cosmos are undeniable. Researchers are continuing to study dark matter using a variety of tools and techniques, from telescopes that measure gravitational lensing to underground experiments that look for WIMP interactions. The hope is that someday we will finally be able to unravel the mystery of what dark matter is made of, and in doing so, gain a better understanding of the universe and our place in it.。

暗物质英语定义

暗物质英语定义Dark matter, also known as invisible matter, is a mysterious substance that makes up a significant portion of the universe. Although it cannot be directly observed, its existence is inferred from its gravitational effects on visible matter. In this article, we will explore the definition of dark matter, its properties, and its implications for our understanding of the cosmos.Dark matter is believed to account for approximately 85% of the total matter in the universe. Its presence is necessary to explain the observed rotational velocities of galaxies and the gravitational lensing effects observed in clusters of galaxies. Unlike ordinary matter, dark matter does not interact with electromagnetic radiation, making it invisible to telescopes and other instruments that rely on light detection.One of the key properties of dark matter is its non-baryonic nature. Baryonic matter, which includes protons and neutrons, makes up only a small fraction of the total matter in the universe. Dark matter, on the other hand, consists of particles that do not interact via the strong nuclear force, which binds protons and neutrons together. Instead, dark matter particles are thought to interact primarily through gravity and weak nuclear forces.The exact nature of dark matter remains unknown, but several theoretical candidates have been proposed. One possibility is that dark matter consists of weakly interacting massive particles (WIMPs). These hypothetical particles would have masses larger than those of ordinary matter particles and would interact only weakly with other particles. Another candidate is the axion, a hypothetical particle that could explain the absence of certain symmetry violations in the strong nuclear force.The search for dark matter is a major focus of modern astrophysics and particle physics. Scientists employ a variety of experimental techniques to detect or indirectly infer the presence of dark matter. These include direct detection experiments, which aim to detect the rare interactions between dark matter particles and ordinary matter, and indirect detection experiments, which look for the products of dark matter annihilation or decay.Understanding the nature of dark matter is crucial for our understanding of the universe's evolution and structure formation. The presence of dark matter has profound implications for the Big Bang theory and the formation of galaxies and galaxy clusters. It is believed that dark matter played a crucial role in the formation of the large-scale structure of the universe, acting as a gravitational seed for the formation of galaxies and galaxy clusters.In addition to its gravitational effects, dark matter also influences the distribution of ordinary matter. The presence of dark matter affects the growth of structures in the universe, leading to the formation of cosmic web-like structures composed of filaments and voids. These structures can be observed through large-scale surveys of galaxies and the cosmic microwave background radiation.In conclusion, dark matter is a mysterious substance that constitutes a significant portion of the universe. Although invisible and non-baryonic, its presence is inferred from its gravitational effects on visible matter. The search for dark matter is an active area of research, with scientists employing various experimental techniques to shed light on its nature. Understanding dark matter is crucial for our understanding of the universe's evolution and structure formation.。

宇宙暗物质dark_matter_intro讲解

Jupiter-size and above planets are a serious contender, and are called MACHOs by the community - MAssive Compact Halo Objects.
IDEA 2: Neutrinos Light, neutral particles of which at least some have a small mass. Produced in enormous numbers in stars and possibly at the big bang. If there are enough of them, they could (maybe) be the dark matter.
Star’s motion towards you, relative to the galactic centre alters wavelength of light
Need World’s largest telescope...
Some Results
This is what we expect....
(A alternative theory (MOND) has been seriously proposed, cannot yet rule this out)
Gravitational Lensing of Light Bending of light in gravitational fields can make lenses out of massive objects
Question:
Is the mass in the universe all observable through emmission or absorbsion of electromagnetic radiation ?

在攀枝花苏铁中发现导管

收稿日期:2006207212;修回日期:2006212230作者简介:黄荣(1961-),男,高级工程师,研究方向为园林植物学.通讯作者:吴俊.E 2mail :sjunwwu @文章编号:　049026756(2007)022*******在攀枝花苏铁中发现导管黄　荣1,吴　俊2(1.攀枝花市园林科学研究所,攀枝花617000;2.四川大学生命科学学院生物资源与生态环境教育部重点实验室,成都610064)摘　要:攀枝花苏铁的根、叶柄、羽片的木质部用乔菲氏液进行解离,在光学显微镜下观察,发现了形态各异的导管:有环纹导管、螺纹导管、梯纹导管、网纹导管和孔纹导管.关键词:攀枝花苏铁;根;叶柄;羽片;导管中图分类号:Q944 文献标识码:AV essels discovered in Cycas panzhi huaensis L.Zhou et S.Y.YangHUA N G Rong 1,W U J un2(1.Institute of G arden Science in Panzhi Hua City in Sichuan ,Panzhihua 617000,China ;2.K ey Laboratory of Bio 2resource and Eco 2environment of Ministry of Education ,College of Life Sciences ,Sichuan University ,Chengdu 610064,China )Abstract :Roots ,petioles and pinnas of Cycas panz hihuaensis were dissociated by the nitric acid 2chrome acid solution and observed in optical microscope.The various morpha vessels were discovered in the xylem of the root ,petiole and pinna such as annular vessels ,spiral vessels ,scalariform vessels ,reticulate vessels ,pitted vessels ,and so on.K ey w ords :Cycas panz hihuaensis ,root ,petiole ,pinna ,vessel1　引　言攀枝花苏铁Cycas Panz hihuaensis L.Zhou et S.Y.Yang 是我国特有种,仅分布于我国四川省攀西地区及与云南省交界的元谋等地,因此也是我省的国家级二级保护珍稀植物.它也是苏铁类中自然分布最北界的野生种群[1].苏铁类植物是裸子植物中最原始的类群,在系统演化上,裸子植物输导组织的木质部中只具有管胞,而不具有导管.管胞是绝大部分蕨类和裸子植物唯一输导水分的组织[2].1993年有研究者[3]曾在攀枝花苏铁的生物学特征研究中,在其叶柄中曾观察到有似导管的结构.近年来也有在苏铁类其他物种中发现导管的报道[4,5].在此基础上,我们对攀枝花苏铁的营养器官进行了进一步研究,拟为探讨苏铁类植物的系统演化积累有关形态学方面的资料.2　材料和方法从攀枝花市民政乡采集攀枝花苏铁的营养器官(根、叶柄、羽片)纵向切成薄片,分别用自来水煮沸多次,用乔菲氏液浸离7～10日[6].待材料充分解离后,去掉浸离液,自来水换洗多次至无黄棕色为止,系列脱水至无水乙醇,离心沉降,取出离析物,用Herr πs 液[7]透明,一至数日,制成临时装片,在Olympus 干涉差显微镜下观察,测量并摄影.2007年4月　第44卷第2期四川大学学报(自然科学版)Journal of Sichuan University (Natural Science Edition )　Apr.2007Vol.44　No.23　结　果在攀枝花苏铁的根、羽片、叶柄中均观察到不同类型的导管,如环纹导管、螺纹导管、梯纹导管、网纹导管和孔纹导管,其中网纹导管较多.这些导管大多数呈圆筒形,而且不同器官中导管分子的长宽比不一样.在根、叶柄和羽片中的导管分子的长宽之比分别为58195/34185μm ,129105/58163μm ,108140/36180μm.在各类型导管中,环纹和螺纹导管要细长,梯纹、网纹和孔纹导管较粗短,尤以孔纹导管分子近于等直径的筒状.导管分子的端壁有倾斜的,也有水平的,其穿孔板多为复穿孔板,单穿孔板罕见.有的纤细的导管分子具有向上突起的尾部(图1).图1　攀枝花苏铁中观察到的各类导管分子Fig.1　Different ressels obsrved in C.panz hihuaonsis(1)孔纹导管分子;(2)网纹导管分子,箭头所示导管的倾斜端壁;(3)孔纹导管分子,箭头所示倾斜至水平的端壁,具复穿孔板;(4)粗短的孔纹导管分子,箭头所示复穿孔板;(5)具有尾部(箭头所示)的长螺纹导管分子和短的网纹导管分子;(6)粗短的孔纹导管分子,箭头所示单穿孔板(1)The pitted vessel ;(2)The pitted vessel ,the arrow shows the acclivitous end 2wall of vessel ;(3)The pitted vessel ,the arrow shows the level end 2wall of vessel with compound perforation plate ;(4)The dumpy pitted vessel with compound perforation plate as the arrow shows ;(5)A long spiral vessel with a tail as the arrow shows and a short reticulated vessel ;(6)The dumpy pitted vessel with simple perforation plate as the arrow shows4　讨　论在被子植物中,管状分子的一些结构特征用来作为研究它们系统演化(进化)的基础.导管是木质部中最特化的细胞,是被子植物普遍具有的.它们是由许多长管状的,细胞壁次生木质化的,末端壁上具有穿孔的死细胞(导管分子)纵向连接而成的.在导管分子端壁上具穿孔的横壁即穿孔板.具有一个穿孔板的为单穿孔板,具有两个或两个以上穿孔的穿孔板为复穿孔板.复穿孔板或多或少是倾斜的,单穿孔板则常为水平的.在系统发育上,水平的单穿孔板是简单的,是进化的;而复穿孔板则是原始的性状[2,8-10].攀枝花苏铁的营养器官的木质部中虽具有不同类型的导管,但不论何种类型的导管,其导管分子多具倾斜的复穿孔板.即使是近于等直径的孔纹导管分子,其端壁已近于水平,但仍具有复穿孔板,偶见单穿孔板.因此参照上述论点,从导管的演化(进化)观点看,攀枝花苏铁营养134第2期黄荣等:在攀枝花苏铁中发现导管　器官中管状分子———导管是处于原始的状态.管状分子是植物从水平向陆生进化时产生的.这些管状分子的形态进化过程中,两种主要功能的趋势表现明显,一是结构的发展促进迅速的输导,另一方面是提高管状分子的强度以增加其支持力度.但是这两种趋势的发展是相互矛盾的.因此, Carlguist,Esau[8,11]先后提出了木质部进化的生态途径,即现存的植物的木质部中,结构上的差异是功能适应于不同生境的进化变化的结果.这种适应性变化是由于与各种植物类群有关的不同环境中选择压力的结果.众所周知,苏铁类植物是与恐龙同时代的物种,但它并没有随恐龙的灭绝而灭绝.我们能够想象这样一个古老的物种中包含了多么丰富的遗传信息.攀枝花苏铁是苏铁类中自然分布最北界(北纬26°36′～28°30′),数量最多(约23万株),面积最大(约300hm2)的野生种群.它经历了第三世纪的造山运动和第四世纪冰川时期,存活并繁衍至今,这是极罕见的.在它的营养器官的木质部中发现了不同类型的导管(虽其形态演化上仍处于原始状态)初步揭示了攀枝花苏铁能从各种自然灾害(地球的板块运动、火山爆发、干旱等)中存活并繁衍的原因,同时也表明它的输导功能已经适应了环境变化,相应促进其结构特化更趋于完善.结合攀枝花苏铁的有性生殖特征[12-15],我们能更深刻的理解它繁衍至今、数量众多的内因.这些研究无疑对苏铁类植物的系统演化(进化)具有重要科学价值.参考文献:[1]　管中天,周林.中国苏铁[M].成都:四川科学技术出版社,1996.[2]　李正理.植物解剖学[M].北京:科学出版社,1986.[3]　李平,吴先军,赵振琚,等.攀枝花苏铁(Cycas Panz hi2huaensis L.Zhou et S.Y.Y ang)的生物学特性研究—营养器官的形态解剖研究[J].四川大学学报:自然科学版,1994(4):546.[4]　黄玉源,张宏达.首次在苏铁类中发现导管[J].广西农业生物科学,1999,18(2):161.[5]　林鉴钊,黄玉源.在苏铁类植物中再次发现导管[J].广西农业生物科学,1999,18(3):233.[6]　郑国倡.生物显微技术[M].北京:人民教育出版社,1980.[7]　Herr J M J.A new clearing2squash technique for thestudy of ovule development in agiosperms[J].Amer JBot,1971,58(8):785.[8]　Fahn A.Plant anatomy[M].Oxford:Pergamon Press,1990.[9]　A.S.福斯特,E.M小吉福德.维管植物比较形态学[M].北京:科学出版社,1983.[10]　刘穆.种子植物形态解剖学导论[M].北京:科学出版社,2001.[11]　K.Esau.种子植物解剖学[M].上海:人民出版社,1989.[12]　李平,李旭锋,杜林方,等.攀枝花苏铁的生殖生物学特性研究—大孢子发生、受精前雌配子体和颈卵器发育[J].四川大学学报:自然科学版,1998(5):769.[13]　吴先军,李平,王乾,等.攀枝花苏铁(Cycas Panz hi2huaensis L.Zhou et S.Y.Y ang)的生殖生物学研究—授粉后雌、雄配子体发育研究[J].四川大学学报:自然科学版,1995,(2):63.[14]　吴先军,李平,王乾,等.攀枝花苏铁(Cycas Panz hi2huaensis L.Zhou et S.Y.Y ang)的生殖生物学研究—小孢子发生及花粉粒发育[J].四川大学学报:自然科学版,1995(2):69.[15]　吴先军,李平,黄荣.攀枝花苏铁(Cycas Panz hi2huaensis L.Zhou et S.Y.Y ang)受精作用及胚胎发生研究[J].四川大学学报:自然科学版,1998(6):1130.234四川大学学报(自然科学版)第44卷。

Possible Effects of Dark Energy on the Detection of Dark Matter Particles

a r X i v :h e p -p h /0503120v 1 14 M a r 2005Possible Eﬀects of Dark Energy on the Detection of Dark MatterParticlesPeihong Gu,1Xiao-Jun Bi,2Zhi-Hai Lin,1and Xinmin Zhang 11Institute of High Energy Physics,Chinese Academy of Sciences,P.O.Box 918-4,Beijing 100049,P.R.China2Key laboratory of particle astrophysics,Institute of High Energy Physics,Chinese Academy of Sciences,P.O.Box 918-3,Beijing 100049,P.R.China (Dated:February 2,2008)Abstract We study in this paper the possible inﬂuence of the dark energy on the detection of the dark matter particles.In models of dark energy described by a dynamical scalar ﬁeld such as the Quintessence,its interaction with the dark matter will cause the dark matter particles such as the neutralino vary as a function of space and time.Given a speciﬁc model of the Quintessence and its interaction in this paper we calculate numerically the corrections to the neutralino masses and the induced spectrum of the neutrinos from the annihilation of the neutralinos pairs in the core of the Sun.This study gives rise to a possibility of probing for dark energy in the experiments of detecting the dark matter particles.Recent observational data from supernovae(SN)Ia[1]and cosmic microwave background radiation(CMBR)[2]strongly support for the‘cosmic concordance’model,in which the Universe is spatiallyﬂat with4%baryon matter,23%of cold dark matter(DM)and 73%of dark energy(DE).The baryon matter is well described by the standard model of the particle physics,however the nature of the dark matter and the dark energy remains unknown.There have been many proposals in the literature for the dark matter candidates the-oretically.From the point of view of the particle physics,the leading candidates for cold dark matter are the axion and the neutralino.Various experiments in the search directly or indirectly for these dark matter particles are currently under way.Regarding dark energy,the simplest candidate seems to be a remnant small cosmological constant.However,many physicists are attracted by the idea that dark energy is due to a dynamical component,such as a canonical scalarﬁeld Q,named Quintessence[3].Being a dynamical component,the scalarﬁeld of the dark energy is expected to interact with the other matters[4].There are many discussions on the explicit couplings of quintessence to baryons,dark matter,photons and neutrinos.These interactions if exist will open up the possibilities of probing non-gravitationally for the dark energy.In this paper we consider the possible eﬀects of the dark energy models which interact with the dark matter in the detection of the dark matter particles.Speciﬁcally we will study the inﬂuence of the dark energy on the neutralino masses in the Sun,and then calculate the neutrino spectrum annihilated from the neutralino pairs in the core of the Sun.We start with a coupled system of the interacting dark energy and the dark matter with the Lagrangian generally given byL eff=L DM+Lφ+L int,(1)where L DM and Lφare the free Lagrangian for dark matter and dark energy and the inter-action part is given byL int=−12M2S(φ)S2−gχΛ∂µφ¯ψγµψ−g SΛφ∂µφ∂µS− g isuch as the neutralino to be the dark matter particle and focus on the interactions which aﬀect the dark matter particles via the mass terms.Being a function of the quintessence scalarφthe mass of the dark matter particle will vary during the evolution of the universe.As shown in Refs.[5,6,7]this helps solve the coincidence problem.Furthermore,this type of interactions will aﬀect the cosmic structure formation[8],and the power spectrum of CMB[9].In this paper we will present a new possible eﬀect of the interacting dark energy with the dark matter in the detection of the dark matter particles.There are in general two diﬀerent ways,direct and indirect,in the detections of the dark matter particles.The direct detection records the recoil energy of the detector nuclei when the dark matter particles scatter oﬀthem as they pass through the Earth and interact with the matter.The indirect detection observes the annihilation products by the dark matter particles.Obviously the expected detection rates depend on the mass of the dark matter particles.In the presence of the interaction the mass of the dark matter particle will vary as a function of time and also space,and consequently the dark energy will inﬂuence the detection.To determine the mass of neutralino as a function of space we need to know the value of the dark energy scalarﬁeld as a function of space.Taking into account the back reaction of the interaction between the dark matter and the dark energy the eﬀective potential of the dark energy scalar as a function of the energy density of the cold dark matterρχ(φ)is given byV eff=ρχ(φ)+V(φ).(3) For diﬀerent dark matter densities the values of dark energy scalarﬁeld are expected to be diﬀerent,and consequently the mass of dark matter particles will also be diﬀerent.For example,the mass of the dark matter particle in the center of the Milky Way could be diﬀerent from that in the halo near the solar system.Therefore,the gamma ray spectrum, or the synchrotron radiation spectrum,from the galactic center could be diﬀerent from that in the nearby halo.Especially for the neutralino dark matter particle its mass measured at the future linear collider(LC)or the large hadron collider(LHC)on the Earth may be diﬀerent from that measured in other places in the Milky Way,such as in the galactic center.Similarly,the spectrum of the dark matter radiation in the Milky Way might also be diﬀerent from other galaxies in the local group.In the following we will consider a speciﬁc model of the Quintessence and its interaction with the dark matter particle,the neutralino,and then study its eﬀects on the indirect detection via the process of the neutralinos annihilation into neutrinos.The dark energy potential which we take isV(φ)=V0eβφ/m p,(4) and the interaction between the dark energy and the dark matter particle are given byMχ(φ)=Mχ0 1+λχφ(y q¯Q L Hq R).(6)m pThe parameterλB above characterizing the strength of this type of interaction will be shown below to be strongly constrained.However,since the baryon density inside the Sun is much higher than any other matter densities,this interaction in Eq.(6)will be important to our study in this paper as well as that on the neutrino oscillations[14,17,18].The Eq.(5)shows that the mass of the dark matter particles varies during the evolution of the Universe.At the present time the mass of the neutralino dark matter particle is given by Eq.(5)with the scalarﬁeldφevaluated at the present timeφ0.This type of physics associated with the mass varying dark matter particles have been proposed and studied in the literature[6,9,19],but in these studies the masses of the dark matter particle are constant in space.In this paper we consider the case that neutralino masses vary as afunction of space,for instance the neutralino mass in the Sun diﬀers from that evaluated on the cosmological scale.The eﬀective potential of the dark energy scalar at the inner of the Sun or the Earth is given byV eff =ρB (φ)+ρχ(φ)+V (φ),(7)where ρB (φ)is the mass density of the baryon matter and ρχ(φ)=n χM χ(φ).Here it’s straightforward to obtain ρB (φ)=ρB 0−λB ρB 0φdφφ=φmin=0.(8)The contributions to the equation above from the dark matter and baryon are proportional to λB ρB and λχρχrespectively.Sincethe ρχis about 15orders of magnitude smaller than ρB in the core of the Sun [20],the inﬂuence of the dark matter on the eﬀective potential of the dark energy scalar can be safely ignored ifλB ≫λχρχβln λB ρBM cos χ=1+λχβV 0m p .(11)In Eq.(11)φ0is the cosmological value of the scalar ﬁeld at the present time.To satisfy the cosmological observations on the dark energy our numerical results show that φ0=−0.51m p ,V 0=4.2×10−47GeV 4and β=1and λχ=0.1which we have mentioned above.10-510-410-310-210-1100200300400500600700800900E µ(GeV)ΦµM χ=170GeV M χ=1TeVFIG.1:Spectra of the muons induced by the neutrinos from the annihilation of the neutralino dark matter particles in the core of the Sun with m χ=1TeV and in the cosmological scale with m χ=170GeV.The spectra are normalized at 10GeV and calculated by using the DarkSUSY package [23].The baryon energy density of the Sun ρ⊙B is about 2.5g/cm 3.However due to thelogarithm in Eq.(10),the eﬀect on the dark matter mass is insensitive to the baryon mass density ρB .For example,the baryon density in the Sun ρ⊙B is about a quarter of that inthe Earth,which causes that M ⊙χis about 2%smaller than the value at the Earth in ournumerical calculation for λB =10−9.The parameter λB is constrained by the tests on the gravitational inverse square law [21]and the tests on the equivalence principle [22]to be λB <∼O (10−2).Here we point out that the presence of the interaction of the dark energy with the baryon in Eq.(6)makes the baryon mass density also varyδρBρB =−λB βV 0.(12)If taking ρB (φmin )to be the baryon density in the Earth (which is similar to the baryon density of the Sun),δρB (φmin )indicates the correction of the dark energy to baryon mass in the Earth.The proton mass has been measured very precisely on the Earth with an error of 10−8.If we take as an example that δρB /ρB <10−8we obtain an upper limit on λB ,λB <10−9,which we use in the numerical calculation.Now we have φmin ≃49m p and consequently M ⊙χ/M cos χ≃6.In Fig.1we plot the muonspectra induced by the neutrino from the dark matter annihilation in the center of the Sun and in the cosmological scale.We choose the dark matter mass in the Sun to be1TeV, while the dark matter mass in the cosmological scale is about1TeV/6=170GeV.From the ﬁgure one can see clearly the diﬀerence in the neutrino spectra.On the cosmological scale the dark energy scalar is homogeneously distributed,however in this case it is inhomogeneous,which gives rise to energy densityρφin the Sun.From Eqs.(4)and(10)we haveρφρB =λB[4]See,for example,X.Zhang,Plenary talk at12th International Conference on Supersymmetryand Uniﬁcation of Fundamental Interactions(SUSY04),Tsukuba,Japan,17-23Jun2004, hep-ph/0410292,and references therein.[5] elli,M.Pietroni,and A.Riotto,Phys.Lett.B571,115(2003).[6]U.Franca and R.Rosenfeld,Phys.Rev.D69,063517(2004).[7]X.J.Bi,B.Feng,H.Li,and X.Zhang,hep-ph/0412002.[8]Adi Nusser,S.S.Gubser,and P.J.E.Peebles,astro-ph/0412586.[9]M.B.Hoﬀman,astro-ph/0307350.[10]P.Q.Hung,hep-ph/0010126.This paper is on the interaction between the quintessence andthe sterile neutrinos.[11]P.Gu,X.Wang,and X.Zhang,Phys.Rev.D68,087301(2003).[12]R.Fardon,A.E.Nelson,and N.Weiner,astro-ph/0309800.[13]P.Q.Hung and H.Pas,astro-ph/0311131.[14] D.B.Kaplan,A.E.Nelson,and N.Weiner,Phys.Rev.Lett.93,091801(2004).[15]R.D.Peccei,Phys.Rev.D71,023527(2005);Nucl.Phys.Proc.Suppl.137,277(2004).[16]X.Zhang,hep-ph/0410292;H.Li,Z.Dai,and X.Zhang,hep-ph/0411228.[17] E.I.Guendelman and A.B.Kaganovich,hep-th/0411188.[18]V.Barger,P.Huber,and D.Marfatia,hep-ph/0502196.[19]G.W.Anderson and S.M.Carroll,astro-ph/9711288;G.R.Farrar and P.J.E.Peebles,Astro-phys.J.604,1(2004).[20]G.Bertone,D.Hooper,and J.Silk,Phys.Rept.405,279(2005).[21] E.G.Adelberger,B.R.Heckel,and A.E.Nelson,Annu.Rev.Nucl.Part.Sci.53,77(2003).[22]Y.Su et.al.,Phys.Rev.D50,3614(1994);G.L.Smith et.al.,Phys.Rev.D61,022001(2000).[23]P.Gondolo et.al.,JCAP0407,008(2004).。

The mysteries of the universe Dark matter

The mysteries of the universe DarkmatterDark matter is one of the most enigmatic and perplexing concepts in the field of astrophysics and cosmology. It is a substance that makes up a significantportion of the universe, yet it remains largely elusive and mysterious to scientists. The existence of dark matter was first proposed in the 1930s by Swiss astronomer Fritz Zwicky, who observed that the visible matter in the Coma galaxy cluster could not account for the gravitational forces that were holding thecluster together. This led him to hypothesize the presence of unseen "dark" matter that was responsible for the gravitational effects. Since then, numerous observations and experiments have provided compelling evidence for the existenceof dark matter, but its true nature continues to elude researchers. One of the most compelling lines of evidence for dark matter comes from the study of the rotation curves of galaxies. When astronomers measure the velocities of stars and gas in a galaxy as a function of their distance from the galactic center, theyfind that the velocities do not decrease as expected with increasing distance. Instead, the velocities remain constant or even increase, indicating the presence of additional unseen mass that is providing the gravitational pull to keep thestars and gas in their orbits. This discrepancy between the observed motion of galactic objects and the visible matter in galaxies has led scientists to conclude that there must be a significant amount of dark matter present in galaxies, outweighing the visible matter by a factor of about six to one. Another piece of evidence for dark matter comes from the study of the large-scale structure of the universe. Observations of the cosmic microwave background radiation, the afterglow of the Big Bang, have revealed subtle patterns in the distribution of matter onthe largest scales. These patterns can be explained by the presence of dark matter, which exerts gravitational forces to shape the distribution of galaxies and galaxy clusters in the universe. Additionally, the gravitational lensing of distant galaxies by intervening mass concentrations, such as galaxy clusters, provides further evidence for the presence of dark matter. The bending of light from these distant galaxies can only be explained by the gravitational influence of unseenmass, which is consistent with the properties of dark matter. Despite the overwhelming evidence for the existence of dark matter, its true nature remains a profound mystery. Dark matter does not emit, absorb, or reflect light, making it invisible to telescopes and other instruments that rely on electromagnetic radiation for detection. This has made it incredibly challenging for scientists to directly observe and study dark matter, leading to a wide range of theoretical and experimental efforts to uncover its properties. One of the leading candidates for the identity of dark matter is a type of particle that interacts only weakly with ordinary matter and electromagnetic forces, known as a weakly interacting massive particle (WIMP). WIMPs are a theoretical class of particles that arise in extensions of the standard model of particle physics, and they are thought to have been produced in the early universe in sufficient quantities to account for the observed abundance of dark matter today. Numerous experiments around the world are dedicated to detecting WIMPs through their rare interactions with ordinary matter, such as through the recoil of atomic nuclei in underground detectors or the production of secondary particles in particle accelerators. Another potential explanation for dark matter is the existence of primordial black holes, which are hypothesized to have formed in the early universe from the gravitational collapse of overdense regions. These black holes would not emit significant amounts oflight or other radiation, making them difficult to detect directly. However, their gravitational influence on surrounding matter could betray their presence, and ongoing observational campaigns are searching for the signatures of primordial black holes in the universe. In addition to these particle-based and astrophysical explanations, some scientists have proposed modifications to the laws of gravity as an alternative to dark matter. These modified gravity theories seek to explain the observed gravitational effects in galaxies and galaxy clusters without invoking the presence of additional unseen mass. While these theories have had some success in reproducing certain observational data, they have yet to provide a comprehensive and consistent explanation for the full range of evidence for dark matter. The search for dark matter continues to be a vibrant and active area of research in astrophysics and particle physics. New generations of experiments are pushing the boundaries of sensitivity and precision in the huntfor dark matter particles, while astronomers are mapping the distribution ofmatter in the universe with ever-increasing detail. The discovery of dark matter would represent a profound breakthrough in our understanding of the fundamental constituents of the universe and the forces that govern its evolution. It would also have far-reaching implications for our understanding of the cosmos, from the formation of galaxies and galaxy clusters to the ultimate fate of the universe itself. The quest to unravel the mysteries of dark matter is not just ascientific endeavor, but also a deeply human one. It speaks to our innatecuriosity about the nature of the universe and our place within it. Therealization that the majority of the matter in the universe is invisible and fundamentally different from the matter we interact with on a daily basis is both humbling and awe-inspiring. It challenges our preconceived notions of the cosmos and forces us to confront the limits of our current understanding. The search for dark matter is a testament to the human spirit of exploration and discovery, as we strive to push the boundaries of knowledge and unlock the secrets of the universe. In conclusion, dark matter remains one of the most captivating and tantalizing mysteries in modern science. Its existence is supported by a wealth of observational evidence, yet its true nature continues to elude us. Whether it is composed of exotic particles, primordial black holes, or a modification of thelaws of gravity, the discovery of dark matter would revolutionize our understanding of the cosmos and our place within it. The ongoing quest to uncover the secrets of dark matter is a testament to the enduring human spirit ofcuriosity and exploration, as we continue to push the boundaries of knowledge and strive to unlock the mysteries of the universe.。

The Science of Dark Matter and Its Discovery

The Science of Dark Matter and ItsDiscoveryIntroductionDark matter is an elusive substance that makes up about 27% of the universe. It neither emits nor absorbs light, making it invisible to telescopes. Scientists have been studying dark matter for decades, and its discovery is considered one of the greatest mysteries of modern physics. In this article, we will delve into the science of dark matter, its properties, and the research that has led to its discovery.What is Dark Matter?Dark matter is a hypothetical substance that does not interact with light or any other form of electromagnetic radiation. It is invisible to telescopes, but its presence is inferred from its gravitational effects on objects that emit light. Dark matter is thought to be five times more abundant than visible matter, which is what stars, planets, and galaxies are made of.The Properties of Dark MatterAlthough scientists have yet to observe dark matter directly, they have been able to infer its properties from its gravitational effects. Dark matter is thought to be cold, meaning that its particles move relatively slowly. It is also believed to be non-interacting, meaning that it does not interact with other particles except through the force of gravity.Dark matter is widely thought to be made up of weakly interacting massive particles (WIMPs), which are particles that interact with each other only through the weak force and gravity. Other proposed candidates for dark matter particles include axions and sterile neutrinos, but these have not been observed directly.The Search for Dark MatterThe search for dark matter has been ongoing for several decades. One of the most promising methods for detecting dark matter involves looking for the energetic particles that result from the annihilation of dark matter particles. This method is called indirect detection and involves searching for gamma rays, neutrinos, or cosmic rays that are produced by the decay or annihilation of dark matter particles.Another way to detect dark matter is through the direct detection method, which involves looking for the recoil of atomic nuclei in a detector after they have been struck by dark matter particles. This method requires a sophisticated detector that can detect even the slightest signal. Several experiments are currently underway to detect dark matter particles using these methods.Discovery of Dark MatterThe discovery of dark matter can be traced back to the 1930s when Swiss astronomer Fritz Zwicky observed that the visible matter in the Coma cluster of galaxies was not enough to hold the cluster together. He hypothesized the presence of invisible matter that was holding the cluster together, which he called dark matter.Over the years, other scientists have provided evidence for the existence of dark matter. In the 1970s, Vera Rubin and Kent Ford studied the rotation curves of galaxies and found that the observed mass could not account for the observed rotation speeds. They concluded that there must be more mass in the form of dark matter that was holding the galaxies together.More recently, the European Space Agency’s Planck satellite produced a detailed map of the cosmic microwave background radiation, which is thought to be leftover radiation from the Big Bang. The map provided strong evidence for the existence of dark matter and its abundance in the universe.ConclusionThe discovery of dark matter is one of the most exciting and challenging areas of modern physics. Scientists continue to search for dark matter using a variety of methods, including indirect and direct detection. Although dark matter has yet to be observeddirectly, its presence and properties can be inferred from its gravitational effects on visible matter. As we continue to unravel the mysteries of dark matter, we are sure to gain new insights and a deeper understanding of the universe we inhabit.。

量子力学照亮前程英文

量子力学照亮前程英文英文回答：Quantum mechanics, the study of matter and energy at atomic and subatomic levels, has profoundly illuminated our understanding of the world and continues to shape our technological advancements.Quantum mechanics has revolutionized our comprehension of the fundamental nature of reality. It has revealed that particles, such as electrons and photons, can exhibit wave-like properties and that particles can exist in multiple states simultaneously. These insights have led to the development of new theories in physics, such as quantum field theory, which describes the interactions of particles at the subatomic level.The principles of quantum mechanics have also been applied to develop many transformative technologies that have revolutionized various fields. For example, the laser,which is based on the amplification of stimulated emission of radiation, has had a profound impact on diverse areas such as medicine, manufacturing, and communication.Quantum computers, which harness the principles of quantum mechanics to perform complex computations, hold immense potential for solving problems that are intractable for classical computers. These computers couldrevolutionize fields such as materials science, drug discovery, and cryptography.Quantum mechanics has also played a pivotal role in the development of advanced imaging techniques, such as magnetic resonance imaging (MRI) and positron emission tomography (PET). These techniques have revolutionized the diagnosis and treatment of diseases by providing detailed images of the body's internal structures.In addition, quantum mechanics has inspired the development of novel materials, such as graphene and topological insulators, which exhibit extraordinary electronic properties. These materials hold promise forapplications in electronics, energy storage, and computing.中文回答：量子力学，对原子和亚原子级别物质和能量的研究，深刻地阐明了我们对世界的理解，并持续塑造着我们的技术进步。

理解黑洞需要一定的想象力和科学知识英语

理解黑洞需要一定的想象力和科学知识英语Understanding Black Holes Requires a Certain Degree of Imagination and Scientific KnowledgeThe vastness of the universe is a constant source of fascination and wonder for human beings. As we gaze up at the night sky, our eyes are drawn to the twinkling stars, the enigmatic planets, and the mysterious celestial bodies that lie beyond our immediate reach. Among these cosmic enigmas, perhaps none have captured the public's imagination more than the phenomenon known as the black hole.Black holes are regions of space-time where the gravitational pull is so immense that nothing, not even light, can escape their grasp. These cosmic behemoths are the result of the collapse of massive stars at the end of their life cycle. When a star runs out of fuel, its core can no longer support the outward pressure that counteracts the inward pull of gravity, causing it to implode and form a singularity – a point in space-time where the laws of physics as we know them break down.Understanding the true nature of black holes requires a certaindegree of imagination and scientific knowledge. On the surface, the concept of a region of space-time where nothing can escape may seem straightforward, but the deeper one delves into the intricacies of black hole physics, the more complex and mind-bending the subject becomes.One of the key aspects of black holes that challenges our intuitive understanding is the concept of the event horizon. The event horizon is the point of no return – the boundary beyond which nothing, not even light, can escape the gravitational pull of the black hole. Visualizing this invisible barrier and comprehending its significance is a task that requires a significant amount of abstract reasoning.Imagine a person standing on the edge of a cliff, gazing out at the vast expanse of the ocean. As they look down, they can see the waves crashing against the rocks below, but they know that if they were to step over the edge, they would be unable to return. The event horizon of a black hole is analogous to this – it is the point at which the gravitational forces become so overwhelming that even the fastest-moving particles in the universe, photons of light, cannot escape.But the event horizon is just the tip of the iceberg when it comes to the complexities of black hole physics. As one delves deeper into the subject, the challenges to our understanding only grow moreprofound.Consider, for example, the concept of time dilation. According to Einstein's theory of general relativity, the passage of time is affected by the presence of strong gravitational fields. As an object approaches the event horizon of a black hole, the rate at which time passes for that object becomes increasingly slowed down relative to an observer outside the black hole. This means that from the perspective of an external observer, the object appears to be frozen in time, gradually becoming fainter and fainter as it crosses the event horizon.Visualizing this phenomenon requires a significant amount of imagination and a deep understanding of the principles of relativity. It challenges our everyday experience of time and forces us to consider the universe from a radically different perspective – one where the familiar laws of physics no longer apply in the same way.Another aspect of black holes that pushes the limits of our imagination is the nature of the singularity itself. At the center of a black hole, where all the matter and energy of the collapsed star is concentrated, the laws of physics as we know them break down completely. This point of infinite density and infinite curvature of space-time is known as the singularity, and it represents the ultimate limit of our current scientific understanding.Trying to comprehend the singularity, a region where the very fabric of space-time is torn apart, is a task that requires a leap of imagination that few can truly make. It forces us to confront the limitations of our own understanding and to grapple with the fundamental mysteries of the universe.Despite these challenges, the study of black holes has been a cornerstone of modern astrophysics and has led to numerous groundbreaking discoveries. Through the use of sophisticated telescopes and advanced mathematical models, scientists have been able to observe the behavior of black holes in unprecedented detail, shedding light on the most extreme and enigmatic phenomena in the cosmos.From the detection of gravitational waves, the ripples in the fabric of space-time caused by the collision of black holes, to the stunning images of the supermassive black hole at the center of the Milky Way, the study of black holes has pushed the boundaries of our scientific knowledge and our understanding of the universe.But perhaps the greatest contribution of the study of black holes is the way it has challenged our fundamental assumptions about the nature of reality. By confronting us with the limits of our own understanding, black holes have forced us to reckon with thepossibility that there are aspects of the universe that may forever remain beyond our grasp.In this sense, the study of black holes is not just a scientific endeavor, but a philosophical one as well. It reminds us that the universe is a vast and mysterious place, and that our knowledge, no matter how extensive, is always a work in progress. It challenges us to remain humble in the face of the unknown and to continue to explore the limits of our understanding with curiosity, wonder, and a willingness to adapt our perspectives as new evidence emerges.Ultimately, the study of black holes is a testament to the power of the human mind to grapple with the most complex and enigmatic phenomena in the universe. It requires a unique blend of imagination, scientific knowledge, and a willingness to embrace the unknown – qualities that have defined the pursuit of scientific discovery since the dawn of human civilization.。

Dark Matter Introduction

a rXiv:as tr o-ph/4245v12Fe b24INTRODUCTION Martin J Rees Institute of Astronomy,Madingley Road,Cambridge,CB30HA Abstract It is embarrassing that 95%of the universe is unaccounted for.Galax-ies and larger-scale cosmic structures are composed mainly of ‘dark mat-ter’whose nature is still unknown.Favoured candidates are weakly-interacting particles that have survived from the very early universe,but more exotic options cannot be excluded.(There are strong arguments that the dark matter is not composed of baryons).Intensive experimental searches are being made for the ‘dark’particles (which pervade our entire galaxy),but we have indirect clues to their nature too.Inferences from galactic dynamics and gravitational lensing allow astronomers to ‘map’the dark matter distribution;comparison with numerical simulations of galaxy formation can constrain (eg)the particle velocities and collision cross sections.And,of course,progress in understanding the extreme physics of the ultra-early universe could oﬀer clues to what particle might have existed then,and how many would have survived.The mean cosmic density of dark matter (plus baryons)is now pinned down to be only about 30%of the so-called critical density corresponding to a ‘ﬂat’universe.However,other recent evidence –microwave back-ground anisotropies,complemented by data on distant supernovae –re-veals that our universe actually is ‘ﬂat’,but that its dominant ingredient (about 70%of the total mass-energy)is something quite unexpected —‘dark energy’pervading all space,with negative pressure.We now con-front two mysteries:(i)Why does the universe have three quite distinct basic ingredients –baryons,dark matter and dark energy –in the proportions (roughly)5%,25%and 70%?(ii)What are the (almost certainly profound)implications of the ‘dark energy’for fundamental physics?1SOME HISTORYAstronomers have long known that galaxies and clusters would ﬂy apart unless they were held together by the gravitational pull of much more material than we actually see.The strength of the case built up gradually.The argument that clusters of galaxies would be unbound without dark matter dates back to Zwicky (1937)and others in the 1930s.Kahn and Woltjer (1959)pointed out that the motion of Andromeda towards us implied that there must be dark matter in our Local1Group of galaxies.But the dynamical evidence for massive halos(or‘coronae’) around individual galaxiesﬁrmed up rather later(e.g.Roberts and Rots1973, Rubin,Thonnard and Ford1978).Two1974papers were specially inﬂuential in the latter context.Here is a quote from each:The mass of galactic coronas exceeds the mass of populations ofknown stars by one order of magnitude,as do the eﬀective dimen-sions.....The mass/luminosity ratio rises to f=100for spiral andf=120for elliptical galaxies.With H=50km/sec/Mpc this ratiofor the Coma cluster is170(Einasto,Kaasik and Saar1974)Currently-available observations strongly indicate that the mass ofspiral galaxies increases almost linearly with radius to nearly1Mpc....and that the ratio of this mass to the light within the Holmberg ra-dios,f,is200(M/L⊙).(Ostriker,Peebles and Yahil,1974).The amount of dark matter,and how it is distributed,is now far better estab-lished than it was when those papers were written.The immense advances in delineated dark matter in clusters and in individual galaxies are manifest in the programme for this meeting.The rapid current progress stems from the con-ﬂuence of several new kinds of data within the same few-year interval:optical surveys of large areas and high redshifts,CMBﬂuctuation measurements,sharp X-ray images,and so forth.The progress has not been solely observational.Over the last20years,a com-pelling theoretical perspective for the emergence of cosmic structure has been developed.The expanding universe is unstable to the growth of structure,in the sense that regions that start oﬀvery slightly overdense have their expansion slowed by their excess gravity,and evolve into conspicuous density contrasts. According to this‘cold dark matter’(CDM)model,the present-day structure of galaxies and clusters is moulded by the gravitational aggregation of non-baryonic matter,which is an essential ingredient of the early universe(Pagels and Primack1982,Peebles1982,Blumenthal et al.1984,Davis et al.1985). These models have beenﬁrmed up by vastly improved simulations,rendered possible by burgeoning computer power.And astronomers can now compare these‘virtual universes’with the real one,not just at the present era but(by observing very distant objects)can probe back towards the formative stages when theﬁrst galaxies emerged.The following comments are intended to provide a context for the later papers. (For that reason,I do not give detailed references to the topics covered by other speakers–just some citations of historical interest).22THE CASE FOR DARK MATTER2.1BaryonsThe inventory of cosmic baryons is readily compiled.Stars and their remnants, and gas in galaxies,contribute no more than1%of the critical density(i.e.they giveΩb<0.01).However several percent more could be contributed by diﬀuse material pervading intergalactic space:warm gas(with kT≃0.1keV)in groups of galaxies and loose clusters,and cooler gas pervading intergalactic space that manifests itself via the‘picket fence’absorption lines in quasar spectra.(Rich clusters are rare,so their conspicuous gas content,at several KeV,is not directly signiﬁcant for the total inventory,despite its importance as a probe)These baryon estimates are concordant with those inferred by matching the He and D abundances at the birth of galaxies with the predicted outcome of nucle-osynthesis in the big bang,which is sensitive to the primordial baryon/photon ratio,and thus toΩb.The observational estimates haveﬁrmed up,with im-proved measurements of deuterium in high-z absorbing clouds.The bestﬁt occurs forΩb≃0.02h−2where h is the Hubble constant in units of100km s−1 Mpc−1.Observations favour h≃0.7.Ωb is now pinned down by a variety of argument to be0.04−0.05.This corre-sponds to only∼0.3baryons per cubic metre,a value so low that it leaves little scope for dark baryons.(It is therefore unsurprising that the MACHO/OGLE searches should have found that compact objects do not make a substantial contribution to the total mass of our own galactic halo.)2.2How much dark matter?An important recent development is thatΩDM can now be constrained to a value around0.25by several independent lines of evidence:(i)One of the most ingenious and convincing arguments comes from noting that baryonic matter in clusters–in galaxies,and in intracluster gas–amounts to 0.15−0.2of the inferred virial mass(White et al.1993).If clusters were a fair sample of the universe,this would then be essentially the same as the cosmic ratio of baryonic to total mass.Such an argument could not be applied to an individual galaxy,because baryons segregate towards the centre.However, there is no such segregation on the much larger scale of clusters:only a small correction is necessary to allow for baryons expelled during the cluster formation process.3(ii)Very distant galaxies appear distorted,owing to gravitational lensing by intervening galaxies and clusters.Detailed modelling of the mass-distributions needed to cause the observed distortions yields a similar estimate.This is a straight measurement ofΩDM which(unlike(i))does not involve assumptions aboutΩb,though it does depend on having an accurate measure of the clustering amplitude.(iii)Another argument is based on the way density contrasts grow during the cosmic expansion:in a low density universe,the expansion kinetic energy over-whelms gravity,and the growth of structure saturates at recent epochs.The existence of conspicuous clusters of galaxies with redshifts as large as z=1 is hard to reconcile with the rapid recent growth of structure that would be expected ifΩDM were unity.More generally,numerical simulations based on the cold dark matter(CDM)model model are a betterﬁt to the present-day structure for this value ofΩDM(partly because the initialﬂuctuation spectrum has too little long-wavelength power ifΩDM is unity).Other methods will soon oﬀer independent estimates.For instance,ΩDM can be estimated from the deviations from the Hubbleﬂow induced by large-scale irregularities in the mass distribution on supercluster scales.2.3What could the dark matter be?The dark matter is not primarily baryonic.The amount of deuterium calculated to emerge from the big bang would be far lower than observed if the average baryon density were∼2(rather than∼0.3)per cubic metre.Extra exotic par-ticles that do not participate in nuclear reactions,however,would not scupper the concordance.Beyond the negative statement that it is non-baryonic,the nature of the dark matter still eludes us.This key question may yield to a three-pronged attack: 1.Direct detection.Important recent measurements suggest that neutrinos have non-zero masses;this result has crucially important implications for physics beyond the standard model.The inferred neutrino masses seem,how-4ever,too low to be cosmologically important.If the masses and cross-sections of supersymmetric particles were known,it should be possible to predict how many survive,and their contribution toΩ,with the same conﬁdence with which we can compute the nuclear reactions that control primordial nucleosynthesis. Associated with such progress,we might expect a better understanding of how the baryon-antibaryon asymmetry arose,and the consequence forΩb.Optimists may hope for progress on still more exotic options.3.Simulations of galaxy formation and large-scale structureus that the temperatureﬂuctuations should be biggest on a particular length scale that is related to the distance a sound wave can travel in the early uni-verse.The angular scale corresponding to this length depends,however,on the geometry of the universe.If dark matter and baryons were all,we wouldn’t be in aﬂat universe–the geometry would be hyperbolic.Distant objects would look smaller than in aﬂat universe.In2001-02,measurements from balloons and from Antarctica pinned down the angular scale of this‘doppler peak’:the results indicated‘ﬂatness’–a result now conﬁrmed with greater precision by the WMAP satellite.A value of0.3forΩDM would imply(were there no other energy in the universe) an angle smaller by almost a factor of2–deﬁnitely in conﬂict with observations. So what’s the other70%?It is not dark matter but something that does not cluster–some energy latent in space.The simplest form of this idea goes back to 1917when Einstein introduced the cosmological constant,or lambda.A positive lambda can be interpreted,in the context of the ordinary Friedman equations, as aﬁxed positive energy density in all space.This leads to a repulsion because, according to Einstein’s equation,gravity depends on pressure as well as density, and vacuum energy has such a large negative pressure–tension–that the net eﬀect is repulsive.Einstein’s cosmological constant is just one of the options.A class of more general models is being explored(under names such as‘quintessence’)where the energy is time-dependent.Any form of dark energy must have negative pressure to be compatible with observations–unclustered relativistic particles, for instance,can be ruled out as candidates.The argument is straightforward: at present,dark energy dominates the universe–it amounts to around70% of the total mass-energy.But had it been equally dominant in the past,it would have inhibited the growth of the density contrasts in cosmic structures, which occurred gravitational instability.This is because the growth timescale for gravitational instability is∼(Gρc)−12when curvature is unimportant.Ifρtotal exceedsρc,the expansion is faster,so the growth is impeded.(Meszaros,1974)In the standard model,density contrasts in the dark matter grow by nearly 1000since recombination.If this growth had been suppressed,the existence of present-day clusters would therefore require irregularities that were already of substantial amplitude at the recombination epoch,contrary to the evidence from CMBﬂuctuations.For the‘dark energy’to be less dominant in the past,its density must depend on the scale factor R more slowly than the R−3dependence of pressure-free matter–i.e.its PdV work must be negative.Cosmologists have introduced a parameter w such that p=wρc2.A more detailed treatment yields the requirement that w<−0.5.This comes from taking account of baryons and dark matter,and requiring that dark energy should not have inhibited the6growth of structure so much that it destroyed the concordance between the CMBﬂuctuations(which measure the amplitude at recombination)and the present-day inhomogeneity.Note however that unless its value is-1(the special case of a classical cosmological constant)w will generally be time-dependent. In principle w(t)can be pinned down by measuring the Hubble expansion rate at diﬀerent redshiftsThis line of argument would in itself have led to a prediction of accelerating cosmic expansion.However,as it turned out,studies of the redshift versus the apparent brightness of distant SNIa–strongly suggestive if not yet completely compelling–had already conditioned us to the belief that galaxies are indeed dispersing at an accelerating rate.As often in science,a clear picture gradually builds up,but the order in which the bits of the jigsaw fall into place is a matter of accident or contingency.CMBﬂuctuations alone can now pin downΩDM and the curvature independent of all the other measurements.The‘modern’interest in the cosmological constant stems from its interpretation as a vacuum energy.This leads to the reverse problem:Why is lambda at least120powers of10smaller than its‘natural’value,even though the eﬀective vacuum density must have been very high in order to drive inﬂation.If lambda is fully resurrected,it will be a posthumous‘coup’for de Sitter.His model,dating from the1920s,not only describes inﬂation,but would then also describe future aeons of our cosmos with increasing accuracy.Only for the50-odd decades of logarithmic time between the end of inﬂation and the present would it need modiﬁcation!.But of course the dark energy could have a more complicated and time-dependent nature–though it must have negative pressure,and it must not participate in gravitational clustering.4SUMMARY AND PROSPECTSCosmologists can now proclaim with conﬁdence(but with some surprise too) that,in round numbers,our universe consists of5%baryons,25%dark matter, and70%dark energy.It is indeed embarrassing that95%of the universe is unaccounted for:even the dark matter is of quite uncertain nature,and the dark energy is a complete mystery.The network of key arguments is summarised in Figure1.Historically,the supernova evidence cameﬁrst.But had the order of events been diﬀerent,one could have predicted an acceleration on the basis of CDM evidence alone;the supernovae would then have oﬀered gratifying corroboration(despite the unease about possible poorly-understood evolutionary eﬀects).Our universe isﬂat,but with a strange mix of ingredients.Why should these all7give comparable contributions(within a modest factor)when they could have diﬀered by a hundred powers of ten?In the coming decade,we can expect advances on several fronts.Physicists may well develop clearer ideas on what determined the favouritism for matter over antimatter in the early universe,and on the particles that make up the dark matter.Understanding the dark energy,and indeed the big bang itself,is perhaps a remoter goal,but ten years from now theorists may well have replaced the boisterous variety of ideas on the ultra-early universe by aﬁrmer best buy. They will do this by discovering internal inconsistencies in some contending theories,and thereby narrowing down theﬁeld.Better still,maybe one theory will earn credibility by explaining things we can observe,so that we can apply it conﬁdently even to things we cannot directly observe.In consequence,we may have a better insight into the origin of theﬂuctuations,the dark energy,and perhaps the big bang itself.Inﬂation models have two generic expectations;that the universe should beﬂat and that theﬂuctuations should be gaussian and adiabatic(the latter because baryogenesis would occur at a later stage than inﬂation).But other features of theﬂuctuations are in principle measurable and would be a diagnostic of the speciﬁc physics.One,the ratio of the tensor and scalar amplitudes of theﬂuctuations,will have to await the next generation of CMB experiments, able to probe the polarization on small angular scales.Another discriminant among diﬀerent theories is the extent to which theﬂuctuations deviate from a Harrison-Zeldovich scale-independent format(n=1in the usual notation);they could follow a diﬀerent power law(i.e.be tilted),or have a‘rollover’so that the spectral slope is itself a function of scale.Such eﬀects are already being constrained by WMAP data,in combination with evidence on smaller scales from present-day clustering,from the statistics of the Lyman alpha absorption-line‘forest’in quasar spectra,and from indirect evidence on when theﬁrst minihalos collapsed,signalling the formation of theﬁrst Population III stars that ended the cosmic dark age.In parallel,there will be progress in‘environmental cosmology’.The new gen-eration of10-metre class ground based telescopes will give more data on the universe at earlier cosmic epochs,as well as better information on gravitational lensing by dark matter.And there will be progress by theorists too.The behaviour of the dark matter,if inﬂuenced solely by gravity,can already be simulated with suﬃcient accuracy.Gas dynamics,including shocks and radia-tive cooling,can be included too(though of course the resolution isn’t adequate to model turbulence,nor the viscosity in shear layers).Spectacular recent sim-ulations have been able to follow the formation of theﬁrst stars.But the later stages of galactic evolution,where feedback is important,cannot be modelled without parametrising such processes in a fashion guided by physical intuition and observations.Fortunately,we can expect rapid improvements,from obser-vations in all wavebands,in our knowledge of galaxies,and the high-redshift8universe.Via a combination of improved observations,and ever more reﬁned simulations, we can hope to elucidate how our elaborately structured cosmos emerged from a near-homogeneous early universe.ReferencesBlumenthal,G,Faber,S,Primack,J.R,and Rees,M.J.1984Nature311,517 Davis,M,Efstathiou,G.P,Frenk,C.S.and White,S.D.M.,1985Astrophys.J. 292,371Einasto,J,Kaasik,A and Saar,E,1974Nature250,309Kahn,F and Woltjer,L,1959Astrophys.J.130,705Meszaros,P.1974Astr.Astrophys.37,225Ostriker,J.Peebles,P.J.E.,and Yahil,A,1974Astrophys.J(Lett)193,L1 Pagels,H.and Primack,J.R.1982Phys.Rev.Lett.48,223Peebles,P.J.E.1982Astrophys.J.(Lett)263,L1Roberts,M.S.and Rots,A.H.1973Astr.Astrophys26,483.Rubin,V.C.,Thonnard,N.,and Ford,W.K.,1978Astrophys J.(Lett)225, L107White,S.D.M.,Navarro,J.F.,Evrard,A.E.and Frenk,C.S.1993,Nature366, 429Zwicky,F,1937Astrophys.J86,217910。

Dark Matter and Dark Energy

1. Introduction
Now is the time to be a cosmologist. We have obtained through remarkable technological advances and heroic and ingenious experimental eﬀorts a direct and extraordinarily detailed picture of the early Universe and maps of the distribution of matter on the largest scales in the Universe today. We have, moreover, an elegant and precisely quantitative physical model for the origin and evolution of the Universe. However, the model invokes new physics, beyond the standard model plus general relativity, not just once, but at least thrice: (1) Inﬂation, the physical mechanism for making the early Universe look precisely as it does, posits some new ultra-high-energy physics; we don’t know, however, what it is. (2) The growth of large-scale-structure and the dynamics of galaxies and galaxy clusters requires that we invoke the existence of collisionless particles or objects; we don’t know what this stuﬀ is. (3) The accelerated expansion of the Universe requires the introduction of a new term, of embarrassingly small value, in Einstein’s equation, a modiﬁcation of general relativity, and/or the introduction of some negative-pressure “dark energy,” again, the nature of which remains a mystery.

Dark Matter in Supergravity

models can have a much larger cross section, and current detectors can probe part of
the
parameter
space
where
tanβ
>
∼
4.
Minimum
cross
sec
greater
for models with universal soft breaking (mSUGRA) and models with nonuniversal soft
breaking. The analysis includes the necessary corrections to treat the large tanβ region
detectors with current sensitivity are seen to be probing the region where tanβ ∼>25,
Ωχ˜01 h2
<
0.1,
mχ˜01
<
∼
90
GeV,
and
for
the
light
Higgs,
mh
<
∼
120
GeV.
Nonuniversal
(i.e. L-R mixing in the squark and slepton mass matrices, loop corrections to the b and
τ masses,etc) and includes all coannihilation phenomena. For mSUGRA, dark matter

天然药物化学专业英语词汇总结

专业英语词汇总结Section 1生药部分中药研究现状及中药现代化一、加强中国药用植物基础研究及其与中药现代化的联系/Strengthening basic researches on Chinese Medicinal Plants and its relations to realizing the modernization of CMM记载be recorded来源derived from中医药Traditional Chinese Medicine,short for TCM卫生事业health care,health undertakings中草药Chinese traditional medicinal herbs疗效reliable therapeutical effectstherapeutic[,θer?'pju:t?k]adj.治疗(学)的;疗法的；对身心健康有益的副作用side-effectsl中医药的健康理念和临床医疗模式体现了现代医学的发展趋势。

The health concept and clinical practice reflect the trend of modern science新的科学技术潮流（the new tide of science and technology）二、中药资源及其研究成果/Chinese Medicinal Plant resources and achievement of its scientific research中药资源(medicinal plant resources)普查(surveys)专项研究(special projects)药用植物资源(the Chinese medicinal resources)科学鉴定(scientific identification)化学成分(chemical constituents)药理实验(pharmacological experiments临床适应症(clinical applications)研究(projects)新著作(new works)各论(monographs)手册(manuals)《中国药典》The pharmacopoeia of the people’s Republic of China药典Pharmacopoeia药用植物学Pharmaceutical Botany本草学Herbology中药学The Chinese Materia Medica药用植物分类学Pharmaceutical Plant Taxonomy植物化学Phytochemistry植物化学分类学Plant Chemotaxonomy药用植物志Flora of Medicinal Plant中药药剂学traditional Chinese Pharmaceutics中药炮制学Science of processing Chinese Crude Drugs中药鉴定学Identification of Traditional Chinese Medicine中药药理学Pharmacology of Traditional Chinese Medicines青蒿素artemisin奎宁quinine、氯奎宁chloroquine衍生物derivatives氯奎宁耐受性疟疾chloroquine resistant malaria急性疟疾pernicious malaria脑部疟疾cerebral malaria显著疗效marked effect chloroquine resistant malaria/抗氯喹啉疟疾Pernicious（有害的）malaria/急性疟疾cerebral malaria/脑疟疾derivatives/衍生物quinine/喹啉含有氮原子的化合物，在英文命名中多以-ine结尾Mono-/一Di-/二Tri-/三Tetra-/四Petan-/五Hexa-/六Hepta-/七Octa-/八Nona-/九Deca-/十三尖杉酯碱harringtonine、高三尖杉酯碱homoharringtonine白血病leukemia和恶性淋巴瘤malignant lymphoma银杏黄酮ginkgetin丹参酮tanshinon IIA治疗冠心病coronary heart diseasesNew drug developments/新药开发Health products/保健品质量控制Quality control修订revise常用中药common-used Chinese materia medica国家标准the national standards三、中药所面临的挑战/Chinese Medicinal Herbs Facing a Challenge中成药及其制剂traditional Chinese patent medicines and preparations基础研究basic researches生产production、流通marketing研究researchIdentification of species/品种鉴定鉴定和鉴别identifying and clarifying变种varieties伪品false matters。

Observations of Dark Matter in the Universe

Observations of Dark Matter in theUniverse在这个宇宙中，有些存在并不符合我们日常认识的物质，在我们的日常生活中我们无法观察到，但是它却占据了整个宇宙的大部分——那就是暗物质。

暗物质的存在还没有被科学家亲眼看到，但是从观测到的现象，我们有理由相信它的存在。

那么，什么是暗物质？按照目前的理解，暗物质是一种没有发射光线或者其他电磁辐射与物质相互作用的物质。

暗物质的存在是要解释各种天文疑难的源头。

例如，星系在这个悬浮的平衡状态上为何不会被碰撞和分裂？看似遥远无法观测到的星系之间相互影响的引力用力又从何而来？通过对星系和星系成员运动的观测，科学家发现星系内的物质相互作用是否定的，这就需要引入作用力为引力的暗物质。

暗物质的存在可以很好的解释这一系列现象，最起码能够说明引力作用的来源。

1998年，天文学家斯奈德和珀尔茨曼领导的斯隆数字巡天（SDSS）研究成果，发现暗物质占据了宇宙总质量的23%。

目前，暗物质的研究还远未终止，未来科学家还将会通过各种途径来探测它。

其中最常见的是通过引力透镜效应观测。

引力透镜效应是在天文学中常见的一项现象，是指光线穿过引力场时的位移效应。

当光线通过引力场时，光线会被弯曲，从而出现位置偏移、形变、色偏等现象。

暗物质会产生引力透镜效应，从光线的变化，可以分析星系内的暗物质分布。

这种方法是目前直接证实暗物质最可靠的方法之一，因此广受科学家们的重视。

那么，暗物质能为我们这个宇宙带来什么呢？暗物质是宇宙中最重要的基础物质之一，如果没有暗物质的存在，宇宙不会像现在这样地演化。

暗物质通过作用力对星系之间的排列产生影响，也对引力波的传播产生影响。

同时，暗物质的存在也助力了粒子物理的研究。

物理学家们对这样的一个想法进行了推导：是不是可以找到一种新的基本颗粒，它就是组成暗物质的基本粒子呢？暗物质的探测即将进入粒子物理的领域，并可能会诞生出更多的新知识。

总之，暗物质的存在对人类的意义是巨大的，暗物质的研究可以促进人类对宇宙和自身的了解，同时也会引领科技和经济的发展。

The Local Group

a rXiv:as tr o-ph/8249v116Aug2Microlensing 2000:A New Era of Microlensing Astrophysics ASP Conference Series,Vol.000,2000J.W.Menzies and P.D.Sackett,eds.The Local Group Eva K.Grebel 1,2,31University of Washington,Department of Astronomy,Box 351580,Seattle,WA 98195-1580,USA 2Hubble Fellow 3Max-Planck-Institut f¨u r Astronomie,K¨o nigstuhl 17,D-69117Heidelberg,Germany Abstract.Local Group galaxies such as the Milky Way,the Magellanic Clouds and M31are being used by a number of international collabora-tions to search for microlensing events.Type and number of detections place constraints on dark matter and the stellar populations within and along the line of sight to these galaxies.In this review I brieﬂy discuss the stellar populations,evolutionary histories,and other properties of dif-ferent types of Local Group galaxies as well as constraints on the dark matter content of these galaxies.Particular emphasis is placed on the dwarf companions of the spiral galaxies in the Local Group.1.Introduction The “Local Group”is the small group of galaxies around the Milky Way and M31.The size of the Local Group is not well known,and its galaxy census is incomplete for low-surface-brightness galaxies.Recent studies suggest that the radius of the zero-velocity surface of the Local Group is ∼1.2Mpc (Courteau &van den Bergh 1999)when a spherical potential is assumed.Within this radius 35galaxies have been detected (see Grebel 2000a for a list).Since in-formation about orbits is lacking it is unknown which ones of the more distant galaxies within and just outside of the adopted Local Group boundaries are ac-tually bound to the Local Group.Many faint Local Group galaxies were only discovered in recent years,and searches are continuing.Hierarchical cold dark matter (CDM)models predict about 10times more dark matter halos than the number of known Local Group satellites (e.g.,Klypin et al.1999).Compact high-velocity clouds (Braun &Burton 1999),which appear to be dark-matter-dominated with total estimated masses of a few 108M ⊙may be good candidates for the “missing”satellites.The Local Group comprises galaxies with a variety of diﬀerent morpholog-ical types,a range of masses,ages,and metallicities,and diﬀering degrees of isolation.Their proximity makes these galaxies ideal targets for detailed studies of their star formation histories from their resolved stellar populations and of galaxy evolution in general.Furthermore,Local Group galaxies provide a con-venient set of targets for studies of the nature of dark matter.Several Local1The Local Group3 companions are dwarf spheroidal and dwarf elliptical galaxies.The ensemble of dwarf irregular galaxies,on the other hand,shows little concentration toward the two large spirals(although the two most massive Local Group irregulars, the Large and the Small Magellanic Cloud(LMC and SMC),are close neighbors of the Milky Way and interact with it as well as with each other).This cor-relation between morphological type and distance from massive galaxies is also known as morphological segregation and may be to some extent a consequence of evolutionary eﬀects.Whether a galaxy should be considered a dwarf galaxy is somewhat arbi-trary,and diﬀerent authors use diﬀerent criteria.For the purpose of this review all galaxies with M V>−18mag will be considered dwarf galaxies,which results in31dwarfs,excluding only the three spirals and the LMC.We distinguish the following basic types of dwarf galaxies in the Local Group:•Dwarf irregulars(dIrrs)with M V∼>−18mag,µV∼<23mag arcsec−2,R∼<5kpc,M H i∼<109M⊙,and M tot∼<1010M⊙.DIrrs are irregular in their optical appearance,gas-rich,and show current or recent star formation.Several of the dIrrs contain globular or open clusters.•Dwarf ellipticals(dEs)with M V∼>−17mag,µV∼<21mag arcsec−2,R∼<4kpc,M H i∼<108M⊙,and M tot∼<109M⊙.DEs look globular-cluster-like in their visual appearance with a pronounced central concentration.All dEs are companions of M31.Two of the four dEs(M32,NGC205) are nucleated.M32,a dE very close to M31,has a central black hole and follows the same scaling relations as large elliptical galaxies,whereas the other dEs resemble dSphs and are therefore called spheroidals by van den Bergh(1999,2000).All dEs except for M32contain globular clusters.•Dwarf spheroidals(dSphs)with M V∼>−14mag,µV∼>22mag arcsec−2, R∼<3kpc,M H i∼<105M⊙,and M tot∼107M⊙.These galaxies show very little central concentration and are dominated by old and intermediate-age stellar populations.Only three(Sgr,For,And I)contain globular clusters.With the exception of two isolated dSphs(Tuc and Cet)all known dSphs are close neighbors of M31or the Milky Way.DSphs are gas-poor systems.Sensitive searches for H i in dSphs yielded only low upper limits,but recent studies detected extended H i clouds in the surroundings of some dSphs that may be associated with them judging from the similarity of their radial velocities(Carignan et al.1998,Blitz&Robishaw2000).A few dwarf galaxies(Phe,LGS3)are classiﬁed as“transition-type”objects and may be evolving from low-mass dIrrs to dSphs.These dIrr/dSph galaxies are found at distances of250kpc<D Spiral<450kpc.The Local Group does not contain blue compact dwarf galaxies,dwarf spirals,or massive ellipticals.3.The Local Group spiralsThe Local Group spirals have the most complex and varied star formation histo-ries of all Local Group galaxies.Diﬀerent subpopulations can be distinguished by their ages,metallicities,and kinematics.The oldest populations are found in4Grebelthe halos and thick disk components.Extremely metal-poor([Fe/H]<−3dex) halo stars are tracers of the earliest star formation events(Ryan et al.1996), but it is diﬃcult to derive ages for them.The earliest signiﬁcant star formation episodes in the Galactic thick disk appear to have occurred13Gyr ago,while the thin disk began to experience multiple bursts of star formation∼9Gyr ago(Rocha-Pinto et al.2000).The metallicity in the thin disk depends more strongly on Galactocentric radius than on age and shows a large spread at any position and age(Edvardsson et al.1993).While halos may have largely formed through accretion of metal-poor Searle &Zinn(1978)fragments,bulges also host metal-rich old populations(mean metallicity of the Galactic bulge:−0.25dex;Minniti et al.1995),indicating that they experienced early and fast enrichment.M31appears to have undergone rapid enrichment as a whole,whereas M33shows a pronounced radial abundance gradient.The mean metallicity of M31’s halo is−1to−1.2dex,more metal-rich than the halo of the Milky Way(∼−1.4dex)and of M33(∼−1.6dex).While M31’s bulge emits∼30%of the visible light of this galaxy,M33lacks a bulge.M31’s total number of globular clusters may be as high as∼600.The Milky Way contains∼160globulars,and in the smaller M3354globulars are currently known(see Grebel2000b for a review of star clusters in the Local Group). Main-sequence photometry of Galactic globular clusters suggests a range of ages spanning more than3Gyr.We lack such detailed information for M31’s and M33’s globulars,but the blue horizontal branch(HB)morphology observed in some of them may suggest similar ages as for the Milky Way globulars.On the other hand,the red HBs of M33’s globulars may indicate that star formation was delayed by a few Gyr(Sarajedini et al.1998).The spiral arms in all three galaxies contain numerous OB associations and young star clusters.The UV line strengths of massive OB stars suggest that the young population of M31is comparable to that of the Milky Way,whereas M33 resembles the Large Magellanic Clouds(Bianchi,Hutchings,&Massey1996). Present-day star-forming regions in the Milky Way range from very extended associations to compact starburst clusters such as the central cluster of NGC 3603and the clusters Quintuplet and Arches near the Galactic center.M31’s current star-forming activity is low.The increase in cluster formation in M33 over the past10–100Myr may be correlated with gas inﬂow into M33’s center (Chandar,Bianchi,&Ford1999).Warps in the stellar and H i disks of the Milky Way and M31may have been caused by tidal interactions with the Magellanic Clouds and M32,respectively. The Milky Way disk may also have been signiﬁcantly distorted by interacting with the currently merging Sagittarius dwarf galaxy(Ibata&Razoumov1998). M33’s stellar and H i disks are tilted with respect to each other,but no nearby companion is known that might be responsible.4.Star formation histories of Local Group dwarf galaxiesThe star formation histories of dwarf galaxies in the Local Group vary widely. No two galaxies are alike;not even within the same morphological type.The reasons for this diversity are not understood.It seems that both galaxy mass and environment play important roles in the evolution of these low-mass objects.The Local Group54.1.Methods and limitationsStar formation histories of resolved dwarf galaxies are commonly derived through photometric techniques.The most widely used method consists of sophisticated modelling of the observed color-magnitude diagrams(CMDs)through synthetic CMDs taking into account photometric errors,seeing,and crowding eﬀects.For a recent review of procedures and techniques see Aparicio(1999).The methods are limited by the quality of the observations and by how closely theoretical evo-lutionary models reproduce observational features.For instance,Olsen(1999) notes that old red giant branches of evolutionary models mayﬁt the observa-tions poorly,which can lead to an underestimation of the contribution of the old population.Free parameters in modelling include the adopted initial mass function slope and the binary fraction.Additional constraints can be imposed by using special types of stars as tracers of certain evolutionary phases.For instance,the presence of HB stars and RR Lyrae variables is a reliable indicator of an old population even when suﬃciently deep main-sequence photometry is lacking.It is important to keep in mind that the age resolution that can be obtained is not linear and decreases strongly for older populations.Whereas young populations with short-lived, luminous massive stars can be accurately age-dated to within a few million years,the accuracy for the oldest,long-lived evolutionary phases is of the order of a few billion years.Relative ages of resolved old populations with high-quality, deep main-sequence photometry,on the other hand,can be established with a resolution of a Gyr or less through direct comparison with CMDs of Galactic globular clusters.In the following,“young”refers to populations with ages<1 Gyr,“intermediate-age”denotes the age range from1Gyr to10Gyr,and“old”stands for ages>10Gyr.Owing to the availability of10-m class telescopes,spectroscopic measure-ments of stellar abundances are now feasible for individual supergiants and the brightest red giants in galaxies as distant as the M31subgroup.Together with emission-line spectroscopy of H ii regions,these data help to constrain the metal-licity and metallicity spread in certain evolutionary phases.Still,accurate metal-licity information as a function of time is lacking for almost all galaxies.The increasing amount of data on internal kinematics and dwarf galaxy proper motions are beginning to constrain their dynamical history.Unfortu-nately accurate orbital data are not yet available for almost all of the Local Group galaxies,making it diﬃcult to evaluate the suggested impact of environ-mental eﬀects and interactions discussed later.4.2.Old populationsA common property of all Local Group dwarfs studied in detail is the existence of an old population,whose presence can be inferred either from HB stars and/or from photometry reaching below the oldest main-sequence turnoﬀ.Old popula-tions may be diﬃcult to detect in the central portions of galaxies with signiﬁcant intermediate-age or young populations,as the location of these stars in a CMD may obscure an old HB.Also,coverage of only a smallﬁeld of view may be insuﬃcient to reliably detect a sparsely populated HB(compare theﬁndings of Gallart et al.1999and Held et al.2000for Leo I).Age dating of the oldest populations is reliably possible only where high-quality photometry well below6Grebelthe oldest main-sequence turnoﬀexists;a challenge for present-day telescopes already for galaxies at the distance of M31.Deﬁnite statements about the ex-istence of an old population are possible only where the photometry reaches at least the HB;feasible in principle with present-day telescopes out to distances ≈3Mpc.Deep main-sequence photometry based largely on Hubble Space Telescope data revealed that the ages of the oldest populations in the LMC(Holtzman et al.1999),Sagittarius(Layden&Sarajedini2000),Draco,Ursa Minor(Feltzing, Gilmore,&Wyse1999),Sculptor(Monkiewicz et al.1999),Carina(Mighell 1997),Fornax(Buonanno et al.1998),and Leo II(Mighell&Rich1996)are as old as the oldest Galactic globular clusters and bulge populations.Thus all of these galaxies share a common epoch of early star formation.Similarly old ages were inferred from the existence of blue HBs in Sextans(Harbeck et al.2000), Leo I(Held et al.2000),Phoenix(Smith,Holtzman,&Grillmair2000),IC1613 (Cole et al.1999),Cetus(Tolstoy et al.2000),And I(Da Costa et al.1996), And II(Da Costa et al.2000),NGC185(Geisler et al.1999),NGC147(Han et al.1997),Tucana(Lavery et al.1996),M31(Ajhar et al.1996),potentially in M32(Brown et al.2000),and spectroscopically for one of NGC6822’s globular clusters(Cohen&Blakeslee1998).Assuming that age is the second parameter determining HB morphology the apparent lack of a blue HB in M33globular clusters(Sarajedini et al.1998)and in theﬁeld populations of WLM(Dolphin 2000),Leo A(Tolstoy et al.1998),DDO210(Tolstoy et al.2000)and the Small Magellanic Cloud(SMC)may be interpreted as evidence for delayed formation of the majority of the old population in these galaxies.Furthermore,the oldest globular cluster in the SMC,NGC121,is a few Gyr younger than the oldest Galactic globulars(Shara et al.1998)A complete lack of an old population has so far not been established in any Local Group galaxy.4.3.Spatial variations of stellar populationsNot surprisingly properties such as gas and stellar content,age structure,metal-licity distribution,density,and scale height vary as a function of position within a galaxy.Spatial variations in the distribution of stellar populations of diﬀerent ages are found in all types of galaxies,underlining the importance of large-area coverage when trying to determine the star formation history of a galaxy.The oldest populations turn out to be spatially most extended.Spiral galax-ies in the Local Group show pronounced population diﬀerences between disk, halo,and more intricate spatially and kinematically distinct subdivisions.In massive irregulars such as the LMC spatial variations are traced by,e.g.,mul-tiple distinct regions of concurrent star formation.These regions can remain active for several100Myr,are found throughout the main body of these galax-ies,and can migrate.In low-mass dIrrs and several dSphs the most recent star formation events are usually centrally concentrated.A radial age gradient may be accompanied by a radial metallicity gradient,indicating that not only gas but also metals were retained over an extended period of time.Occasionally evidence for shell-like propagation of star formation from the central to adjacent regions is found. DSphs that are predominantly old tend to exhibit radial gradients in their HB morphology such that the ratio of red to blue HB stars decreases towards theThe Local Group7outer parts of the dwarfs.If such second-parameter variations are caused by age then this would indicate star formation persisted over a longer period of time in the centers of these ancient galaxies.4.4.Diﬀerences in gas contentThe H i in dIrrs is generally more extended than the oldest stellar populations and shows a clumpy distribution.Gas and stars in a number of low-mass dIrrs exhibit distinct spatial distributions and diﬀerent kinematic properties.Shell-like structures,central H i holes,or oﬀ-centered gas may be driven by recent star formation episodes(Young&Lo1996;1997a,b).H i shells,however,do not always expand,which may argue against their formation through propagating star formation(Points et al.1999,de Blok&Walter2000).Ongoing gas accretion appears to be feeding the starburst in the dIrr IC10 (Wilcots&Miller1998).An infalling or interacting H i complex is observed in the dIrr NGC6822(de Blok&Walter2000).DEs in the Local Group contain low amounts of gas(a few105M⊙;Sage, Welch,&Mitchell1998)or none(NGC147).The apparent lack of gas in dSphs (e.g.,Young2000)continues to be hard to understand,in particular when con-sidering that some dSphs show evidence for recent(Fornax:∼200Myr,Grebel &Stetson1999)or pronounced intermediate-age star formation episodes(e.g., Carina:3Gyr;Hurley-Keller,Mateo,&Nemec1998;Leo I:2Gyr;Gallart et al.1999).Gas concentrated in two extended lobes along the direction of motion of the Sculptor was detected beyond the tidal radius of this galaxy(Carignan et al.1998).This gas may be moving inwards or away from Sculptor.Its amount is consistent with the expected mass loss from red giants,though that does not explain its location along the probable orbital direction of Sculptor.Blitz &Robishaw(2000)suggested the existence of similar gas concentrations with matching radial velocities in the surroundings of several other dSphs.Simu-lations by Mac Low&Ferrara(1999)suggest that total gas loss through star formation events can only occur in galaxies with masses of less than a few10−6 M⊙.Blitz&Robishaw discuss tidal eﬀects as the most likely agent for the dis-placement of the gas.However,the absence of gas in Cetus and Tucana,two isolated dSphs in the Local Group,requires a diﬀerent mechanism.4.5.Star formation historiesLocal Group dwarf galaxies vary widely in their star formation histories,chemi-cal enrichment,and age distribution;even within the same morphological type. Despite their individual diﬀerences,however,they tend to follow common global relations between,e.g.,mean metallicity,absolute magnitude,and central sur-face brightness.Galaxy mass as well as external eﬀects such as tides appear to play major roles in their evolution.Suﬃciently massive irregulars and dIrrs exhibit continuous star formation at a variable rate.They can continue to form stars over a Hubble time and undergo gradual enrichment.Galaxies such as the LMC(Holtzman et al.1999, Olsen1999),SMC,and WLM(Dolphin2000)have formed stars continuously and experienced considerable chemical enrichment spanning more than1dex in[Fe/H].Their star formation rate,on the other hand,varied and shows long8Grebelperiods of low activity.Interestingly,in the LMC cluster andﬁeld star formation activity show little correlation.Low-mass dIrrs and dSphs often show continuous star formation rates with decreasing star formation rates.They typically show dominant old(or intermediate-age)populations with little or no recent activity.A similar evolution appearsto have occurred in dEs.DSph companions of the Milky Way tend to have in-creased fractions of intermediate-age populations with increasing Galactocentric distance,indicating that external eﬀects such as tidal or ram pressure stripping may have aﬀected their star formation history(e.g.,van den Bergh1994).The two closest dSphs to the Milky Way(other than the currently merging Sagit-tarius dSph)are Draco and Ursa Minor,which are dominated by ancient popu-lations and are also the least massive dSphs known–possibly due to the earlyinﬂuence of Galactic tides,though present-day positions may not reﬂect early Galactocentric distances,and reliable orbital information is lacking.The Local Group dwarf galaxy to show the most extreme case of episodic star formation with Gyr-long periods of quiescence and distinct,well-deﬁned subgiant branches is Carina(Smecker-Hane et al.1994,Hurley-Keller et al. 1998).It is unclear what caused the interruption and subsequent onset of star formation after the long gaps.Also,the apparent lack of chemical enrichment during these star formation episodes is surprising.4.6.Potential evolutionary transitionsFornax is the second most luminous dSph galaxy in the Local Group.The young age of its youngest measurable population(∼200Myr,Grebel&Stetson1999)is astonishing considering its lack of gas.Just a few hundred Myr ago Fornax would have been classiﬁed as a dIrr.What caused Fornax to lose all of its gas after some13Gyr of continuous,decreasing star formation is not clear.The presence of intermediate-age populations in some of the more distant Galactic dSphs,the possible detection of associated gas in the surroundings of several of them,indications of substantial mass loss discussed elsewhere in this paper,morphological segregation,common trends in relations between their inte-grated properties,and the apparent correlation between star formation histories and Galactocentric distance all seem to support the idea that low-mass dIrrs will eventually evolve into dSphs if their environment fosters this evolution.DSphs may be the naturalﬁnal phase of low-mass dIrrs,and the type distinction may be artiﬁcial.The six dSph companions of M31span a similar range in distances as the Milky Way dSphs(Grebel&Guhathakurta1999).A study of whether their detailed star formation histories(not yet available)show a comparable cor-relation with distance from M31would provide a valuable test of the suggested impact of environment.The mass(traced by the luminosity)of a dwarf galaxy plays a major role in its evolution as indicated by the good correlation between luminosity and mean metallicity(e.g.,Caldwell1999).The observed lack of rotation in dSphs requires that its hypothesized low-mass dIrr progenitor must have gotten rid of its angular momentum,which may occur through substantial mass loss.However,this scenario does not account for the existence of isolated dSphs such as Tucana. Alternatively,the progenitor may have had very little rotation to begin with. Either way,the subsequent fading must have been low since otherwise dIrrsThe Local Group9 and dSphs would not follow such a fairly well-deﬁned common relation.Several authors(e.g.,Mateo1998)suggested that the luminosity-metallicity relation is instead bimodal with separate loci for dIrrs and dSphs in the sense that at a given luminosity a dIrr tends to be more metal-poor than a dSph,excluding evolutionary transitions.Hunter,Hunsberger,&Roye(2000)go a step further and suggest that a number of Local Group dIrrs might have formed as ancient tidal dwarfs that lack dark matter,are essentially non-rotating,and contribute to the increased scatter in the absolute magnitude–mean metallicity relationship for M B<−15mag.5.Dark matterDark matter is a signiﬁcant component of many Local Group galaxies.Spiral galaxies exhibit H i rotation curves that become approximatelyﬂat at large radii and that extend2–3times beyond the optically visible galaxy.Global mass-to-light ratios(M/L)inferred from rotation curves of spirals are typically≤10 M⊙/L⊙for the visible regions(∼1−3M⊙/L⊙in disks,∼10−20M⊙/L⊙in bulges),while the dark matter in halos seems to signiﬁcantly exceed these values(Longair1998).This motivates eﬀorts to determine the nature of the dark matter through microlensing in the Galactic halo and toward the Galactic bulge as detailed elsewhere in this volume,and through pixel microlensing of stars in the disk of M31by dark massive objects in M31’s halo(Crotts1992).In gas-rich dwarfs the presence of dark matter is inferred as well from H i rotation curves.Some of the less massive dIrrs are rotationally supported only in their centers,while the majority of dSphs studied so far does not show evidence for rotation at all.Chaotic gas motions dominate in low-mass dIrrs,and the H i column density distribution is poorly correlated with the stellar distribution (Lo,Sargent,&Young1993).In the dE NGC205,which is tidally interacting with M31,integrated light measurements revealed that the stellar component is essentially non-rotating though the H i shows signiﬁcant angular momentum (Welch,Sage,&Mitchell1998).In gas-deﬁcient dSphs kinematic information is based entirely on stars.Most dSphs show no rotation.Their velocity dispersions are typically≥7km s−1.Assuming virial equilibrium velocity dispersions and rotation curves can be translated into virial masses.The derived total M/L ratios of Local Group dwarf galaxies present an inhomogeneous picture ranging from∼1to∼80(see compilation by Mateo1998).Compact high-velocity clouds(CHVCs)are a subset of high-velocity H i clouds with angular sizes of only about1degree on the sky.They show infall motion with respect to the barycenter of the Local Group.Preliminary estimates place them at distances of0.5to1Mpc in contrast to the extended nearby high-velocity-cloud complexes(Braun&Burton1999).Their rotation curves imply high dark-to-H i ratios of10–50if distances of0.7Mpc are assumed,and masses of107M⊙(Braun&Burton2000).CHVCs may be a signiﬁcant source of dark matter and may represent pure H i/dark-matter halos prior to star formation. We are currently carrying out an optical wide-ﬁeld survey to establish whether they also contain a low-luminosity,low-density stellar component,which would imply the discovery of a new,very dark type of galaxy,help to reﬁne CHVC distances and allow detailed studies of their stellar populations.10Grebel5.1.Dwarf spheroidal galaxies and dark matterGalactic dSphs are of particular interest in eﬀorts to elucidate the nature of dark matter since they may be dark-matter-dominated and can be studied in great detail due to their proximity.From an analysis of the kinematic properties of Draco and Ursa Minor Gerhard&Spergel(1992a)exclude fermionic light particles(neutrinos)as dark matter suspects because phase-space limits would then require unreasonably large core radii and masses for these two galaxies.The initial measurements of velocity dispersions in dSphs were criticized for including luminous AGB stars and Carbon stars,whose radial velocities may reﬂect atmospheric motions,and for neglecting the impact of binaries(see Ol-szewski1998for details).Subsequent studies concentrated on somewhat fainter stars along the upper RGB,carried out extensive simulations to assess the im-pact of binaries(Hargreaves,Gilmore,&Annan1996;Olszewski,Pryor,&Ar-mandroﬀ1996),obtained multi-epoch observations(e.g.,Olszewski,Aaronson, &Hill1995),and increased the number of red giants with measured radial ve-locities to more than90in some cases(Armandroﬀ,Olszewski,&Pryor1995). These studies established that the large velocity dispersions in dSphs are not due to the previously mentioned observational biases.Kleyna et al.(1999)show that the currently available measurements for the two best-studied dSphs,Draco and Ursa Minor,are not yet suﬃcient to distinguish between models where mass follows light(constant M/L throughout the dSph)or extended dark halo models when interpreting the velocity dispersions as high M/L ratios due to large dark matter content.Mateo(1998)and Mateo et al.(1998)argue that the relation between total M/L and V-band luminosity for dSphs can be approximated well when adopting a stellar M/L of1.5(similar to globular clusters)and an extended dark halo with a mass of2·107M⊙,suggesting fairly uniform properties for the dark halos of dSphs.Luminosity functions(LFs)of old stellar systems can provide further con-straints on the nature of dark matter.The main-sequence LFs of oldﬁeld popu-lations in the Galactic bulge(Holtzman et al.1998),LMC and SMC(Holtzman et al.1999),Draco(Grillmair et al.1998),and Ursa Minor(Feltzing et al.1999) are in excellent agreement with the solar neighborhood IMF and LFs of glob-ular clusters that did not suﬀer mass segregation.Since globular clusters are not known to contain dark matter,one would expect toﬁnd diﬀerences in the LF of dark-matter-rich populations if low-mass objects down to0.45M⊙were important contributors to the baryonic dark matter content.Furthermore,these studies demonstrate that the LF in objects with a wide range of M/L ratios does not diﬀer much.The possible contribution of white dwarfs(or lack thereof)is discussed elsewhere in these proceedings.5.2.Tidal eﬀects rather than dark matter?Instead of a smooth surface density proﬁle that one might expect from a relaxed population,Ursa Minor shows statistically signiﬁcant stellar density variations (Kleyna et al.1998).Fornax’s four ancient globular clusters are located at dis-tances larger than the galaxy’s core radius.Dynamical friction should have lead to orbital decay in only a few Gyr(much less time than the globular clusters’lifetimes)and have turned Fornax into a nucleated dSph.Simulations by Oh, Lin,&Richer(2000)suggest that the best mechanism to have prevented this。

2019-Cosmological perturbations from a vector field宇宙学扰动向量场-文档资料

standard model, which can play the role of the vector curvaton
Physical Review D 74 (2019) 083502 : hep-ph/0607229
arXiv:0806.4680 [hep-ph]
Physical Review D 76 (2019) 063506 : 0705.3334 [hep-ph]
Konstantinos Dimopoulos
Lancaster University
Scalar vs Vector Fields
Scalar fields employed to address many open issues: inflationary paradigm, dark energy (quintessence) baryogenesis (Affleck-Dine)
Homogeneous Vector Field = in general anisotropic
Basic Problem: the generatation of a large-scale anisotropy is in conflict with CMB observations
However, An oscillating massive vector field can avoid excessive large-scale anisotropy
Polarization vectors:
Canonical quantization:
Particle Production of Vector Fields
Solve with vacuum boundary conditions:

DarkMaterials暗物质

DarkMaterials暗物质“For the longest time, we thought that atoms were all there was to the universe—atoms of regular matter,” astronomer Andrew Fraknoi, of Foothill College, told Current Science. “But in fact, it’s now appearing that that’s not the whole story—that there is a great deal of ‘something else.’And that ‘something else’is one of the great unsolved5 mysteries of the universe.”Just 4 percent of the universe is ordinary matter, according to the most recent calculations. Twenty-three percent is a mysterious, invisible form of matter called dark matter. And a whopping6 73 percent is something else so poorly understood that scientists simply call it dark energy.“You can imagine how frustrating7 it is for astronomers, whose job it is to know what’s in the universe, to have to get up in the morning, look in the mirror, and say, ‘I don’t know what most of the universe is made of,’” says Fraknoi.Spin8 Rate?If dark matter can’t be seen, how does anyone know it’s there? The tip-off9 came decades ago when astronomers noticed something very odd about the motion of the galaxies10. They spin way11 too fast—impossibly fast.Galaxies are collections of millions or even billions of stars held together by gravity as they rotate12. Gravity is an attractive force that pulls together all things made of matter. The more matter there is, the stronger the force of gravity. When astronomers took careful stock of13 all the matter in the galaxies, they found that there wasn’t enough of it to produce the gravity necessary to keep the spinning galaxies from flying apart.That finding is also true of our own galaxy, the Milky Way. “When we add up all the stuff we can see in the Milky Way14, there just isn’t enough gravity in all the visible material of the Milky Way to hold this fast-moving stuff together,” explains Fraknoi. “So we conclude from this that there must be more gravity than meets the eye.”Astronomers think that the extra gravity holding galaxies together comes from matter that can’t be seen or detected—dark matter. To prove the existence of dark matter, however, scientists have to find it. And finding it is tricky15 because no one knows what to look for.Some think dark matter might be ordinary matter trapped in hard-to-see places—perhaps in black holes or brown dwarfs. Others think it might be an exotic kind of matter that surrounds us without our even noticing it and passes through ordinary matter undetected.Although dark matter remains elusive, there’s still good reason to believe it exists. Its gravity is strong enough to bend light, a phenomenon called gravitational lensing. Using powerful telescopes16, astronomers can see the telltale distortion caused by dark matter bending light that passes through or near it.Universe ExpandingNot long ago, astronomers noticed something else strange about the universe. It is not only expanding—the rate of its expansion is actually speeding up.The expansion of the universe can be explained by the big bang, the idea that 13.7 billion years ago, the universe e xploded outward from a single point. “Space is stretching,” Fraknoi says, “like the skin of a balloon stretches when you blow it up.”The universe’s expansion should be slowing down because of gravity. Instead, it’s speeding up—an occurrence so bizarre17 it’s as if you tossed a ball in the air and instead of coming back down, it flew faster and faster upward.“If the universe is speeding up,” says Fraknoi, “there has to be another form of energy, something very powerful that is speeding up the universe.” Astronomers have named that other form of energy dark energy. Except for the fact that it seems to be a kind of antigravity force that pushes matter apart, no one has any idea what it might be.Figuring out what dark energy is, how much there is, and how it affects the universe is no small matter. The answer could also settle an ongoing18 debate about the ultimate19 fate of the universe. Will it keep expanding forever—a trend known as the big rip20? Or will it eventually slow down, reverse course, and collapse—the big crunch21?Fraknoi finds the puzzles of dark matter and dark energy tremendously exciting. “In astronomy, it’s pretty clear that there are far more things that we don’t know than we do know,” he says. “But if everything was answered, who’d become a scientist?”在自然科学课上，你们对原子差不多有了全面的了解。

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∗E-mail: siddh@ﬁs.cinvestav.mx †E-mail: tmatos@ﬁs.cinve consistent with the predictions of Newtonian theory, which explains well the dynamics of the luminous sector of the galaxy but predicts a keplerian falling oﬀ for the rotation curve. The region of the galaxy we are interested in is that in which the dark matter determines the kinematics of test particles. So we can suppose that luminous matter does not contribute in a very important way to the total energy density of the matter that determines the bahavior of particles in the mentioned region, instead the scalar matter will be the main contributor to it. Thus, as a ﬁrst approximation we can neglect the baryonic matter contribution to the total energy density for the explanation of assimptotic rotation curves.
PACS numbers: 95.30.S, 04.50, 95.35
One of the greatest puzzles of physics at the moment is without doubt the existence of dark matter in cosmos. The experimental fact that the galaxy masses measured with dynamical methods do not coincide with their luminous galaxy masses gives rise to the existence of a great amount of dark matter in galaxies, galaxy clusters and superclusters. At the present time, cosmological observations indicate that the universe is ﬁlled out with about 90 percent of dark matter, whose nature till now remains unexplained. Recently some authors have proposed the scalar ﬁeld as a candidate for dark matter in cosmos [1,2], in some sense the inﬂationary cosmological model proposes the scalar ﬁeld as cosmological dark matter as well. These models consider scalar-tensor theories of gravity where one is able to add mass terms to the total energy density of the space-time. All modern unifying ﬁeld theories also contain scalar ﬁelds. For example, scalar ﬁelds are fundamental ﬁelds in KaluzaKlein and Superstring theories, because such ﬁelds appear in a natural way after dimensional reduction. In both theories the scalar ﬁeld could be endowed with an exponential scalar potential [3,4], in particular, when we deal with 5-dimensional Kaluza-Klein theories, the Lagrangian density reads L5 = R5 + Λ being Λ a 5dimensional cosmological constant. After dimensional reduction and a conformal transforma√tion one obtains the density L4 = −R4 + 2(∇φ)2 + e−2/ 3φΛ, where φ is the scalar ﬁeld which actually states that an exponential potential appears in a natural way in this theory. An analogous procedure stablishes that in the low energy limit of Superstring theory one gets a similar result [1,3]. In general one obtains the Lagrangian from highdimensional theories L4 = −R4 + 2(∇Φ)2 + e−2αΦΛ, therefore here we will restrict our selves to an exponential scalar potential. In this letter we show a possible
arXiv:gr-qc/9810028v4 7 Nov 1999
Scalar Fields as Dark Matter in Spiral Galaxies
F. Siddhartha Guzma´n∗ and Tonatiuh Matos† Departamento de F´ısica,
Centro de Investigaci´on y de Estudios Avanzados del IPN, AP 14-740, 07000 M´exico D.F., MEXICO. (February 7, 2008)
duces a dark matter distribution going as ∼ 1/r2, im-
plying in this way an increasing mass M (r) ∼ r. Then,
by assuming that a galaxy is a system in equilibrium
We present a model for the dark matter in spiral galaxies, which is a result of a static and axial symmetric exact solution of the Einstein-Dilaton theory. We suposse that dark matter is a scalar ﬁeld endowed with a scalar potential. We obtain that a) the eﬀective energy density goes like 1/(r2 + rc2) and b) the resulting circular velocity proﬁle of tests particles is in good agreement with the observed one.
A convincing phenomenological model for galactic dark
matter is the called Isothermal Halo Model (IHM), which
assumes the dark matter to be a self-gravitating ball of
model for the dark matter in spiral galaxies, supposing that such matter is of scalar nature.
There is a common approach to explain the rotation curves in spiral galaxies called Modiﬁed Newtonian Dynamics (MOND) [5,6], which basically consists of modifying the Newton’s law of attraction for small accelerations by adding terms to the gravitational potential. In this way, by adjusting some free parameters for each galaxy, one can reproduce the asymptotic behavior of the rotation curves. However it appears to be artiﬁcial because it is nothing but a mere correction of Newton’s law, we are unable to know neither where the parameters and the correction terms come from, nor why nature behaves like that and therefore which is the Newton’s law at cosmological scale for instance.