1、主流物理界對暗物質(zhì)研究的現(xiàn)狀 李小堅 龔天任本文簡要介紹主流物理界對暗物質(zhì)研究和理解的現(xiàn)狀。一、 引言最近關(guān)于“悟空”（DAMPE）衛(wèi)星數(shù)據(jù)的好消息，給中國科學(xué)界帶來了一次狂歡。媒體紛紛報道，其中有兩點共識：第一，暗物質(zhì)的存在是毫無疑問的，暗物質(zhì)與可見物質(zhì)的比率大約在5比1之間。第二，迄今為止沒有人知道這個問題的答案：暗物質(zhì)是什么？是的，以上這兩點基本上是正確的。暗物質(zhì)是什么？在主流物理學(xué)界沒有人知道答案！中國科學(xué)院院長白春禮，談暗物質(zhì)的視頻介紹：白春禮院士介紹，這是令世界物理主流困惑不解，更是令全世界普通民眾迷惑的大問題！最終，全球科學(xué)界將通過科學(xué)的方法一一排除那些疑似暗物質(zhì)的候選者，確定暗

2、物質(zhì)不是什么。的確，主流科學(xué)在暗物質(zhì)不是什么已經(jīng)取得許多成果。但關(guān)鍵問題是暗物質(zhì)是什么？，這個問題必須要有理論突破！因此，我們可以從網(wǎng)上看到全球科學(xué)界正在努力，試圖揭開這個謎底。暗物質(zhì)不是什么 與暗物質(zhì)是什么？成為全球人類的熱點問題！那么，我們現(xiàn)在來看一看，國際主流物理界關(guān)于暗物質(zhì)問題的探索情況。二、主流物理界對暗物質(zhì)的認識1.已知的暗物質(zhì)國際主流界公認的已知的暗物質(zhì)有兩種：1）中微子，2）黑洞。然而，這兩種已知的暗物質(zhì)不能解釋全部整個暗物質(zhì)。也就是說，還有其他的物質(zhì)也扮演著暗物質(zhì)的角色。事實上，在許多天體物理調(diào)查中，這兩個已知的暗物質(zhì)只占總暗物質(zhì)的很小的百分比(小于1%），見：“2017的暗

3、能量調(diào)查”結(jié)果。2. 我們先說黑洞去年，以及今年LIGO多次發(fā)現(xiàn)雙黑洞的合并凝聚，顯示出宇宙中的黑洞密度很高，從而，似乎“黑洞暗物質(zhì)假說”又死灰復(fù)燃。宇宙中有兩種方式產(chǎn)生黑洞。第一種，黑洞就是一顆恒星的殘余。這個恒星演變過程我們現(xiàn)在非常清楚地知道了解。我們還可以計算出每個星系中的黑洞數(shù)量。對于銀河系，它有大約300萬個黑洞，每個黑洞的平均質(zhì)量為10個太陽質(zhì)量。這300萬個黑洞中的暗物質(zhì)約占銀河系總質(zhì)量的0.001%。顯然，這一種黑洞不能成為整個宇宙暗物質(zhì)的候選者。第二種，可能有在大爆炸期間產(chǎn)生的一些原始黑洞。它們攜帶的質(zhì)量，大約可以從0.1到10億個太陽質(zhì)量不等。此外，我們不知道這些黑洞的密度

4、。也就是說，它很有可能代表整個宇宙的暗物質(zhì)。然而，通過分析LIGO的數(shù)據(jù)，給出了否定的回答：沒有！原始黑洞無法解釋宇宙全部的暗物質(zhì)。也就是說，一定還有其他東西扮演暗物質(zhì)的角色。參見：LIGO不硬氣：原始黑洞、暗物質(zhì)和Ia型超新星的引力透鏡效應(yīng)。（/abs/1712.02240）。3其他暗物質(zhì)候選者，包括中微子在主流物理學(xué)，基本上還有這兩類暗物質(zhì)候選者：1）不基于粒子的任何暗物質(zhì)，如修改引力定律（MOND）。2）以粒子為基礎(chǔ)的暗物質(zhì)候選者：一些未知的粒子，如弱互相質(zhì)量粒子WIMP（例如，無菌中微子、軸子、暗光子等）；2017年10月16日宣布的LIGO雙中子星合并

5、，它幾乎完全排除了MOND存在的證據(jù)。參見 gw170817暗物質(zhì)仿真器（/abs/1710.06168）。此外，我國發(fā)射的 “悟空”（DAMPE）的數(shù)據(jù)，還沒有發(fā)現(xiàn)任何MOND關(guān)聯(lián)的證據(jù)。因此，現(xiàn)在還沒有理論支持MOND的結(jié)果。那么，主流物理的重點搜索范圍放在以粒子為基礎(chǔ)的暗物質(zhì)候選者身上。三、基于粒子的暗物質(zhì)探索在此，我們將回顧主流物理所開展的基于粒子的暗物質(zhì)探索及其搜索途徑。1. 大型強子對撞機LHC的2 TeV實驗，已經(jīng)排除了所有的SUSY粒子。它也排除了大質(zhì)量弱相互作用WIMP粒子（如LUX和PANDAx，2017），這些數(shù)據(jù)的的搜索現(xiàn)在已經(jīng)非常接近中

6、微子可能出現(xiàn)的底部。2最新的天文數(shù)據(jù)幾乎排除了無菌中微子。而且，最新的數(shù)據(jù)也幾乎完全排除了“大爆炸核合成（BBN）”作為暗物質(zhì)。BBN的適合分析說明中微子是狄拉克費米子（沒有一個大規(guī)模的合作伙伴）。如果中微子是馬約拉納粒子（要求有一個隱藏的巨大的合作伙伴，如無菌中微子），BBN沒有符合觀測的數(shù)據(jù)。參見：/pdf/1709.01211.pdf。在米諾斯，米諾斯+反應(yīng)器實驗排除了惰性中微子（/abs/1710.06488）；最近的LIGO 中子星碰撞的中微子參數(shù)空間，（/abs/1710.06370）。

7、2. 排除軸子假設(shè)。4. 探測未知粒子運行所有可能躲藏的地方，排除任何大質(zhì)量弱相互作用粒子（WIMPs）（非對稱），看到pico-60數(shù)據(jù)。5. 沒有發(fā)現(xiàn)暗黑的光子/2017/11/08/scientists-narrow-search-dark-photon-dark-matter/?！疤綔y器中暗光子的特征是極其簡單的：一個高能光子，沒有任何其他活動?！卑岛诠庾右脖挥脕斫忉寴?biāo)準(zhǔn)模型中觀察介子自旋的性質(zhì)和它的預(yù)測值之間的差異。最新結(jié)果：“基于BaBar規(guī)則的這些暗黑光子理論作為G-2異常解釋，有效地關(guān)閉這個窗口。”日本的一個實驗，類似于BaBar

8、的升級，叫Belle II，將在明年開始運行?！白罱K，Belle II將產(chǎn)生高于BaBar統(tǒng)計的100倍的數(shù)據(jù)?！边€有，2014年基本排除了以前假設(shè)的冷暗物質(zhì)(CDM， CDM+ )、暖暗物質(zhì) (WDM) 、自相互作用暗物質(zhì) (SIDM) 。這些都是廢棄、過時了的暗物質(zhì)候選者。關(guān)于基于粒子的暗物質(zhì)探索問題的更詳細文獻和數(shù)據(jù)將在附錄中列出。四、相似的實驗與理論思考“悟空”（DAMPE）實驗類似于丁肇中的阿爾法磁譜儀AMS02 ，但“悟空”（DAMPE）比AMS02 具有更高的靈敏度和探測能力。然而，阿爾法磁譜儀AMS02 的經(jīng)驗可以為“悟空”數(shù)據(jù)分析提供一些啟示。從阿爾法磁譜儀AMS02 可以看

9、到兩點（2013和2015）：1.  過量的正電子和反質(zhì)子。2.  數(shù)據(jù)的大幅度下降拐點（尤其是正電子）。然而，這些正電子過剩和大傾角被排除了由暗物質(zhì)DM衰變中產(chǎn)生的可能。再次，反質(zhì)子過剩的阿爾法磁譜儀AMS02 可以由已知的宇宙的過程解釋。（參見https:/home.cern/about/updates/2017/03/cosmic-collisions-lhcb-experiment）。從而阿爾法磁譜儀AMS02 的這種反質(zhì)子數(shù)據(jù)也排除了是暗物質(zhì)的可能。有很多原因，排除阿爾法磁譜儀AMS02 系統(tǒng)數(shù)據(jù)的傾角。最重要的一點是，對于阿爾法磁譜儀AMS02發(fā)現(xiàn)暗物質(zhì)候選者

10、的理論基礎(chǔ)是SUSY，現(xiàn)在已經(jīng)排除了所有2 TeV的SUSY粒子。從而注定AMS02發(fā)現(xiàn)暗物質(zhì)的機會很小很小，可以說一定會失敗！因此，雖然“悟空”發(fā)現(xiàn)了比阿爾法磁譜儀數(shù)據(jù)更高的能量（1.4 TeV）數(shù)據(jù)，它將無法超越和擺脫已知的超對稱約束，除非它是基于一個新的非超對稱物的候選者的理論。也就是說，即使“悟空”最新發(fā)現(xiàn)的數(shù)據(jù)突出點完成統(tǒng)計學(xué)分析和確認，我們?nèi)匀恍枰碌睦碚搧斫忉屵@種異常性態(tài)要求。其中一個例子就是費米神秘伽瑪射線信號，它們在暗物質(zhì)湮滅的源頭基本上被排除了，發(fā)現(xiàn)毫秒脈沖星是這個神秘伽瑪射線信號源。參見：“在銀河內(nèi)部解決射線點源的證據(jù)?！保?016年2月3日，參見https:/arxiv

11、.org/abs/1506.05124）。五、最后的理論檢驗當(dāng)我們祝賀“悟空”取得的成就，我們必須敦促中國理論物理學(xué)家繼續(xù)努力，加班加點找出一個新的理論基礎(chǔ)，而不是用SUSY來解釋這一新的發(fā)現(xiàn)?，F(xiàn)在，這個宇宙的組成現(xiàn)在已經(jīng)被黑暗能量調(diào)查和普朗克CMB（2013和2015）數(shù)據(jù)所確定（見上、下圖）。 也就是說，新的暗物質(zhì)理論必須得出這個客觀觀測結(jié)論，這是對任何新的暗物質(zhì)理論的最后檢驗。六、結(jié)束語無論什么樣的暗物質(zhì)理論，必須滿足與這個宇宙的客觀觀測數(shù)據(jù)相匹配。這是檢驗這個科學(xué)理論的試金石。悟空衛(wèi)星、阿爾法磁譜儀AMS02和未來其他科學(xué)探測儀器所發(fā)現(xiàn)的這個宇宙世界的暗物質(zhì)、暗能量、宇宙學(xué)常

12、數(shù)、粒子精細結(jié)構(gòu)常數(shù)等客觀數(shù)據(jù)，將進一步推動人類對這個宇宙的認識走向更加深入透徹，甚至是徹底革命性的更新。二十一世紀(jì)物理世界上空的兩朵暗云必將煙消云散。附1：于2016年8月6日在人民大會堂，我與原全國青聯(lián)朋友中國科學(xué)院院長書記白春禮院士有過一個簡短交談，我告訴了他我們有了重要成果，并寫上了我們的網(wǎng)址：，我要他關(guān)注。我還告訴他我們曾在全國青聯(lián)科學(xué)組，我們青聯(lián)朋友一起開過很多次會。8月6日 我與原全國青聯(lián)朋友中國科學(xué)院院長書記白春禮院士交流附2：附錄 國外暗物質(zhì)粒子探測參考資料             Appendi

13、x:* Exclusions from the LHC. /abs/1709.02304  and/abs/1510.01516* Exclusions from Xenon-100 /abs/1709.02222* Exclusions of Charming Dark Matter theories. /abs/1709.01930* Theodorus Maria Nieuwenhuizen “Subjectin

14、g dark matter candidates to the cluster test” (October 3, 2017, see /abs/1710.01375 ):Galaxy clusters, employed by Zwicky to demonstrate the existence of dark matter, pose new stringent tests. If merging clusters demonstrate that dark matter is self-interacting with cross s

15、ection /m2 cm2/gr, MACHOs, primordial black holes and light axions that build MACHOs are ruled out as cluster dark matter. Recent strong lensing and X-ray gas data of the quite relaxed and quite spherical cluster A1835 allow to test the cases of dark matter with Maxwell-Boltzmann, Bose-Einstein and

16、Fermi-Dirac distribution, next to Navarro-Frenck-White profiles. Fits to all these profiles are formally rejected at over 5, except in the fermionic situation. The interpretation in terms of (nearly) Dirac neutrinos with mass of 1.61+0.190.30 eV/c2 is consistent with results on the cluster A1689, wi

17、th the WMAP, Planck and DES dark matter fractions and with the nondetection of neutrinoless double -decay. The case will be tested in the 2018 KATRIN experiment.A variety of searches for sterile neutrinos have also ruled out this possibility in the relevant mass range. See, e.g., https:/arxiv.o

18、rg/abs/1710.06488  and* Exclusions for Axion Dark Matter: Renée Hlozek, David J. E. Marsh, Daniel Grin “Using the Full Power of the Cosmic Microwave Background to Probe Axion Dark Matter” (August 18, 2017, see /abs/1708.05681 ).* Combined direct dark matter d

19、etection exclusions./abs/1708.04630  and /abs/1707.01632* Exclusions based on non-detection of annihilations in dwarf galaxies./abs/1708.04858* Primordial black hole exclusions. /abs/1301.4984* Daniele Gaggero, et al

20、., “Searching for Primordial Black Holes in the radio and X-ray sky” (see /abs/1612.00457 ). Abstract:We model the accretion of gas on to a population of massive primordial black holes in the Milky Way, and compare the predicted radio and X-ray emission with observational d

21、ata. We show that under conservative assumptions on the accretion process, the possibility that O(10) M primordial black holes can account for all of the dark matter in the Milky Way is excluded at 4 by a comparison with the VLA radio catalog at 1.4 GHz, and at more than 5 by a comparison with the N

22、uSTAR X-ray catalog (10 40 keV). We also propose a new strategy to identify such a population of primordial black holes with more sensitive future radio and X-ray surveys.* Tight Warm Dark Matter parameter exclusions,* More Warm Dark Matter parameters exclusions: Simon Birrer, Adam Amara, and Alexan

23、dre Refregier, “Lensing substructure quantification in RXJ1131-1231: A 2 keV lower bound on dark matter thermal relict mass” (January 31, 2017, see/abs/1702.00009 ).We study the substructure content of the strong gravitational lens RXJ1131-1231through a forward modelling approac

24、h that relies on generating an extensive suite of realistic simulations. The statistics of the substructure population of halos depends on the properties of dark matter. We use a merger tree prescription that allows us to stochastically generate substructure populations whose properties depend on th

25、e dark matter particle mass. These synthetic halos are then used as lenses to produce realistic mock images that have the same features, e.g. luminous arcs, quasar positions, instrumental noise and PSF, as the data. By analyzing the data and the simulations in the same way, we are able to constrain

26、models of dark matter statistically using Approximate Bayesian Computing (ABC) techniques. This method relies on constructing summary statistics and distance measures that are sensitive to the signal being targeted. We find that using the HST data for RXJ we are able to rule out a warm dark matter t

27、hermal relict mass below 2 keV at the 2 sigma confidence level.* Paolo Salucci and Nicola Turini, “Evidences for Collisional Dark Matter In Galaxies?” (July 4, 2017, see /abs/1707.01059 ). Abstract:The more we go deep into the knowledge of the dark component which embeds th

28、e stellar component of galaxies, the more we realize the profound interconnection between them. We show that the scaling laws among the structural properties of the dark and luminous matter in galaxies are too complex to derive from two inert components that just share the same gravitational field.

29、In this paper we review the 30 years old paradigm of collisionless dark matter in galaxies. We found that their dynamical properties show strong indications that the dark and luminous components have interacted in a more direct way over a Hubble Time. The proofs for this are the presence of central

30、cored regions with constant DM density in which their size is related with the disk length scales. Moreover we find that the quantity DM(r,L,RD)(r,L,RD) shows, in all objects, peculiarities very hardly explained in a collisionless DM scenario.* Dark matter distributions have to closely track baryon

31、distributions, even though there is no viable mechanism to do so: Edo van Uitert, et al., “Halo ellipticity of GAMA galaxy groups from KiDS weak lensing” (October 13, 2016, see/abs/1610.04226 ).* One of the more successful recent efforts to reproduce the baryonic Tully-Fischer r

32、elation with CDM models is L.V. Sales, et al., “The low-mass end of the baryonic Tully-Fisher relation” (February 5, 2016, see/abs/1602.02155 ). It explains:The literature is littered with failed attempts to reproduce the Tully-Fisher relation in a cold dark matter-dominated uni

33、verse. Direct galaxy formation simulations, for example, have for many years consistently produced galaxies so massive and compact that their rotation curves were steeply declining and, generally, a poor match to observation. Even semi-analytic models, where galaxy masses and sizes can be adjusted t

34、o match observation, have had difficulty reproducing the Tully-Fisher relation, typically predicting velocities at given mass that are significantly higher than observed unless somewhat arbitrary adjustments are made to the response of the dark halo.The paper manages to simulate the Tully-Fisher rel

35、ation only with a model that has sixteen parameters carefully “calibrated to match the observed galaxy stellar mass function and the sizes of galaxies at z = 0” and “chosen to resemble the surroundings of the Local Group of Galaxies”, however, and still struggles to reproduce the one parameter fits

36、of the MOND toy-model from three decades ago. Any data set can be described by almost any model so long as it has enough adjustable parameters.* Dark matter cant explain bulge formation in galaxies: Alyson M. Brooks, Charlotte R. Christensen, “Bulge Formation via Mergers in Cosmological Simulations”

37、 (12 Nov 2015, see /abs/1511.04095 ).We also demonstrate that it is very difficult for current stellar feedback models to reproduce the small bulges observed in more massive disk galaxies like the Milky Way. We argue that feedback models need to be improved, or an additiona

38、l source of feedback such as AGN is necessary to generate the required outflows.* Baryon effects cant save cold dark matter models./abs/1706.03324* Cold dark matter models dont explain the astronomy data.Evidence that Cold Dark Matter (CDM), CDM+ baryons and its proposed tailored cur

39、es do not work in galaxies is staggering, and the CDM wimps (DM particles heavier than 1 GeV) are strongly disfavoured combining theory with galaxy astronomical observations.* As of 2014, a review article ruled out pretty much all cold dark matter models except “warm dark matter” (WDM) (at a keV sca

40、le mass that is at the bottom of the range permitted by the lamdaCDM model) and “self-interacting dark matter” (SIDM) (which escapes problems that otherwise plague cold dark matter models with a fifth force that only acts between dark matter particles requiring at least a beyond the Standard Model f

41、ermion and a beyond the Standard Model force carried by a new massive boson with a mass on the order of 1-100 MeV). Alyson Brooks, “Re-Examining Astrophysical Constraints on the Dark Matter Model” (July 28, 2014, see /abs/1407.7544 ). As other more recent links cited here n

42、ote, collisionless WDM and pretty much all SIDM models have since been ruled out.* Proposed warm dark matter annihilation signals also turned out to be false alarms. /abs/1408.1699  and /abs/1408.4115 .* The bounds on the minimum dark matter m

43、ean lifetime of 3.57×1024 seconds. This is roughly 1017 years. By comparison the age of the universe is roughly 1.38 x 109 years. This means that dark matter (if it exists) is at least as stable as anything other than a proton, which has an experimentally determined mean lifetime of at least 10

44、33 years./abs/1504.01195 . This means that all dark matter candidates that are not perfectly stable or at least metastable are ruled out. Decaying dark matter and dark matter with any significant annihilation cross section are inconsistent with observation.* Torsten Bringmann, e

45、t al., “Strong constraints on self-interacting dark matter with light mediators” (December 2, 2016, see /abs/1612.00845). Abstract:Coupling dark matter to light new particles is an attractive way to combine thermal production with strong velocity-dependent self-interactions. Her

46、e we point out that in such models the dark matter annihilation rate is generically enhanced by the Sommerfeld effect, and we derive the resulting constraints from the Cosmic Microwave Background and other indirect detection probes. For the frequently studied case of s-wave annihilation these constr

47、aints exclude the entire parameter space where the self-interactions are large enough to address the small-scale problems of structure formation.The conclusion of the paper notes that:Models of DM with velocity-dependent self-interactions have recently received a great deal of attention for their po

48、tential to produce a number of interesting effects on astrophysical scales. We have shown in this Letter that these models face very strong constraints from the CMB and DM indirect detection. In the most natural realization of this scenario with a light vector mediator with kinetic mixing, these con

49、straints rule out the entire parameter space where the self-scattering cross section can be relevant for astrophysical systems. These bounds remain highly relevant for a number of generalizations of the scenario, such as a different dark sector temperature and different mediator branching ratios. Cl

50、early, future efforts to develop particle physics models for SIDM need to address these issues in order to arrive at models that provide a picture consistent with all observations in cosmology, astrophysics and particle physics.* Dark photon parameter space (the carrier boson of the SIDM models) is

51、also tightly constrained and all but ruled out. Yet, the properties a dark photon has to have, if there is one, are tightly experimentally established based upon cluster dynamics. /abs/1504.06576 .* The Bullet Cluster is a huge problem for DM. Jounghun Lee, Eiichiro Komatsu

52、, “Bullet Cluster: A Challenge to LCDM Cosmology” (May 22, 2010, see/abs/1003.0939 ). Later published in Astrophysical Journal 718 (2010) 60-65. Abstract:To quantify how rare the bullet-cluster-like high-velocity merging systems are in the standard LCDM cosmology, we use a large

53、-volume 27 (Gpc/h)3 MICE simulation to calculate the distribution of infall velocities of subclusters around massive main clusters. The infall-velocity distribution is given at (1-3)R_200 of the main cluster (where R_200 is similar to the virial radius), and thus it gives the distribution of realist

54、ic initial velocities of subclusters just before collision. These velocities can be compared with the initial velocities used by the non-cosmological hydrodynamical simulations of 1E0657-56 in the literature. The latest parameter search carried out recently by Mastropietro and Burkert showed that the initial