主流物理界对暗物质研究的现状

李小坚  龚天任

本文简要介绍主流物理界对暗物质研究和理解的现状。

一、 引言

最近关于“悟空”(DAMPE)卫星数据的好消息,给中国科学界带来了一次狂欢。媒体纷纷报道,其中有两点共识:

第一,暗物质的存在是毫无疑问的,暗物质与可见物质的比率大约在5比1之间。

第二,迄今为止没有人知道这个问题的答案:暗物质是什么?

是的,以上这两点基本上是正确的。

暗物质是什么?在主流物理学界没有人知道答案!

中国科学院院长白春礼,谈暗物质的视频介绍:
暗物质是什么?中科院院长告诉你_网易新闻 http://news.163.com/17/1130/11/D4G3RP0I00018AOQ.html

白春礼院士介绍,这是令世界物理主流困惑不解,更是令全世界普通民众迷惑的大问题!

最终,全球科学界将通过科学的方法一一排除那些疑似暗物质的候选者,确定{暗物质不是什么}。

的确,主流科学在{暗物质不是什么}已经取得许多成果。但关键问题是{暗物质是什么?},这个问题必须要有理论突破!

因此,我们可以从网上看到全球科学界正在努力,试图揭开这个谜底。{暗物质不是什么} 与{暗物质是什么?}成为全球人类的热点问题!

那么,我们现在来看一看,国际主流物理界关于暗物质问题的探索情况。

二、主流物理界对暗物质的认识

1.已知的暗物质

国际主流界公认的已知的暗物质有两种:1)中微子,2)黑洞。

然而,这两种已知的暗物质不能解释全部整个暗物质。也就是说,还有其他的物质也扮演着暗物质的角色。事实上,在许多天体物理调查中,这两个已知的暗物质只占总暗物质的很小的百分比(小于1%),见:“2017的暗能量调查”结果。

2. 我们先说黑洞

去年,以及今年LIGO多次发现双黑洞的合并凝聚,显示出宇宙中的黑洞密度很高,从而,似乎“黑洞暗物质假说”又死灰复燃。
宇宙中有两种方式产生黑洞。

第一种,黑洞就是一颗恒星的残余。这个恒星演变过程我们现在非常清楚地知道了解。我们还可以计算出每个星系中的黑洞数量。对于银河系,它有大约300万个黑洞,每个黑洞的平均质量为10个太阳质量。这300万个黑洞中的暗物质约占银河系总质量的0.001%。显然,这一种黑洞不能成为整个宇宙暗物质的候选者。

第二种,可能有在大爆炸期间产生的一些原始黑洞。它们携带的质量,大约可以从0.1到10亿个太阳质量不等。此外,我们不知道这些黑洞的密度。也就是说,它很有可能代表整个宇宙的暗物质。然而,通过分析LIGO的数据,给出了否定的回答:没有!
原始黑洞无法解释宇宙全部的暗物质。也就是说,一定还有其他东西扮演暗物质的角色。

参见:LIGO不硬气:原始黑洞、暗物质和Ia型超新星的引力透镜效应。(https://arxiv.org/abs/1712.02240)。

3.其他暗物质候选者,包括中微子
在主流物理学,基本上还有这两类暗物质候选者:1)不基于粒子的任何暗物质,如修改引力定律(MOND)。2)以粒子为基础的暗物质候选者:一些未知的粒子,如弱互相质量粒子WIMP(例如,无菌中微子、轴子、暗光子等);

2017年10月16日宣布的LIGO双中子星合并,它几乎完全排除了MOND存在的证据。参见{ gw170817暗物质仿真器(https://arxiv.org/abs/1710.06168)}。

外,我国发射的 “悟空”(DAMPE)的数据,还没有发现任何MOND关联的证据。因此,现在还没有理论支持MOND的结果

那么,主流物理的重点搜索范围放在以粒子为基础的暗物质候选者身上。

三、基于粒子的暗物质探索

在此,我们将回顾主流物理所开展的基于粒子的暗物质探索及其搜索途径。

1. 大型强子对撞机LHC的2 TeV实验,已经排除了所有的SUSY粒子。它也排除了大质量弱相互作用WIMP粒子(如LUX和PANDAx,2017),这些数据的的搜索现在已经非常接近中微子可能出现的底部。

SC-13

2.最新的天文数据几乎排除了无菌中微子。

而且,最新的数据也几乎完全排除了“大爆炸核合成(BBN)”作为暗物质。BBN的适合分析说明中微子是狄拉克费米子(没有一个大规模的合作伙伴)。如果中微子是马约拉纳粒子(要求有一个隐藏的巨大的合作伙伴,如无菌中微子),BBN没有符合观测的数据。
参见:https://arxiv.org/pdf/1709.01211.pdf。
在米诺斯,米诺斯+反应器实验排除了惰性中微子(https://arxiv.org/abs/1710.06488);
最近的LIGO {中子星碰撞的中微子参数空间,(https://arxiv.org/abs/1710.06370)}。

3. 排除轴子假设。

AXon
4. 探测未知粒子运行所有可能躲藏的地方,排除任何大质量弱相互作用粒子(WIMPs)(非对称),看到pico-60数据。

PICO60
5. 没有发现暗黑的光子
http://newscenter.lbl.gov/2017/11/08/scientists-narrow-search-dark-photon-dark-matter/。

darkphoton

“探测器中暗光子的特征是极其简单的:一个高能光子,没有任何其他活动。”

暗黑光子也被用来解释标准模型中观察μ介子自旋的性质和它的预测值之间的差异。

最新结果:“基于BaBar规则的这些暗黑光子理论作为G-2异常解释,有效地关闭这个窗口。”

日本的一个实验,类似于BaBar的升级,叫Belle II,将在明年开始运行。“最终,Belle II将产生高于BaBar统计的100倍的数据。”

还有,2014年基本排除了以前假设的冷暗物质(ΛCDM, CDM+ )、暖暗物质 (WDM) 、自相互作用暗物质 (SIDM) 。这些都是废弃、过时了的暗物质候选者。

关于基于粒子的暗物质探索问题的更详细文献和数据将在附录中列出。

四、相似的实验与理论思考

“悟空”(DAMPE)实验类似于丁肇中的阿尔法磁谱仪AMS02 ,但“悟空”(DAMPE)比AMS02 具有更高的灵敏度和探测能力。然而,阿尔法磁谱仪AMS02 的经验可以为“悟空”数据分析提供一些启示。

从阿尔法磁谱仪AMS02 可以看到两点(2013和2015):

SC-14

1.  过量的正电子和反质子。

2.  数据的大幅度下降拐点(尤其是正电子)。

然而,这些正电子过剩和大倾角被排除了由暗物质DM衰变中产生的可能。
再次,反质子过剩的阿尔法磁谱仪AMS02 可以由已知的宇宙的过程解释。
(参见https://home.cern/about/updates/2017/03/cosmic-collisions-lhcb-experiment)。
从而阿尔法磁谱仪AMS02 的这种反质子数据也排除了是暗物质的可能。

csc-anti-position
有很多原因,排除阿尔法磁谱仪AMS02 系统数据的倾角。最重要的一点是,对于阿尔法磁谱仪AMS02发现暗物质候选者 的理论基础是SUSY,现在已经排除了所有2 TeV的SUSY粒子。从而注定AMS02发现暗物质的机会很小很小,可以说一定会失败!

因此,虽然“悟空”发现了比阿尔法磁谱仪数据更高的能量(1.4 TeV)数据,它将无法超越和摆脱已知的超对称约束,除非它是基于一个新的非超对称物的候选者的理论。

也就是说,即使“悟空”最新发现的数据突出点完成统计学分析和确认,我们仍然需要新的理论来解释这种异常性态要求。其中一个例子就是费米神秘伽玛射线信号,它们在暗物质湮灭的源头基本上被排除了,发现毫秒脉冲星是这个神秘伽玛射线信号源。参见:“在银河内部解决γ射线点源的证据。”(2016年2月3日,参见https://arxiv.org/abs/1506.05124)。

五、最后的理论检验

当我们祝贺“悟空”取得的成就,我们必须敦促中国理论物理学家继续努力,加班加点找出一个新的理论基础,而不是用SUSY来解释这一新的发现。

plk2013

现在,这个宇宙的组成现在已经被黑暗能量调查和普朗克CMB(2013和2015)数据所确定(见上、下图)。

UNIVERS-CONTENTS-11

 

eggcarton204
也就是说,新的暗物质理论必须得出这个客观观测结论,这是对任何新的暗物质理论的最后检验。

六、结束语

无论什么样的暗物质理论,必须满足与这个宇宙的客观观测数据相匹配。这是检验这个科学理论的试金石。

悟空卫星、阿尔法磁谱仪AMS02和未来其他科学探测仪器所发现的这个宇宙世界的暗物质、暗能量、宇宙学常数、粒子精细结构常数等客观数据,将进一步推动人类对这个宇宙的认识走向更加深入透彻,甚至是彻底革命性的更新。

二十一世纪物理世界上空的两朵暗云必将烟消云散。

参考文献:

1. 蔡荣根  周宇峰 ,暗物质与暗能量研究新进展
中国科学院理论物理研究所, 北京 100190 ,2010,03

中图分类号: O41 文献标识码: A
文章编号: 10092412( 2010) 03000307
DO I: 10. 3969 /.j issn. 1009
2412. 2010. 03. 001

中国基础科学  综述评述

注1:最近,蔡荣根院士报告表明:暗物质模型有上百种!

但问题是:哪一个是中国人提出的?有何验证?

附1:

于2016年8月6日在人民大会堂,我与原全国青联朋友中国科学院院长、书记白春礼院士有过一个简短交谈,我告诉了他我们有了重要成果,并写上了我们的网址:www.pptv1.com,我要他关注。我们曾在全国青联科学组,我们青联朋友一起开过很多次会。

8月6日 我与原全国青联朋友中国科学院院长书记白春礼院士交流
附2:附录
                                     Appendix:

* Exclusions from the LHC. https://arxiv.org/abs/1709.02304  andhttps://arxiv.org/abs/1510.01516

* Exclusions from Xenon-100 https://arxiv.org/abs/1709.02222

* Exclusions of Charming Dark Matter theories. https://arxiv.org/abs/1709.01930

* Theodorus Maria Nieuwenhuizen “Subjecting dark matter candidates to the cluster test” (October 3, 2017, see https://arxiv.org/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 section σ/m∼2 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 Fermi-Dirac distribution, next to Navarro-Frenck-White profiles. Fits to all these profiles are formally rejected at over 5σ, except in the fermionic situation. The interpretation in terms of (nearly) Dirac neutrinos with mass of 1.61+0.19−0.30 eV/c2 is consistent with results on the cluster A1689, with the WMAP, Planck and DES dark matter fractions and with the nondetection of neutrinoless double β-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.org/abs/1710.06488  andhttp://iopscience.iop.org/article/10.1088/1742-6596/718/3/032008/pdf

* 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 https://arxiv.org/abs/1708.05681 ).

* Combined direct dark matter detection exclusions.https://arxiv.org/abs/1708.04630  and https://arxiv.org/abs/1707.01632

* Exclusions based on non-detection of annihilations in dwarf galaxies.https://arxiv.org/abs/1708.04858

* Primordial black hole exclusions. https://arxiv.org/abs/1301.4984

* Daniele Gaggero, et al., “Searching for Primordial Black Holes in the radio and X-ray sky” (see https://arxiv.org/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 data. 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 4σ by a comparison with the VLA radio catalog at 1.4 GHz, and at more than 5σ by a comparison with the NuSTAR 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,https://arxiv.org/pdf/1704.01832.pdf

* More Warm Dark Matter parameters exclusions: Simon Birrer, Adam Amara, and Alexandre Refregier, “Lensing substructure quantification in RXJ1131-1231: A 2 keV lower bound on dark matter thermal relict mass” (January 31, 2017, seehttps://arxiv.org/abs/1702.00009 ).

We study the substructure content of the strong gravitational lens RXJ1131-1231through a forward modelling approach 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 the 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 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 thermal 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 https://arxiv.org/abs/1707.01059 ). Abstract:

The more we go deep into the knowledge of the dark component which embeds the 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. 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 cored regions with constant DM density in which their size is related with the disk length scales. Moreover we find that the quantity ρDM(r,L,RD)ρ⋆(r,L,RD) shows, in all objects, peculiarities very hardly explained in a collisionless DM scenario.

* Dark matter distributions have to closely track baryon 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, seehttps://arxiv.org/abs/1610.04226 ).

* One of the more successful recent efforts to reproduce the baryonic Tully-Fischer relation with CDM models is L.V. Sales, et al., “The low-mass end of the baryonic Tully-Fisher relation” (February 5, 2016, seehttps://arxiv.org/abs/1602.02155 ). It explains:

[T]he literature is littered with failed attempts to reproduce the Tully-Fisher relation in a cold dark matter-dominated universe. 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 to 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 relation 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 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 can’t explain bulge formation in galaxies: Alyson M. Brooks, Charlotte R. Christensen, “Bulge Formation via Mergers in Cosmological Simulations” (12 Nov 2015, see https://arxiv.org/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 additional source of feedback such as AGN is necessary to generate the required outflows.

* Baryon effects can’t save cold dark matter models.https://arxiv.org/abs/1706.03324

* Cold dark matter models don’t explain the astronomy data.https://arxiv.org/pdf/1305.7452v2.pdf

Evidence that Cold Dark Matter (ΛCDM), CDM+ baryons and its proposed tailored cures 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 scale 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 fermion 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 https://arxiv.org/abs/1407.7544 ). As other more recent links cited here note, 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. https://arxiv.org/abs/1408.1699  and https://arxiv.org/abs/1408.4115 .

* The bounds on the minimum dark matter mean lifetime of 3.57×10^24 seconds. This is roughly 10^17 years. By comparison the age of the universe is roughly 1.38 x 10^9 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 10^33 years.https://arxiv.org/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, et al., “Strong constraints on self-interacting dark matter with light mediators” (December 2, 2016, see https://arxiv.org/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. Here 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 constraints 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 potential 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 constraints 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. Clearly, 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 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. https://arxiv.org/abs/1504.06576 .

* The Bullet Cluster is a huge problem for DM. Jounghun Lee, Eiichiro Komatsu, “Bullet Cluster: A Challenge to LCDM Cosmology” (May 22, 2010, seehttps://arxiv.org/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-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 realistic 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 velocity of 3000 km/s at about 2R_{200} is required to explain the observed shock velocity, X-ray brightness ratio of the main and subcluster, and displacement of the X-ray peaks from the mass peaks. We show that such a high infall velocity at 2R_{200} is incompatible with the prediction of a LCDM model: the probability of finding 3000 km/s in (2-3)R_{200} is between 3.3X10^{-11} and 3.6X10^{-9}. It is concluded that the existence of 1E0657-56 is incompatible with the prediction of a LCDM model, unless a lower infall velocity solution for 1E0657-56 with < 1800 km/s at 2R_{200} is found.

*Garry W. Angus and Stacy S. McGaugh, “The collision velocity of the bullet cluster in conventional and modified dynamics” (September 2, 2007, seehttps://arxiv.org/abs/0704.0381 ) published at MNRAS.

We consider the orbit of the bullet cluster 1E 0657-56 in both CDM and MOND using accurate mass models appropriate to each case in order to ascertain the maximum plausible collision velocity. Impact velocities consistent with the shock velocity (~ 4700km/s) occur naturally in MOND. CDM can generate collision velocities of at most ~ 3800km/s, and is only consistent with the data provided that the shock velocity has been substantially enhanced by hydrodynamical effects.

* El Gordo poses similar problems for dark matter models. Sandor M. Molnar, Tom Broadhurst. “A HYDRODYNAMICAL SOLUTION FOR THE “TWIN-TAILED” COLLIDING GALAXY CLUSTER “EL GORDO”, see https://arxiv.org/abs/1405.2617. The Astrophysical Journal, 2015; 800 (1): 37 DOI: 10.1088/0004-637X/800/1/37

* Axion fuzzy dark matter ruled out: Vid Iršič, Matteo Viel, Martin G. Haehnelt, James S. Bolton, George D. Becker. “First Constraints on Fuzzy Dark Matter from Lyman-α Forest Data and Hydrodynamical Simulations”, seehttps://arxiv.org/abs/1703.04683 . Physical Review Letters, 2017; 119 (3) DOI: 10.1103/PhysRevLett.119.031302

 

发表评论

电子邮件地址不会被公开。