暗物质模型：解决AMS-02 e±过量与伽马射线及CMB约束间的矛盾

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本文主要探讨了暗物质模型在解决宇宙射线(e±)过量现象与伽马射线和宇宙微波背景辐射(CMB)观测结果之间矛盾的关键角色。AMS-02实验观测到的高能量电子和正电子似乎可以由暗物质粒子的湮灭过程产生，这提供了一种潜在的暗物质解释。然而，这一理论面临挑战，因为暗物质湮灭截面若要解释CR e±过量，通常需要一个较大的值，而这与Fermi-LAT在矮星系观测到的低伽马射线信号以及普朗克卫星对CMB的精确测量结果相冲突，这些观测显示了较低的暗物质活动。为了缓解这种张力，研究者提出采用带有速度依赖的Breit-Wigner机制。这种机制假设暗物质粒子的湮灭截面在特定速度范围内表现出显著增强，当粒子的速度接近物理极点的共振状态时，其湮灭效率最大化。在银河系中，由于暗物质粒子速度较高，它们可能经历显著的湮灭，而在运动较慢的矮星系和大爆炸后早期的宇宙中，这种湮灭则会被抑制，从而避免对伽马射线和CMB观测结果产生过大的影响。作者通过对暗物质粒子的特性进行精细调整，特别是其湮灭截面的速度依赖性，找到了一个能同时解释AMS-02 CR e±过量数据、保持热历史遗留的暗物质密度，并且符合Fermi-LAT和Planck实验约束的参数区域。这个工作对于理解暗物质的本质及其在宇宙中的作用具有重要意义，因为它不仅提供了一个可能的解决方案，还揭示了暗物质与普通物质相互作用的复杂性，以及如何通过精细的理论模型来适应多源的观测数据。这篇论文在暗物质物理学领域具有重要的理论贡献，它展示了如何利用粒子物理学原理和观测数据，逐步缩小理论与实验之间的差距，推动了我们对暗物质的认识向更深层次发展。

Physics Letters B 773 (2017) 448–454

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

A dark matter model that reconciles tensions between the cosmic-ray

excess and the gamma-ray and CMB constraints

Qian-Fei Xiang

a,b

, Xiao-Jun Bi

, Su-Jie Lin

, Peng-Fei Yin

Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China

School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

a r t i c l e i n f o a b s t r a c t

Article history:

Received

7 August 2017

Received

in revised form 31 August 2017

Accepted

1 September 2017

Available

online 8 September 2017

Editor:

J. Hisano

The cosmic-ray (CR) e

excess observed by AMS-02 can be explained by dark matter (DM) annihilation.

However, the DM explanation requires a large annihilation cross section which is strongly disfavored

by other observations, such as the Fermi-LAT gamma-ray observation of dwarf galaxies and the Planck

observation of the cosmic microwave background (CMB). Moreover, the DM annihilation cross section

required by the CR e

excess is also too large to generate the correct DM relic density with thermal

production. In this work we use the Breit–Wigner mechanism with a velocity dependent DM annihilation

cross section to reconcile these tensions. If DM particles accounting for the CR e

excess with v ∼

O(10

−3

) are very close to a resonance in the physical pole case, their annihilation cross section in the

Galaxy reaches a maximal value. On the other hand, the annihilation cross section would be suppressed

for DM particles with smaller relative velocities in dwarf galaxies and at recombination, which may

affect the gamma-ray and CMB observations, respectively. We ﬁnd a proper parameter region that can

simultaneously explain the AMS-02 results and the thermal relic density, while satisfying the Fermi-LAT

and Planck constraints.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

1. Introduction

Astrophysics and cosmology observations reveal that the dom-

inant

matter component in the universe is dark matter (DM), but

the particle nature of DM remains unknown [1,2]. The existence

of DM cannot be explained within the framework of the standard

model (SM), and thus provides a hint of the physics beyond the

SM. Great efforts have been devoted to DM researches, including

collider detection, direct detection, and indirect detection experi-

ments.

particles can be traced by cosmic ray (CR) experiments

through their annihilation products from the Galaxy halo. The Al-

pha

Magnetic Spectrometer (AMS-02), launched in 2011, is able

to measure CR spectra with an unprecedented precision [3]. The

precise results released by AMS-02 have conﬁrmed the CR e

ex-

cess

above ∼ 10 GeV, which indicates the existence of exotic e

sources. Many astrophysical explanations have been proposed for

this excess, such as primary sources like pulsars [4–6], or the CR

interactions occurring around CR acceleration sources [7–10]. Inter-

E-mail address: yinpf@ihep.ac.cn (P.-F. Yin).

estingly, this excess can also be explained by DM annihilations/de-

cays

to charged leptons [11–17].

the other hand, DM particles would also generate high en-

ergy

photons associated with charged leptons. The related gamma-

ray

signatures can be signiﬁcant in systems with high DM densities

and low baryon densities, such as dwarf galaxies. However, the

Fermi-LAT observations do not ﬁnd such signatures, and set strong

constraints on the DM annihilation cross section [18–20]. Since the

large annihilation cross section required by the CR e

excess seems

not to be allowed by the Fermi-LAT constraints [17], the DM anni-

hilation

explanation is strongly disfavored.

Moreover,

the electromagnetically interacting particles gener-

ated

by DM annihilations at recombination could affect cosmic

microwave background (CMB) [21–27]. Precise measurements per-

formed

by WMAP [1] and recently by Planck [2] have been used

to set constraints on the DM energy injections and the DM anni-

hilation

cross sections for speciﬁed ﬁnal states. Compared to the

results from CR and gamma-ray observations, these constraints are

more stringent, and are free of some astrophysical uncertainties,

which arise from the large-scale structure formation, DM density

ﬁles and so on [26].

http://dx.doi.org/10.1016/j.physletb.2017.09.003

0370-2693/

SCOAP

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