EDGES 21厘米信号揭示新边界：ALP与激发暗物质的约束

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本文探讨了边缘21厘米吸收信号对轴子（Axion-Like Particles, ALPs）和激发的暗物质的限制与影响。来自EDGES实验的最新21厘米吸收信号观测为研究早期宇宙的物理过程提供了宝贵的线索。ALPs是一种理论上的轻粒子，它们在某些物理模型中扮演着暗物质的角色，而激发的暗物质则涉及暗物质粒子之间发生非标准相互作用。研究者们通过模拟这些模型产生的气体介质中的能量注入，特别是利用了莱曼-α光子的强度和电离辐射产生的电子发射率数据，对ALPs的特性进行了细致的约束。他们将这些约束与当前已知的能量注入范围（10.2电子伏特至50千电子伏特）进行了对比，发现他们的分析结果在这一能量区间内提供了更严格的限制。这种高精度的测量对于理解ALPs作为潜在暗物质成分的可能性具有重要意义。此外，文章还指出，当考虑到一个标准的软辐射背景温度时，之前在某些暗物质模型中观察到的3.5千电子伏特光子信号的解释在95%置信水平下被排除。这进一步支持了对暗物质性质和宇宙早期环境的深入探索，暗示可能需要重新审视关于暗物质粒子与普通物质相互作用的传统假设。这项工作不仅深化了我们对21厘米吸收线的理解，而且对暗物质研究领域提出了新的挑战和可能性，推动了理论模型与观测数据之间的桥梁建设。它强调了现代实验技术在揭示宇宙奥秘中的关键作用，并促进了对基本粒子物理和宇宙学问题的前沿研究。

Physics Letters B 785 (2018) 429–433

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Constraints on ALPs and excited dark matter from the EDGES 21 cm

absorption signal

Andi Hektor

, Gert Hütsi

a,b,∗

, Luca Marzola

, Ville Vaskonen

Laboratory of High Energy and Computational Physics, National Institute of Chemical Physics and Biophysics, Rävala pst. 10, 10143 Tallinn, Estonia

Tartu Observatory, University of Tartu, Observatooriumi 1, 61602 Tõravere, Estonia

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

Article history:

Received

4 June 2018

Received

in revised form 3 July 2018

Accepted

4 September 2018

Available

online 6 September 2018

Editor: A.

Ringwald

The recent observation of the 21 cm absorption signal by the EDGES experiment provides a new

observational window into the dynamics of the young Universe. Based on this result, we constrain the

properties of ALPs and excited dark matter via the energy injections into the gaseous medium that

these models produce. In particular, we derive bounds that outperform the present constraints for energy

injections in the 10.2 eV to 50 keV range by analysing the intensity of Lyman-α photons and the electron

emissivity produced by ionising radiation. Our results also show that once the standard temperature of

the soft radiation background is assumed, the explanations of the observed 3.5 keV photon signal within

the considered dark matter model are excluded at 95% conﬁdence level.

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

1. Introduction

The recent detection of the 21 cm spectrum by the EDGES

experiment [1]presents a ﬁrst insight into the dynamics of the

Dark Ages of the Universe, close to the onset of star formation.

Within CDM, the observed absorption feature is explained by the

Wouthuysen–Field effect [2,3], after the ﬁrst stars produced a sig-

niﬁcant

population of Lyman-α photons at z ∼ 20. The effect of

this energetic radiation is then to decouple the hydrogen spin tem-

perature

from the soft radiation temperature that characterises the

redshifted CMB background, forcing it to converge to the lower ki-

netic

temperature of the gas.

Whereas

the redshift of the observed signal agrees with the

theoretical predictions, the measured magnitude of the absorption

feature greatly exceeds the CDM expectations, consequently rais-

ing

the problem of its origin. Explanations of the EDGES result

proposed in literature invoke either new mechanisms for cooling

the gaseous medium [4–16]or the presence of an additional soft

photon component [17–22]. However, the mechanism beyond the

anomaly remains to-date unclear. Furthermore, the signiﬁcance of

the measurement and the treatment of the foregrounds is cur-

rently

under debate [23,24].

Corresponding author.

E-mail

addresses: andi.hektor@cern.ch (A. Hektor), gert.hutsi@to.ee (G. Hütsi),

luca.marzola@cern.ch (L. Marzola), ville.vaskonen@kbﬁ.ee (V. Vaskonen).

In spite of its possible origin, a conﬁrmation of the EDGES

measurement would provide a new observable capable of probing

the dynamics of the young Universe. As an example, the mea-

sured

absorption proﬁle strongly constrains the presence of addi-

tional

mechanisms resulting in Lyman-α radiation at z  20, which

would otherwise induce earlier absorption signals. At higher ener-

gies,

the 21 cm spectrum constrains instead possible energy injec-

tions

that would lead to ionizations and consequent heating of the

gaseous medium. These observations have been used in literature

to bound energy injections due to new physics processes [25–30],

the properties of the dark sector [31–33] and to investigate the

astrophysical consequences implied by the signal [34–37].

this Letter we adopt the same attitude and make use of

the EDGES results to investigate the properties of light dark mat-

ter

(DM) candidates that could result in energy injections in the

gaseous medium over the 10.2 eV to 50 keV range, a mass range

not considered by the above-cited papers. As concrete examples

we consider the case of axion-like particles (ALPs) [38] and of ex-

cited

DM [39], deriving the phenomenological consequences of the

EDGES measurement and comparing the resulting constraints to

the ones previously proposed in the literature [40,41]. Particular

attention is paid to the issue of the 3.5 keV line detected in galaxy

clusters [42,43], previously motivated both in excited DM [44] and

ALPs [45]models.

Our

analyses show that once a temperature of the soft radia-

tion

background in agreement with CDM is assumed, the con-

straints

resulting from the EDGES measurement outperform the

https://doi.org/10.1016/j.physletb.2018.09.009

0370-2693/

SCOAP

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