Contributions of dark matter annihilation to the global 21 cm spectrum observed by the EDGES experiment

Abstract

The EDGES experiment has observed an absorption feature in the global 21cm spectrum with a surprisingly large amplitude. These results can be explained by decreasing the kinetic temperature of baryons, which could be achieved through the scattering between the baryons and cold dark matter particles. It seems that the mostly researched dark matter annihilation model is not able to explain such a large amplitude, since the interactions between the particles produced by the dark matter annihilation and the particles that have been present in the Universe could increase the baryonic temperature. Recently, C. Feng and G. Holder have suggested that the large amplitude in the global 21cm spectrum could be produced by considering the possible excess of the early radio radiation. In this paper, we propose that the dark matter annihilation still works to explain the large amplitude observed by the EDGES experiment. By considering the possible excess of the early radio radiation, the large absorption amplitude in the global 21cm spectrum could be produced even including the dark matter annihilation. 2

Constraints on primordial black holes and curvature perturbations from the global 21-cm signal

“…[34]. The interactions, between the high energy photons emitted from accreting PBHs and the particles exist in the universe, lead to the changes of the degree of inoization and the thermal history of the IGM through heating, ionization and excitation [9,11,37,[48][49][50][51]. The changes of the degree of ionization (x e ) and the temperature of the IGM (T k ) with redshift are governed by the following equations [37,[48][49][50]:…”

“…P 10 is the radiative de-excitation rate due to Lyα photons [3,64]. The factor y c involves collisions between hydrogen atoms and other particles [9,61,[66][67][68],…”

“…When PBHs form, baryonic matter is accreted onto them with emition of high energy photons during the process of accretion [33][34][35][36]. The interactions between the high energy photons emitted from accreting PBHs and the particles existed in the universe will lead to the changes of the thermal history of the intergalactic medium (IGM), which will be reflected in the global 21-cm signal [9,11,[34][35][36][37][38][39].…”

21-cm observations and warm dark matter models

“…This makes the study of the 21-cm signal a promising tool to learn not only about cosmological parameters (see, e.g. [13][14][15]) but also about different properties of dark matter, including its decays and annihilations [16][17][18][19][20][21], dark matter-baryon interactions [22][23][24][25][26][27], and the formation of gravitationally bound structures [28][29][30][31][32][33].…”

Indirect detection of the partial p wave via the s wave in the annihilation cross section of dark matter

“…Recently the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) collaboration reported a measurement of the absorption of the redshifted 21 cm line from hydrogen gas at a redshift of z ≈ 15-20 [29]. This result can be interpreted as demonstrating a stronger absorption signal than standard astrophysical expectations, and has sparked a flurry of studies in the dark matter literature, including implications for dark matter-baryon couplings [30][31][32][33][34][35][36][37], dark matter annihilation [5,[38][39][40], decaying dark matter [40][41][42], primordial black holes [41,43], fuzzy dark matter [44], dark sectors [45][46][47][48], and noncold dark matter models including warm dark matter and axions [49][50][51][52][53][54].…”