A detailed exploration of the EDGES 21 cm absorption anomaly and axion-induced cooling. (arXiv:1812.03931v6 [hep-ph] UPDATED)
<a href="http://arxiv.org/find/hep-ph/1/au:+Li_C/0/1/0/all/0/1">Chuang Li</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Houston_N/0/1/0/all/0/1">Nick Houston</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Li_T/0/1/0/all/0/1">Tianjun Li</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Yang_Q/0/1/0/all/0/1">Qiaoli Yang</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Zhang_X/0/1/0/all/0/1">Xin Zhang</a>

The EDGES collaboration’s observation of an anomalously strong 21 cm
absorption feature around the cosmic dawn era has energised the cosmological
community by suggesting a novel signature of dark matter in the cooling of
cosmic hydrogen. In a recent letter we have argued that by virtue of the
ability to mediate cooling processes whilst in the condensed phase, a small
amount of axion dark matter can explain these observations within the context
of standard models of axions and axion-like particles. These axions and
axion-like particles (ALPs) can thermalize through gravitational
self-interactions and so eventually form a Bose-Einstein condensate (BEC),
whereupon large-scale long-range correlation can produce experimentally
observable signals such as these. In this context the EDGES best-fit result
favours an axion-like-particle mass in the (6, 400) meV range. Future
experiments and galaxy surveys, particularly the International Axion
Observatory (IAXO) and EUCLID, should have the capability to directly test this
scenario. In this paper, we will explore this mechanism in detail and give more
thorough computational details of certain key points.

The EDGES collaboration’s observation of an anomalously strong 21 cm
absorption feature around the cosmic dawn era has energised the cosmological
community by suggesting a novel signature of dark matter in the cooling of
cosmic hydrogen. In a recent letter we have argued that by virtue of the
ability to mediate cooling processes whilst in the condensed phase, a small
amount of axion dark matter can explain these observations within the context
of standard models of axions and axion-like particles. These axions and
axion-like particles (ALPs) can thermalize through gravitational
self-interactions and so eventually form a Bose-Einstein condensate (BEC),
whereupon large-scale long-range correlation can produce experimentally
observable signals such as these. In this context the EDGES best-fit result
favours an axion-like-particle mass in the (6, 400) meV range. Future
experiments and galaxy surveys, particularly the International Axion
Observatory (IAXO) and EUCLID, should have the capability to directly test this
scenario. In this paper, we will explore this mechanism in detail and give more
thorough computational details of certain key points.

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