Degenerate Fermion Dark Matter from a Broken $U(1)_{rm B-L}$ Gauge Symmetry. (arXiv:2004.07863v1 [hep-ph])

Degenerate Fermion Dark Matter from a Broken $U(1)_{rm B-L}$ Gauge Symmetry. (arXiv:2004.07863v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Choi_G/0/1/0/all/0/1">Gongjun Choi</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Suzuki_M/0/1/0/all/0/1">Motoo Suzuki</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Yanagida_T/0/1/0/all/0/1">Tsutomu. T. Yanagida</a>

The extension of the Standard model by assuming $U(1)_{rm B-L}$ gauge
symmetry is very well-motivated since it naturally explains the presence of
heavy right-handed neutrinos required to account for the small active neutrino
masses via the seesaw mechanism and thermal leptogenesis. Traditionally, we
introduce three right handed neutrinos to cancel the $[U(1)_{rm B-L}]^3$
anomaly. However, it suffices to introduce two heavy right-handed neutrinos for
these purposes and therefore we can replace one right-handed neutrino by new
chiral fermions to cancel the $U(1)_{rm B-L}$ gauge anomaly. Then, one of the
chiral fermions can naturally play a role of a dark matter candidate. In this
paper, we demonstrate how this framework produces a dark matter candidate which
can address the so-called “core-cusp problem”. As one of the small scale
problems that $Lambda$CDM paradigm encounters, it may imply an important clue
for a nature of dark matter. One of resolutions among many is hypothesizing
that sub-keV fermion dark matter halos in dwarf spheroidal galaxies are in
(quasi) degenerate configuration. We show how the degenerate sub-keV fermion
dark matter candidate can be non-thermally originated in our model and thus can
be consistent with Lyman-$alpha$ forest observation. Thereby, the small
neutrino mass, baryon asymmetry, and the sub-keV dark matter become
consequences of the broken B-L gauge symmetry.

The extension of the Standard model by assuming $U(1)_{rm B-L}$ gauge
symmetry is very well-motivated since it naturally explains the presence of
heavy right-handed neutrinos required to account for the small active neutrino
masses via the seesaw mechanism and thermal leptogenesis. Traditionally, we
introduce three right handed neutrinos to cancel the $[U(1)_{rm B-L}]^3$
anomaly. However, it suffices to introduce two heavy right-handed neutrinos for
these purposes and therefore we can replace one right-handed neutrino by new
chiral fermions to cancel the $U(1)_{rm B-L}$ gauge anomaly. Then, one of the
chiral fermions can naturally play a role of a dark matter candidate. In this
paper, we demonstrate how this framework produces a dark matter candidate which
can address the so-called “core-cusp problem”. As one of the small scale
problems that $Lambda$CDM paradigm encounters, it may imply an important clue
for a nature of dark matter. One of resolutions among many is hypothesizing
that sub-keV fermion dark matter halos in dwarf spheroidal galaxies are in
(quasi) degenerate configuration. We show how the degenerate sub-keV fermion
dark matter candidate can be non-thermally originated in our model and thus can
be consistent with Lyman-$alpha$ forest observation. Thereby, the small
neutrino mass, baryon asymmetry, and the sub-keV dark matter become
consequences of the broken B-L gauge symmetry.

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