Making dark matter out of light: freeze-in from plasma effects. (arXiv:1902.08623v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Dvorkin_C/0/1/0/all/0/1">Cora Dvorkin</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Lin_T/0/1/0/all/0/1">Tongyan Lin</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Schutz_K/0/1/0/all/0/1">Katelin Schutz</a>
Dark matter (DM) could couple to particles in the Standard Model (SM) through
a light vector mediator. In the limit of small coupling, this portal could be
responsible for producing the observed DM abundance through a mechanism known
as freeze-in. Furthermore, the requisite DM-SM couplings provide a concrete
benchmark for direct and indirect searches for DM. In this paper, we present
updated calculations of the relic abundance for DM produced by freeze-in
through a light vector mediator. We identify an additional production channel:
the decay of photons that acquire an in-medium plasma mass. These plasmon
decays are a dominant channel for DM production for sub-MeV DM masses, and
including this channel leads to a significant reduction in the predicted signal
strength for DM searches. Accounting for production from both plasmon decays
and annihilations of SM fermions, the DM acquires a highly non-thermal phase
space distribution which impacts the cosmology at later times; these
cosmological effects will be explored in a companion paper.
Dark matter (DM) could couple to particles in the Standard Model (SM) through
a light vector mediator. In the limit of small coupling, this portal could be
responsible for producing the observed DM abundance through a mechanism known
as freeze-in. Furthermore, the requisite DM-SM couplings provide a concrete
benchmark for direct and indirect searches for DM. In this paper, we present
updated calculations of the relic abundance for DM produced by freeze-in
through a light vector mediator. We identify an additional production channel:
the decay of photons that acquire an in-medium plasma mass. These plasmon
decays are a dominant channel for DM production for sub-MeV DM masses, and
including this channel leads to a significant reduction in the predicted signal
strength for DM searches. Accounting for production from both plasmon decays
and annihilations of SM fermions, the DM acquires a highly non-thermal phase
space distribution which impacts the cosmology at later times; these
cosmological effects will be explored in a companion paper.
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