Strongly-Interacting Ultralight Millicharged Particles. (arXiv:2011.06589v2 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Alexander_S/0/1/0/all/0/1">Stephon Alexander</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McDonough_E/0/1/0/all/0/1">Evan McDonough</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spergel_D/0/1/0/all/0/1">David N. Spergel</a>
We consider the implications of an ultra-light fermionic dark matter
candidate that carries baryon number. This naturally arises if dark matter has
a small charge under standard model baryon number whilst having an asymmetry
equal and opposite to that in the visible universe. A prototypical model is a
theory of dark baryons of a non-Abelian gauge group, i.e., a dark Quantum
Chromo-Dynamics (QCD). For sub-eV dark baryon masses, the inner region of dark
matter halos is naturally at ‘nuclear density’, allowing for the formation of
exotic states of matter, akin to neutron stars. The Tremaine-Gunn lower bound
on the mass of fermionic dark matter, i.e., the dark baryons, is violated by
the strong short-range self-interactions, cooling via emission of light dark
pions, and the Cooper pairing of dark quarks that occurs at densities that are
high relative to the (ultra-low) dark QCD scale. We develop the astrophysics of
these STrongly-interacting Ultra-light Millicharged Particles (STUMPs)
utilizing the equation of state of dense quark matter, and find halo cores
consistent with observations of dwarf galaxies. These cores are prevented from
core-collapse by pressure of the ‘neutron star’, which suggests ultra-light
dark QCD as a resolution to core-cusp problem of collisionless cold dark
matter. The model is distinguished from ultra-light bosonic dark matter through
direct detection and collider signatures, as well as by phenomena associated
with superconductivity, such as Andreev reflection and superconducting
vortices.
We consider the implications of an ultra-light fermionic dark matter
candidate that carries baryon number. This naturally arises if dark matter has
a small charge under standard model baryon number whilst having an asymmetry
equal and opposite to that in the visible universe. A prototypical model is a
theory of dark baryons of a non-Abelian gauge group, i.e., a dark Quantum
Chromo-Dynamics (QCD). For sub-eV dark baryon masses, the inner region of dark
matter halos is naturally at ‘nuclear density’, allowing for the formation of
exotic states of matter, akin to neutron stars. The Tremaine-Gunn lower bound
on the mass of fermionic dark matter, i.e., the dark baryons, is violated by
the strong short-range self-interactions, cooling via emission of light dark
pions, and the Cooper pairing of dark quarks that occurs at densities that are
high relative to the (ultra-low) dark QCD scale. We develop the astrophysics of
these STrongly-interacting Ultra-light Millicharged Particles (STUMPs)
utilizing the equation of state of dense quark matter, and find halo cores
consistent with observations of dwarf galaxies. These cores are prevented from
core-collapse by pressure of the ‘neutron star’, which suggests ultra-light
dark QCD as a resolution to core-cusp problem of collisionless cold dark
matter. The model is distinguished from ultra-light bosonic dark matter through
direct detection and collider signatures, as well as by phenomena associated
with superconductivity, such as Andreev reflection and superconducting
vortices.
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