Bound state effects on dark matter coannihilation: pushing the boundaries of conversion-driven freeze-out. (arXiv:2112.01499v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Garny_M/0/1/0/all/0/1">Mathias Garny</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Heisig_J/0/1/0/all/0/1">Jan Heisig</a>
Bound state formation can have a large impact on the dynamics of dark matter
freeze-out in the early Universe, in particular for colored coannihilators. We
present a general formalism to include an arbitrary number of excited bound
states in terms of an effective annihilation cross section, taking bound state
formation, decay as well as transitions into account, and derive analytic
approximations in the limiting cases of no or efficient transitions.
Furthermore, we provide explicit expressions for radiative bound state
formation rates for states with arbitrary principal and angular quantum numbers
$n,ell$ for a mediator in the fundamental representation of $SU(3)_c$, as well
as electromagnetic transition rates among them in the Coulomb approximation. We
then assess the impact of bound states within a model with Majorana dark matter
and a colored scalar $t$-channel mediator. We consider the regime of
coannihilation as well as conversion-driven freeze-out (or coscattering), where
the relic abundance is set by the freeze-out of conversion processes. We find
that the region in parameter space where the latter occurs is considerably
enhanced into the multi-TeV regime. For conversion-driven freeze-out dark
matter is very weakly coupled, evading direct and indirect detection
constraints, but leading to prominent signatures of long-lived particles that
provide great prospects to be probed by dedicated searches at the upcoming LHC
runs.
Bound state formation can have a large impact on the dynamics of dark matter
freeze-out in the early Universe, in particular for colored coannihilators. We
present a general formalism to include an arbitrary number of excited bound
states in terms of an effective annihilation cross section, taking bound state
formation, decay as well as transitions into account, and derive analytic
approximations in the limiting cases of no or efficient transitions.
Furthermore, we provide explicit expressions for radiative bound state
formation rates for states with arbitrary principal and angular quantum numbers
$n,ell$ for a mediator in the fundamental representation of $SU(3)_c$, as well
as electromagnetic transition rates among them in the Coulomb approximation. We
then assess the impact of bound states within a model with Majorana dark matter
and a colored scalar $t$-channel mediator. We consider the regime of
coannihilation as well as conversion-driven freeze-out (or coscattering), where
the relic abundance is set by the freeze-out of conversion processes. We find
that the region in parameter space where the latter occurs is considerably
enhanced into the multi-TeV regime. For conversion-driven freeze-out dark
matter is very weakly coupled, evading direct and indirect detection
constraints, but leading to prominent signatures of long-lived particles that
provide great prospects to be probed by dedicated searches at the upcoming LHC
runs.
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