Velocity-dependent self-interacting dark matter from thermal freeze-out and tests in direct detections. (arXiv:1910.05633v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Jia_L/0/1/0/all/0/1">Lian-Bao Jia</a>
A small fraction of millicharged dark matter (DM) is considered in the
literature to give an interpretation about the enhanced 21-cm absorption at the
cosmic dawn, while the main component of DM is still unclear. Here we focus on
the case that the main component is self-interacting dark matter (SIDM),
motivated by the small scale problems. For self interactions of SIDM being
compatible from dwarf to cluster scales, Sommerfeld enhanced velocity-dependent
self interactions mediated by a light scalar $phi$ is considered. To fermionic
SIDM $Psi$, the main annihilation mode $Psi bar{Psi} to phi phi$ is a $p
-$wave process, which could evade constraints from CMB and indirect detections.
For thermal freeze-out type SIDM, the thermal equilibrium between SIDM and the
standard model (SM) particles in the early universe via the transition of SIDM
$rightleftarrows phi rightleftarrows$ SM sets a lower bound on couplings of
$phi$ to SM particles, which has been excluded by DM direct detections, and
here we consider SIDM in the thermal equilibrium with millicharged DM. For
$m_phi >$ twice millicharged DM mass, $phi$’s lifetime could be much smaller
than 1 second, avoiding excess energy injection to the big bang
nucleosynthesis. Thus, the $phi -$SM particle couplings could be very tiny and
evade DM direct detections. The momentum transfer in SIDM-target nucleus
scattering may be comparable with $m_phi$ in direct detections, and the
picture of WIMP-nucleus scattering with contact interactions fails for
SIDM-nucleus scattering with a light mediator. A method is explored in this
paper, with which a WIMP search result can be converted into the hunt for SIDM
in direct detections.
A small fraction of millicharged dark matter (DM) is considered in the
literature to give an interpretation about the enhanced 21-cm absorption at the
cosmic dawn, while the main component of DM is still unclear. Here we focus on
the case that the main component is self-interacting dark matter (SIDM),
motivated by the small scale problems. For self interactions of SIDM being
compatible from dwarf to cluster scales, Sommerfeld enhanced velocity-dependent
self interactions mediated by a light scalar $phi$ is considered. To fermionic
SIDM $Psi$, the main annihilation mode $Psi bar{Psi} to phi phi$ is a $p
-$wave process, which could evade constraints from CMB and indirect detections.
For thermal freeze-out type SIDM, the thermal equilibrium between SIDM and the
standard model (SM) particles in the early universe via the transition of SIDM
$rightleftarrows phi rightleftarrows$ SM sets a lower bound on couplings of
$phi$ to SM particles, which has been excluded by DM direct detections, and
here we consider SIDM in the thermal equilibrium with millicharged DM. For
$m_phi >$ twice millicharged DM mass, $phi$’s lifetime could be much smaller
than 1 second, avoiding excess energy injection to the big bang
nucleosynthesis. Thus, the $phi -$SM particle couplings could be very tiny and
evade DM direct detections. The momentum transfer in SIDM-target nucleus
scattering may be comparable with $m_phi$ in direct detections, and the
picture of WIMP-nucleus scattering with contact interactions fails for
SIDM-nucleus scattering with a light mediator. A method is explored in this
paper, with which a WIMP search result can be converted into the hunt for SIDM
in direct detections.
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