Warm dark matter from freeze-in at stronger coupling

Abstract

We study warm Higgs portal dark matter (DM) in the framework of freeze-in at stronger coupling. This scenario assumes that the Standard Model thermal bath temperature has always been relatively low, which suppresses dark matter production. As a result, a significant DM-Higgs coupling is allowed, enabling warm dark matter detection via Higgs decay at colliders. We find that the Lyman-α bound on the DM mass is particularly strong, excluding masses below 50-100 keV, depending on further details. The shape of the DM momentum distribution is highly non-thermal, with low momenta being effectively cut off, and not captured by the common αβγ-parametrization.

Figures (7)

• Figure 1: Dark matter production via pion and muon annihilation.
• Figure 2: Temperature of the Standard Model sector in the postinflationary epoch (on a logarithmic scale), with reheating at $a\sim a_R$. The different scenarios represent: (1) direct SM particle production through inflaton decay, $n-m>0$, (2) SM sector production via a cascade decay, $n-m=0$, (3) SM sector production via a longer cascade decay, $n-m<0$.
• Figure 3: Production of one hard and one soft DM particle via a relativistic pion collision. Corrections of order $m_\pi^2/p_0$ to the pion momenta are neglected.
• Figure 4: Comoving momentum distribution function of DM produced via pion annihilation, with $T_R=50\;$MeV and assuming instant-like reheating. For convenience, $f(q)$ is normalized to 1 at the maximum.
• Figure 5: Parameter space of the Higgs portal DM model at low masses. Along the colored lines, the observed DM abundance is reproduced, for a given $T_R$ (in MeV). The shaded areas are excluded by the LHC and Lyman-$\alpha$ constraints, while the dashed lines show the prospects of DM detection via invisible Higgs decay.