Speaker
Description
In this talk, we discuss new freeze-in dark matter (DM) benchmarks for the next generation of direct detection experiments. We focus on the MeV-scale fermionic dark matter coupled to the Standard Model via a new vector mediator. First, we investigate the minimal kinetic mixing dark photon of a secluded $U(1)_{D}$. Then, we study the gauge bosons of the anomaly-free $U(1)_{L_{i}-L_{j}}$ with $i,j= e,\mu,\tau$ and $U(1)_{B-L}$, exploring the impact of low reheating scenarios on the DM production rates. In the ultralight dark photon scenario, DAMIC-M and PandaX-4T bounds can be avoided if the DM fermion constitutes less than 40\% of the total cold DM. In this regard, future direct detection experiments can be sensitive to a fraction below 1\% for masses below 1 MeV. For a massive dark photon, there are allowed regions of the parameter space with masses in the range 50 MeV $\lesssim m_{DM} \lesssim $ 500 MeV, within reach of direct detection experiments through nuclear recoils if freeze-in occurred at a low reheating temperatures. In the case of $U(1)_{L_{i}-L_{j}}$ and $U(1)_{B-L}$, freeze-in at low reheating temperatures can reproduce the observed relic abundance in large parts of the parameter space, up to gauge couplings of $g_{X}\sim10^{-2}$ for MeV DM. Direct detection experiments will be sensitive to considerable parts of this parameter space in nuclear recoils for 50 MeV $\lesssim m_{DM} \lesssim $ 500 MeV. In addition, we find beyond Standard Model (BSM) signals not only in the dark matter (DM) sector, but also in neutrino physics. Additionally, the enhanced signal from solar neutrino coherent scattering
is observable in these scenarios, which can serve as a further handle to identify the underlying particle physics model.