Nicolas Fernandez (UIUC)
Title: Freeze-in, glaciation, and UV sensitivity from light mediators
Dark matter (DM) freeze-in through a light mediator is an appealing model with excellent detection prospects at current and future experiments. Light mediator freeze-in is UV-insensitive insofar as most DM is produced at late times, and thus the DM abundance does not depend on the unknown early evolution of our universe. However the final DM yield retains a dependency on the initial conditions for the DM abundance, which is usually assumed to be exactly zero. We point out that in models with light mediators, the final DM yield will also depend on the initial conditions assumed for the light mediator population. We describe a class of scenarios we call “glaciation” where DM freezing in from the SM encounters a pre-existing thermal bath of mediators, and study the dependence of the final DM yield on the initial temperature of this dark radiation bath. We quantify the dependence of the DM yield on the initial dark temperature and find that it can be sizeable in regions near the traditional (zero initial abundance) freeze-in curve. We generalize the freeze-in curve to a glaciation band, which can extend as much as an order of magnitude below the traditional freeze-in direct detection target, and point out that the DM phase space distribution as well as the yield can be strongly dependent on initial conditions.
Trey Jensen (NYU)
Title: The impact on cosmological observables from dark matter's inhomogeneous energy injection
The effect of homogeneous energy injection on cosmology is the basis of many constraints imposed on exotic dark matter candidates. One aspect that has not been inspected in detail is how an inhomogeneous energy injection uniquely impacts cosmological observables. In this talk, I will discuss our developed radiation transport simulation that characterizes the spatial energy deposition of ~MeV photons in a cosmological plasma. Specifically, we apply this work on accreting primordial black holes as a dark matter candidate. Because inhomogeneous energy injection results in an inhomogeneous recombination history of the primordial plasma, there will be a unique non-Gaussian signature in observables such as the cosmic microwave background radiation anisotropy. The null results of such signatures could be used as powerful constraining tools for not only accreting PBHs, but other exotic DM candidates.