Joint Cosmic Microwave Background and Big Bang Nucleosynthesis Constraints on Light Dark Sectors with Dark Radiation.

Dark sectors provide a compelling theoretical framework for thermally producing sub-GeV dark matter, and motivate an expansive new accelerator and direct-detection experimental program. We demonstrate the power of constraining such dark sectors using the measured effective number of neutrino species, N_{eff}, from the cosmic microwave background (CMB) and primordial elemental abundances from big bang nucleosynthesis. As a concrete example, we consider a dark matter particle of arbitrary spin that interacts with the standard model via a massive dark photon, accounting for an arbitrary number of light degrees of freedom in the dark sector.

Erratum: Dark Matter from Exponential Growth [Phys. Rev. Lett. 127, 191802 (2021)].

This corrects the article DOI: 10.1103/PhysRevLett.127.

Dark Matter from Exponential Growth.

We propose a novel mechanism for the production of dark matter (DM) from a thermal bath based on the idea that DM particles χ can transform heat bath particles ψ: χψ→χχ. For a small initial abundance of χ, this leads to an exponential growth of the DM number density in close analogy to other familiar exponential growth processes in nature. We demonstrate that this mechanism complements freeze-in and freeze-out production in a generic way, opening new parameter space to explain the observed DM abundance, and we discuss observational prospects for such scenarios.

Edges and Endpoints in 21-cm Observations from Resonant Photon Production.

We introduce a novel class of signatures-spectral edges and end points-in 21-cm measurements resulting from interactions between the standard and dark sectors. Within the context of a kinetically mixed dark photon, we demonstrate how resonant dark photon-to-photon conversions can imprint distinctive spectral features in the observed 21-cm brightness temperature, with implications for current, upcoming, and proposed experiments targeting the cosmic dawn and the dark ages. These signatures open up a qualitatively new way to look for physics beyond the Standard Model using 21-cm observations.

Heavy Thermal Dark Matter from a New Collision Mechanism.

We propose a new thermal freeze-out mechanism that results in dark matter masses exceeding the unitarity bound by many orders of magnitude, without violating perturbative unitarity or modifying the standard cosmology. The process determining the relic abundance is χζ^{†}→ζζ, where χ is the dark matter candidate. For m_{ζ} View Article and Find Full Text PDF