Post-Inflationary Dark Matter Bremsstrahlung

TL;DR

This paper investigates how dark matter can be produced during reheating via bremsstrahlung from inflaton decay products, especially at low reheating temperatures, providing a new mechanism for UV freeze-in.

Contribution

It introduces a novel calculation of dark matter production through bremsstrahlung during reheating, emphasizing its dominance at low reheating temperatures and specific UV scales.

Findings

Bremsstrahlung dominates dark matter production for $T_{RH} \\lesssim 10^{10}$ GeV.

The process can generate the correct dark matter abundance at a UV scale of about $10^{16}$ GeV.

Numerical examples include gravitational and vector portal interactions.

Abstract

Dark matter may only interact with the visible sector efficiently at energy scales above the inflaton mass, such as the Planck scale or the grand unification scale. In such a scenario, the dark matter is mainly produced out of equilibrium during the period of reheating, often referred to as UV freeze-in. We evaluate the abundance of the dark matter generated from bremsstrahlung off the inflaton decay products assuming no direct coupling between the inflaton and the dark matter. This process generally dominates the production of dark matter for low reheating temperatures where the production through the annihilations of particle in the thermal plasma becomes inefficient. We find that the bremsstrahlung process dominates for reheating temperatures $T_{\mathrm{RH}} \lesssim 10^{10}$ GeV, and produces the requisite density of dark matter for a UV scale $\simeq 10^{16}$ GeV. As examples, we calculate numerically the yield of the dark matter bremsstrahlung through gravitation and dimension-6 vector portal effective interactions.