Dark Matter Production in Weyl $R^2$ Inflation

TL;DR

This paper explores how a Weyl $R^2$ gravity model can simultaneously explain inflation and dark matter production, identifying parameter ranges for viable dark matter candidates through non-perturbative and perturbative mechanisms.

Contribution

It introduces a unified framework using Weyl $R^2$ gravity to account for both inflation and dark matter, analyzing production mechanisms and parameter spaces.

Findings

Dark matter can be produced abundantly with mass > $10^{13}$ GeV for high reheating temperatures.

Small dark matter masses around $3 imes 10^{-13}$ GeV are possible at higher reheating temperatures.

Freeze-in production allows dark matter masses up to $4 imes 10^{16}$ GeV with higher reheating temperatures.

Abstract

Dark matter and inflation are two key elements to understand the origin of cosmic structures in modern cosmology, and yet their exact physical models remain largely uncertain. The Weyl scaling invariant theory of gravity may provide a feasible scheme to solve these two puzzles jointly, which contains a massive gauge boson playing the role of dark matter candidate, and allows the quadratic scalar curvature term, namely $R^2$, to realize a viable inflationary mechanism in agreement with current observations. We ponder on the production of dark matters in the Weyl $R^2$ model, including the contribution from the non-perturbative production due to the quantum fluctuations from inflationary vacuum and perturbative ones from scattering. We demonstrate that there are generally three parameter ranges for viable dark matter production: (1) If the reheating temperature is larger than $10^3~\mathrm{GeV}$, the Weyl gauge boson as dark matter can be produced abundantly with mass larger than the inflation scale $\sim 10^{13}~\mathrm{GeV}$. (2) Small mass region with $3\times10^{-13}~\mathrm{GeV}$ for a higher reheating temperature. (3) Annihilation channel becomes important in the case of higher reheating temperature, which enables the Weyl gauge boson with mass up to $4\times10^{16}~\mathrm{GeV}$ to be produced through freeze-in.