Free scalar dark matter candidates in R^2-inflation: the light, the heavy and the superheavy

TL;DR

This paper explores various scalar dark matter candidates produced during R^2-inflation, identifying conditions under which they can serve as viable warm, cold, or supercold dark matter based on their mass and coupling.

Contribution

It investigates the production of free scalar and fermion dark matter during R^2-inflation, highlighting the roles of non-minimal coupling and superheavy masses in viable dark matter scenarios.

Findings

Scalar dark matter with mass >0.8 MeV can be warm or cold.

Superheavy scalar and fermion dark matter with mass ~10^16 GeV are viable.

Production mechanisms depend on non-minimal coupling and adiabaticity violation.

Abstract

Gravity takes care of both inflation and subsequent reheating in Starobinsky's R^2-model. The latter is due to inflaton gravitation decays dominated by scalar particle production. It is tempting to suggest that dark matter particles are also produced in this process. Since free scalars being too hot cannot serve as viable dark matter (Phys.Lett.B700:157-162,2011), we further study the issue considering two options: scalars with non-minimal coupling to gravity and superheavy scalars generated at inflationary stage. We found that the first option allows for viable warm or cold dark matter if scalar mass exceeds 0.8 MeV. The second option implies supercold dark matter with particle mass 10^16 GeV, which production is saturated at the end of inflation when inflaton-dependent scalar mass rapidly changes and violates adiabaticity. Similar result holds for superheavy fermion dark matter.