Feebly Interacting Dark Matter Particle as the Inflaton

TL;DR

This paper proposes a unified scenario where a scalar field acts as both the inflaton and dark matter, produced via freeze-in, with specific parameter ranges fitting cosmological observations and distinguishable by future CMB measurements.

Contribution

It introduces a model-independent framework where a scalar field drives inflation, reheats the universe, and becomes dark matter, with minimal couplings and specific parameter constraints.

Findings

Scalar field can serve as inflaton and dark matter candidate.

Parameter ranges for coupling constants and mass are identified.

Model predictions are testable with future CMB observations.

Abstract

We present a scenario where a $Z_2$-symmetric scalar field $\phi$ first drives cosmic inflation, then reheats the Universe but remains out-of-equilibrium itself, and finally comprises the observed dark matter abundance, produced by particle decays \`{a} la freeze-in mechanism. We work model-independently without specifying the interactions of the scalar field besides its self-interaction coupling, $\lambda\phi^4$, non-minimal coupling to gravity, $\xi\phi^2R$, and coupling to another scalar field, $g\phi^2\sigma^2$. We find the scalar field $\phi$ serves both as the inflaton and a dark matter candidate if $10^{-9}\lesssim \lambda\lesssim g\lesssim 10^{-7}$ and $3 \rm{keV} \lesssim m_{\rm \phi}\lesssim 85 \rm{MeV}$ for $\xi=\mathcal{O}(1)$. Such a small value of the non-minimal coupling is also found to be of the right magnitude to produce the observed curvature perturbation amplitude within the scenario. We also discuss how the model may be distinguished from other inflationary models of the same type by the next generation CMB satellites.