Dark Radiation from Modulated Reheating

TL;DR

This paper proposes that modulated reheating naturally produces light moduli that can account for dark radiation, aligning with recent cosmological observations and potentially contributing to dark matter.

Contribution

It demonstrates that the modulated reheating mechanism can generate dark radiation from light moduli, providing a new explanation consistent with observational data.

Findings

Light moduli are produced during inflaton decay and can serve as dark radiation.

The power spectrum from modulated reheating fits observations better with extra radiation.

The model allows the modulus to potentially become the dominant dark matter component.

Abstract

We show that the modulated reheating mechanism can naturally account for dark radiation, whose existence is hinted by recent observations of the cosmic microwave background radiation and the primordial Helium abundance. In this mechanism, the inflaton decay rate depends on a light modulus which acquires almost scale-invariant quantum fluctuations during inflation. We find that the light modulus is generically produced by the inflaton decay and therefore a prime candidate for the dark radiation. Interestingly, an almost scale-invariant power spectrum predicted in the modulated reheating mechanism gives a better fit to the observation in the presence of the extra radiation. We discuss the production mechanism of the light modulus in detail taking account of its associated isocurvature fluctuations. We also consider a case where the modulus becomes the dominant component of dark matter.