Dark radiation and small-scale structure problems with decaying particles

TL;DR

This paper proposes a supersymmetric axion model where late decays produce warm dark matter and dark radiation, addressing tensions in small-scale structure and effective neutrino number.

Contribution

It introduces a novel scenario with late decays of heavy particles generating both dark matter and dark radiation, resolving existing cosmological tensions.

Findings

Identifies parameter space satisfying cosmological constraints

Dark matter is warm, alleviating small-scale structure issues

Dark radiation from axion production matches observations

Abstract

Although the standard {\Lambda}CDM model describes the cosmic microwave background radiation and the large scale structure of the Universe with great success, it has some tensions with observations in the effective number of neutrino species (dark radiation) and the number of small scale structures (overabundance problem). Here we propose a scenario which can relax these tensions by producing both dark matter and dark radiation by late decays of heavy particle. Thanks to the generation mechanism, dark matters are rather warm so that the small-scale structure problem is resolved. This scenario can be naturally realized in supersymmetric axion model, in which axions produced by saxion decays provide dark radiation, while axinos from saxion decays form warm dark matter. We identify a parameter region of supersymmetric axion model satisfying all known cosmological constraints.