Dark radiation from the axino solution of the gravitino problem

TL;DR

This paper explores how a light axino solving the gravitino problem can naturally produce dark radiation, impose bounds on reheating temperature, and relate to dark matter and leptogenesis, with potential experimental support from the LHC.

Contribution

It introduces a scenario where axinos resolve the gravitino problem and generate dark radiation, providing new bounds on reheating temperature and linking to dark matter and leptogenesis.

Findings

Reheating temperature T_R < 10^{11} GeV is established.

Dark radiation increase is compatible with cosmic microwave background observations.

Axion and axino can account for observed dark matter.

Abstract

Current observations of the cosmic microwave background could confirm an increase in the radiation energy density after primordial nucleosynthesis but before photon decoupling. We show that, if the gravitino problem is solved by a light axino, dark (decoupled) radiation emerges naturally in this period leading to a new upper bound on the reheating temperature T_R < 10^{11} GeV. In turn, successful thermal leptogenesis might predict such an increase. The Large Hadron Collider could endorse this opportunity. At the same time, axion and axino can naturally form the observed dark matter.