Axino abundances in high-scale supersymmetry

TL;DR

This paper investigates the thermal production of axino dark matter in high-scale supersymmetry, highlighting how different axion models affect axino abundance and opening new parameter space for axino dark matter.

Contribution

It provides a detailed analysis of axino production mechanisms in high-scale SUSY, emphasizing the impact of model-dependent cross sections and entropy dilution effects.

Findings

Axino production cross section scales as T^4 in KSVZ model.

In DFSZ model, axino production cross section is temperature-independent.

New parameter space for axino dark matter is identified due to Higgsino interactions.

Abstract

We consider the thermal production of axino dark matter in high-scale supersymmetry where all the superpartners except the axino are heavier than the maximum and reheating temperatures. In this case, the axinos are produced dominantly in pairs from the scattering of SM particles in thermal plasma in the early Universe after inflation. We find that the thermal averaged scattering cross section for the axino pair production is given by $\langle\sigma v\rangle \propto T^4$ in Kim-Shifman-Vainstein-Zakharov (KSVZ) axion model, while it does not depend on the temperature in Dine-Fischler-Srednicki-Zhitnitski (DFSZ) axion model. As a result, the axinos produced during the early matter domination is diluted by the entropy production, so the axino abundance is determined mainly by the reheating temperature, unlike the case with gravitino dark matter. We show that the axino pair production in DFSZ model opens up new parameter space for axino dark matter, due to non-decoupled Higgsino interactions at tree level.