Axinos in Cosmology and at Colliders

TL;DR

This paper investigates the role of axinos as dark matter candidates, analyzing their decay processes, cosmological constraints, and collider signatures, especially in scenarios with long-lived charged sleptons.

Contribution

It provides the first complete calculation of decay rates for the NLSP in axino scenarios, including two-loop contributions, and explores collider and cosmological implications.

Findings

Long-lived charged sleptons can decay via suppressed channels involving axinos.

Cosmological constraints restrict the parameter space for axino and gravitino masses.

Collider signatures include long-lived charged particles detectable at colliders.

Abstract

The axino, the fermionic superpartner of the axion, is a well-motivated candidate for cold dark matter if it is the lightest supersymmetric particle. Since the axino couples very weakly to the matter multiplets, the next-to-lightest supersymmetric particle (NLSP) has a long lifetime, which has important consequences for both cosmology and collider phenomenology. Assuming that a charged slepton is the NLSP, we calculate the complete leading one- and two-loop contributions to its decay. We analyze in detail constraints on the parameters space from cosmology and discuss how this scenario can be probed at colliders. Scenarios in which both the axino and the gravitino are lighter than the long-lived charged slepton are also explored with particular emphasis on cosmological constraints and collider phenomenology.