Revisiting Cosmological Constraints on Supersymmetric SuperWIMPs

TL;DR

This paper reevaluates cosmological constraints on supersymmetric superWIMPs, such as gravitinos and axinos, using observations from Big Bang Nucleosynthesis, CMB, and small-scale structure to limit their properties and parameter space.

Contribution

It provides a comprehensive analysis of cosmological and collider constraints on superWIMPs, refining the allowed parameter space for gravitinos and axinos in supersymmetric models.

Findings

Cosmological observations strongly restrict superWIMP parameter space.

Late decays of parent particles impact BBN and CMB spectral features.

Small-scale structure data further limit superWIMP properties.

Abstract

SuperWIMPs are extremely weakly interacting massive particles that inherit their relic abundance from late decays of frozen-out parent particles. Within supersymmetric models, gravitinos and axinos represent two of the most well-motivated superWIMPs. In this paper we revisit constraints on these scenarios from a variety of cosmological observations that probe their production mechanisms as well as the superWIMP kinematic properties in the early Universe. We consider in particular observables of Big Bang Nucleosynthesis and the Cosmic Microwave Background (spectral distortion and anisotropies), which limit the fractional energy injection from the late decays, as well as warm and mixed dark matter constraints derived from the Lyman-$\alpha$ forest and other small-scale structure observables. We discuss complementary constraints from collider experiments, and argue that cosmological considerations rule out a significant part of the gravitino and the axino superWIMP parameter space.