Non-thermal WIMP Production from Higher Order Moduli Decay

TL;DR

This paper investigates non-thermal WIMP production from moduli decay, focusing on higher order decay processes and their impact on dark matter relic abundance within supersymmetric models.

Contribution

It calculates three- and four-body decay branching ratios of moduli into WIMPs and applies these to MSSM, revealing new constraints on sparticle masses and decay couplings.

Findings

Higher order decay processes can significantly affect WIMP relic density calculations.

In MSSM, satisfying the branching ratio bounds requires sparticle masses near half the modulus mass.

Appropriate coupling choices can reconcile decay bounds with simplified models.

Abstract

In a non-standard cosmological scenario, heavy, long-lived particles, which we call moduli, dominate the energy density prior to Big Bang Nucleosynthesis. Weakly Interacting Massive Particles (WIMPs) may be produced non-thermally from moduli decays. The final relic abundance then depends on additional parameters such as the branching ratio of moduli to WIMPs and the modulus mass. This is of interest for WIMP candidates, such as a bino-like neutralino, where thermal production in standard cosmology leads to an overdensity. Previous works have shown that the correct dark matter (DM) relic density can then still be obtained if the moduli, with mass less than $10^{7}$ GeV, decay to WIMPs with a branching ratio of less than $10^{-4}$. This upper bound could easily be violated once higher order corrections, involving final states with more than two particles, are included. We compute the branching ratios of three- and four-body decays of a modulus into final states involving two DM particles for general couplings. We then apply these expressions to sparticle production within the Minimal Supersymmetric Standard Model (MSSM) with neutralino DM. We find that this upper bound on the branching ratio can be satisfied in simplified models through an appropriate choice of as yet undetermined couplings. However, in the MSSM, it requires sparticle masses to be very close to half the modulus mass, in contrast to the idea of weak-scale supersymmetry.