Non-thermal WIMP Production from Higher Order Moduli Decay

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.