A Non-thermal WIMP Miracle

TL;DR

The paper addresses the tension between the Thermal WIMP Miracle and UV completions featuring light, gravitationally coupled moduli that can dominate the early universe. It analyzes a generic supergravity framework where moduli decay reheats the Universe before BBN and non-thermally generates WIMP dark matter, deriving a relic-density relation that scales as $\Omega_\chi h^2 \sim 0.1 (m_\chi/100\;GeV) (100\;TeV/m_\phi)^{3/2} (\sigma_0/\langle \sigma v \rangle)$ and matches observation for $m_\phi$ in the 10-100 TeV range. The result requires larger $\langle \sigma v \rangle$ than the thermal case and predicts a characteristic spectrum with heavy scalars and lighter gauginos, compatible with AMSB-like scenarios such as G2-MSSM. This non-thermal WIMP Miracle provides a UV-complete, string-motivated alternative to the thermal relic, with potential implications for indirect detection and early-universe cosmology, including baryogenesis.

Abstract

Light scalar fields with only gravitational strength couplings are typically present in UV complete theories of physics beyond the Standard Model. In the early universe it is natural for these fields to dominate the energy density, and their subsequent decay, if prior to BBN, will typically yield some dark matter particles in their decay products. In this paper we make the observation that a Non-thermal WIMP `Miracle' may result: that is, in the simplest solution to the cosmological moduli problem, non-thermally produced WIMPs can naturally account for the observed dark matter relic density. Such a solution may be generic in string theory compactifications.