Mirage in the Sky: Non-thermal Dark Matter, Gravitino Problem, and Cosmic Ray Anomalies

TL;DR

This paper proposes a non-thermal dark matter production mechanism involving late-time reheating from heavy moduli or gravitino decay, which explains cosmic ray anomalies and addresses cosmological problems.

Contribution

It introduces a novel non-thermal relic density scenario in string-inspired models that fits cosmic ray data and solves the gravitino and moduli problems.

Findings

Reheating from moduli or gravitino decay can produce the correct dark matter relic density.

The scenario explains cosmic ray anomalies with large dark matter annihilation cross-sections.

Distinguishable signatures between thermal and non-thermal dark matter scenarios in direct detection experiments.

Abstract

Recent anomalies in cosmic rays could be due to dark matter annihilation in our galaxy. In order to get the required large cross-section to explain the data while still obtaining the right relic density, we rely on a non standard thermal history between dark matter freeze-out and Big-Bang Nucleosynthesis (BBN). We show that through a reheating phase from the decay of a heavy moduli or even the gravitino, we can produce the right relic density of dark matter if its self-annihilation cross-section is large enough. In addition to fitting the recent data, this scenario solves the cosmological moduli and gravitino problems. We illustrate this mechanism with a specific example in the context of U(1)_{B-L} extended MSSM where supersymmetry is broken via mirage mediation. These string motivated models naturally contain heavy moduli decaying to the gravitino, whose subsequent decay to the LSP can reheat the universe at a low temperature. The right-handed sneutrino and the B-L gaugino can both be viable dark matter candidates with large cross-section. They are leptophilic because of B-L charges. We also show that it is possible to distinguish the non-thermal from the thermal scenario (using Sommerfeld enhancement) in direct detection experiments for certain regions of parameter space.