Abstract
Thermal freeze-out or freeze-in during a period of early matter domination can give rise to the correct dark matter abundance for $\langle \sigma_{\rm ann} v \rangle_{\rm f} < 3 \times 10^{-26}$ cm$^3$ s$^{-1}$. In the standard scenario, a single field that behaves like matter drives the early matter dominated era. However, in realistic models, this epoch may involve more than one field. In this paper, we study the effect of such a modification on the production of dark matter during early matter domination. We show that even a subdominant second field that decays much faster than the dominant one can considerably enhance the temperature of the universe during an early matter-dominated phase. This in turn affects dark matter production via freeze-out/in and opens up the allowed parameter space toward significantly larger dark matter masses. As a result, one can comfortably obtain the correct relic abundance for PeV-scale dark matter for reheating temperatures at or below 10 GeV.
Highlights
There are various lines of evidence that most of the matter in the Universe is dark [1]
We have shown how a second field can enhance the temperature of the Universe and thereby affect dark matter (DM) production during early matter domination (EMD)
A natural possibility that can arise in string constructions is that φ and φ are both modulus fields
Summary
There are various lines of evidence that most of the matter in the Universe is dark [1]. Thermal freezeout in a radiation-dominated (RD) universe can yield the correct DM abundance if the annihilation rate takes the nominal value hσannvif 1⁄4 3 × 10−26 cm s−1 (called “WIMP miracle”). This scenario has come under pressure by recent experiments. Fermi-LAT’s results from observations of dwarf spheroidal galaxies [2] and newly discovered Milky Way satellites [3] have placed upper bounds on hσannvif that are below the nominal value for certain final states Based on these results, a recent analysis [4] has ruled out thermal DM with a mass below 20 GeV in a model-independent way (unless there is P-wave annihilation or coannihilation). Some of the details of our calculations are included in the Appendixes
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