Cold Dark Matter in non-Standard Cosmologies, PAMELA, ATIC and Fermi LAT

TL;DR

This paper explores how non-standard cosmological models can enhance WIMP relic density, allowing compatibility with cosmic ray data from PAMELA, ATIC, and Fermi LAT, especially for WIMPs annihilating to muons.

Contribution

It demonstrates that low reheating or quintessence-dominated scenarios can increase WIMP relic density, fitting cosmic ray data with larger annihilation cross sections.

Findings

Enhanced WIMP relic density in non-standard cosmologies.

Good fit to PAMELA and Fermi-LAT data with muon-dominant annihilation.

Transition temperature to standard cosmology below 0.7 GeV.

Abstract

We consider two non-standard cosmological scenaria according to which the universe is reheated to a low reheating temperature after the late decay of a scalar field or is dominated by the kinetic energy of a quintessence field in the context of a tracking quintessential model. In both cases, we calculate the relic density of the \emph{Weakly Interacting Massive Particles} (WIMPs) and show that it can be enhanced with respect to its value in the standard cosmology. By adjusting the parameters of the low reheating or the quintessential scenario, the cold dark matter abundance in the universe can become compatible with large values for the annihilation cross section times the velocity of the WIMPs. Using these values and assuming that the WIMPs annihilate predominantly to $e^+e^-$, $\mu^+\mu^-$ or $\tau^+\tau^-$, we calculate the induced fluxes of $e^\pm$ cosmic rays and fit the current data of PAMELA and ATIC or Fermi LAT. We achieve rather good fits especially to PAMELA and Fermi-LAT data in conjunction with a marginal fulfillment of the restriction arising from cosmic microwave background, provided that the WIMPs annihilate predominantly to $\mu^+\mu^-$. In both non-standard scenaria the required transition temperature to the conventional radiation dominated era turns out to be lower than about $0.7 \GeV$. In the case of the low reheating, an appreciable non-thermal contribution to the WIMP relic density is also necessitated.