http://arxiv.org/abs/1612.05553
We study the impact of a modified expansion rate on the dark matter relic abundance in a class of scalar-tensor theories. The scalar-tensor theories we consider are motivated from string theory constructions, which have conformal as well as disformally coupled matter to the scalar. We investigate the effects of such a conformal coupling to the dark matter relic abundance for a wide range of initial conditions, masses and cross-sections. We find that exploiting all possible initial conditions, the annihilation cross-section required to satisfy the dark matter content can differ from the thermal average cross-section in the standard case. We also study the expansion rate in the disformal case and find that physically relevant solutions require a nontrivial relation between the conformal and disformal functions. We show an explicit example where the conformal function is set to be constant. For this case, the expansion rate modification is very mild, being almost indistinguishable from the standard cosmological evolution.
B. Dutta, E. Jimenez and I. Zavala
Wed, 21 Dec 16
28/67
Comments: 27 pages, 11 figures
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