Light dark photon and fermionic dark radiation for the Hubble constant and the structure formation

摘要

Motivated by the tensions in the Hubble constant H-0 and the structure growth sigma(8) between Planckresults and other low redshift measurements, we discuss some cosmological effects of a dark sector model in which dark matter (DM) interacts with fermionic dark radiation (DR) through a light gauge boson (dark photon). Such kind of models are very generic in particle physics with a dark sector with dark gauge symmetries. The effective number of neutrinos is increased by delta N-eff similar to 0.5 due to light dark photon and fermionic DR, thereby resolving the conflicts in H-0. The elastic scattering between DM and DR induces suppression for DM's density perturbation, but without acoustic oscillations. For weakly-interacting DM around 100GeV, the new gauge coupling should be similar to 10(-4) to have sizable effect on matter power spectrum in order to relax the tension in s8. (C) 2016 The Author(s). Published by Elsevier B.V.