Implications of a Late-Time Interaction in Vacuum Dark Energy Models

Abstract

Recently, Wang et al. (2014) and Salvatelli et al. (2014) have reported results showing that a late-time interaction between cold dark matter (CDM) and vacuum dark energy is favoured by current cosmological datasets and could alleviate the tension between the value of the Hubble constant obtained from Plank + WMAP polarisation data and that of the Hubble Space Telescope (HST). In this paper, we explore an alternative interacting vacuum dark energy model in which the net energy-momentum transfer is linear in the dark energy density and consider the behaviour for scalar perturbations in the conformal Newtonian gauge. Normalizing the energy densities to their present values, a positive interaction in the Friedmann Robertson Walker (FRW) background implies higher allowed values for the Hubble parameter, 𝐻0, and the Dark Matter (DM) density than the in non-interacting model. Perturbations in the DM density deviate highly from the standard non-interacting case for higher interaction strengths regardless of direction of the energy transfer while in the linear DM power spectrum shows a shift degenerate with bias in the standard case.