Cosmology in generalized Proca theories

Abstract

We consider a massive vector field with derivative interactions that\npropagates only the 3 desired polarizations (besides two tensor polarizations\nfrom gravity) with second-order equations of motion in curved space-time. The\ncosmological implications of such generalized Proca theories are investigated\nfor both the background and the linear perturbation by taking into account the\nLagrangian up to quintic order. In the presence of a matter fluid with a\ntemporal component of the vector field, we derive the background equations of\nmotion and show the existence of de Sitter solutions relevant to the late-time\ncosmic acceleration. We also obtain conditions for the absence of ghosts and\nLaplacian instabilities of tensor, vector, and scalar perturbations in the\nsmall-scale limit. Our results are applied to concrete examples of the general\nfunctions in the theory, which encompass vector Galileons as a specific case.\nIn such examples, we show that the de Sitter fixed point is always a stable\nattractor and study viable parameter spaces in which the no-ghost and stability\nconditions are satisfied during the cosmic expansion history.\n