On the viability of a certain vector-tensor theory of gravitation

TL;DR

This paper evaluates a vector-tensor gravity theory's cosmological viability, showing it conflicts with observations at high vector field energy densities but aligns at lower densities, potentially explaining CMB anomalies.

Contribution

It demonstrates the conditions under which the vector-tensor theory is compatible with cosmological observations and explores its unique predictions for vector modes.

Findings

High vector field energy density conflicts with observations.

Low energy density makes the theory compatible with data.

Unique evolution of vector modes may explain CMB anomalies.

Abstract

A certain vector-tensor theory is revisited. Our attention is focused on cosmology. Against previous suggestions based on preliminary studies, it is shown that, if the energy density of the vector field is large enough to play the role of the dark energy and its fluctuations are negligible, the theory is not simultaneously compatible with current observations on: supernovae, the cosmic microwave background (CMB) anisotropy, and the power spectrum of the energy density fluctuations. However, for small enough energy densities of the vector field, the theory becomes compatible with all the above observations and, moreover, it leads to an interesting evolution of the so-called vector cosmological modes. This evolution appears to be different from that of general relativity, and the difference might be useful to explain the anomalies in the low order CMB multipoles.