Cosmology of a Scalar Field Coupled to Matter and an Isotropy-Violating Maxwell Field

TL;DR

This paper explores how a scalar field coupled to matter and an anisotropic Maxwell field influences cosmological evolution, identifying solutions that align with observed isotropy and constraining model parameters based on CMB data.

Contribution

It introduces new anisotropic scaling solutions in scalar-vector coupled cosmologies and constrains their parameters using CMB quadrupole sensitivity.

Findings

Universe expands nearly isotropically despite anisotropic vector field

The matter-to-vector coupling ratio is constrained to be less than 10^(-5)

Viable cosmologies close to LCDM are found in strong vector coupling regimes

Abstract

Motivated by the couplings of the dilaton in four-dimensional effective actions, we investigate the cosmological consequences of a scalar field coupled both to matter and a Maxwell-type vector field. The vector field has a background isotropy-violating component. New anisotropic scaling solutions which can be responsible for the matter and dark energy dominated epochs are identified and explored. For a large parameter region the universe expands almost isotropically. Using that the CMB quadrupole is extremely sensitive to shear, we constrain the ratio of the matter coupling to the vector coupling to be less than 10^(-5). Moreover, we identify a large parameter region, corresponding to a strong vector coupling regime, yielding exciting and viable cosmologies close to the LCDM limit.