CMB Polarization in Einstein-Aether Theory

TL;DR

This paper investigates how Einstein-aether theory, which modifies the vector sector of gravity, affects CMB polarization, revealing that vector perturbations can produce a dominant B-mode signal surpassing inflationary gravitational waves.

Contribution

It derives the perturbation equations for the aether vector field and computes the resulting CMB B-mode polarization, highlighting the potential observational signatures of Einstein-aether theory.

Findings

Aether vector perturbations can generate a B-mode polarization signal stronger than inflationary gravitational waves.

The shape of the B-mode spectrum can be analytically understood using the tight coupling approximation.

The modified CAMB code enables precise computation of the polarization spectrum in Einstein-aether theory.

Abstract

We study the impact of modifying the vector sector of gravity on the CMB polarization. We employ the Einstein-aether theory as a concrete example. The Einstein-aether theory admits dynamical vector perturbations generated during inflation, leaving imprints on the CMB polarization. We derive the perturbation equations of the aether vector field in covariant formalism and compute the CMB B-mode polarization using the modified CAMB code. It is found that the amplitude of the B-mode signal from the aether field can surpass the one from the inflationary gravitational waves. The shape of the spectrum is clearly understood in an analytic way using the tight coupling approximation.