Primordial Perturbations in Einstein-Aether and BPSH Theories

TL;DR

This paper investigates how primordial scalar and vector perturbations generated during inflation in Einstein-aether theories influence cosmic microwave background anisotropies, providing constraints on the theory's parameters.

Contribution

It offers a detailed analysis of primordial perturbations in Einstein-aether theories and extends the results to related Horava gravity models, including observational constraints.

Findings

Scalar and vector perturbations can significantly affect CMB anisotropies.

The primordial spectra depend on specific model parameters.

Constraints on Einstein-aether parameters are tightened based on observational data.

Abstract

We study the primordial perturbations generated during a stage of single-field inflation in Einstein-aether theories. Quantum fluctuations of the inflaton and aether fields seed long wavelength adiabatic and isocurvature scalar perturbations, as well as transverse vector perturbations. Geometrically, the isocurvature mode is the potential for the velocity field of the aether with respect to matter. For a certain range of parameters, this mode may lead to a sizable random velocity of the aether within the observable universe. The adiabatic mode corresponds to curvature perturbations of co-moving slices (where matter is at rest). In contrast with the standard case, it has a non-vanishing anisotropic stress on large scales. Scalar and vector perturbations may leave significant imprints on the cosmic microwave background. We calculate their primordial spectra, analyze their contributions to the temperature anisotropies, and formulate some of the phenomenological constraints that follow from observations. These may be used to further tighten the existing limits on the parameters for this class of theories. The results for the scalar sector also apply to the extension of Horava gravity recently proposed by Blas, Pujolas and Sibiriakov.