Explicit spacetime-symmetry breaking and the dynamics of primordial fields

TL;DR

This paper investigates how explicit spacetime-symmetry breaking affects primordial tensor fluctuations, revealing modifications in propagation speed, power spectrum amplitude, and phase shifts during radiation domination, with constraints from recent gravity speed measurements.

Contribution

It introduces an effective-field theory framework for Lorentz/CPT violation impacting primordial tensor modes, providing new constraints and insights into inflationary dynamics.

Findings

Graviton remains massless despite symmetry breaking.

Tensor mode speed is modified, constrained to ~10^{-15}.

Primordial power spectrum shows amplitude modifications and phase shifts.

Abstract

We study the effects of explicit spacetime-symmetry breaking on primordial tensor fluctuations using an effective-field theory for Lorentz/CPT violation. We find that the graviton is still massless, but that the propagation speed of tensor modes is modified, and we obtain a constraint on the coefficient determining the symmetry breaking on the order of $10^{-15}$ from the recent measurements of the speed of gravity. Due to the symmetry breaking, the de-Sitter phase is modified, and during this inflationary epoch, the power spectrum assumes a slow oscillation around the general-relativity limit; further, we find that the primordial tensor power spectrum retains its scale invariance, but that the amplitude is modified. We also find that the modes which become subhorizon during radiation domination acquire a phase shift proportional to the coefficient for Lorentz violation.