Spectator stresses and CMB observables

TL;DR

This paper investigates how spectator anisotropic stresses influence large-scale curvature perturbations and CMB observables during the matter-radiation transition, revealing unique signatures different from standard adiabatic and non-adiabatic modes.

Contribution

It provides a detailed analysis of the impact of subdominant spectator anisotropic stresses on CMB anisotropies and establishes their distinct observational signatures.

Findings

Spectator anisotropic stresses alter the shape and phase of CMB fluctuations.

The initial conditions are constrained by the momentum and Einstein-Boltzmann equations.

CMB signatures differ from those of adiabatic and non-adiabatic modes.

Abstract

The large-scale curvature perturbations induced by spectator anisotropic stresses are analyzed across the matter-radiation transition. It is assumed that the anisotropic stress is associated with a plasma component whose energy density is subdominant both today and prior to photon decoupling. The enforcement of the momentum constraint and the interplay with the neutrino anisotropic stress determine the regular initial conditions of the Einstein-Boltzmann hierarchy. The Cosmic Microwave Background observables have shapes and phases which differ both from the ones of the conventional adiabatic mode as well as from their non-adiabatic counterparts.