Generation of Curvature Perturbations with Extra Anisotropic Stress

TL;DR

This paper investigates how extra anisotropic stress, such as from dark radiation, influences curvature perturbations and the CMB spectrum, revealing potential residual effects that could impact cosmological parameter estimation.

Contribution

It introduces a model for extra anisotropic stress affecting curvature perturbations and demonstrates its potential to produce residual CMB spectra similar to observations.

Findings

Cancellation of neutrino and extra anisotropic stress can produce residual curvature perturbations.

Residual perturbations may mimic observed CMB power spectrum.

Implications for cosmological parameter estimation from CMB data.

Abstract

We study the evolution of curvature perturbations and the cosmic microwave background (CMB) power spectrum in the presence of an hypothesized extra anisotropic stress which might arise, for example, from the dark radiation term in brane-world cosmology. We evolve the scalar modes of such perturbations before and after neutrino decoupling and analyze their effects on the CMB spectrum. A novel result of this work is that the cancellation of the neutrino and extra anisotropic stress could lead to a spectrum of residual curvature perturbations which is similar to the observed CMB power spectrum. This implies a possible additional consideration in the determination of cosmological parameters from the CMB analysis.