Cosmic Microwave Background Anisotropy from Nonlinear Structures in Accelerating Universes

TL;DR

This paper investigates how nonlinear cosmic structures like voids and lumps affect CMB anisotropy in accelerating universes, revealing potential observable temperature variations caused by large-scale nonlinear features.

Contribution

It provides a comprehensive numerical analysis of nonlinear structures' effects on CMB anisotropy, extending previous linear and thin-shell approximation studies.

Findings

Nonlinear voids cause redshifts in passing CMB photons.

Lumps near us blueshift or redshift CMB photons depending on proximity.

Large quasi-linear voids/lumps could produce detectable temperature variations in the CMB.

Abstract

We study the cosmic microwave background (CMB) anisotropy due to spherically symmetric nonlinear structures in flat universes with dust and a cosmological constant. By modeling a time-evolving spherical compensated void/lump by Lemaitre-Tolman-Bondi spacetimes, we numerically solve the null geodesic equations with the Einstein equations. We find that a nonlinear void redshifts the CMB photons that pass through it regardless of the distance to it. In contrast, a nonlinear lump blueshifts (or redshifts) the CMB photons if it is located near (or sufficiently far from) us. The present analysis comprehensively covers previous works based on a thin-shell approximation and a linear/second order perturbation method and the effects of shell thickness and full nonlinearity. Our results indicate that, if quasi-linear and large ($>100$Mpc) voids/lumps would exist, they could be observed as cold or hot spots with temperature variance $>10^{-5}$K in the CMB sky.