Second Order Gravitational Effects on CMB Temperature Anisotropy in Lambda dominated flat universes

TL;DR

This paper investigates second order gravitational effects of local inhomogeneities on CMB temperature anisotropies in flat universes with a cosmological constant, finding that these effects can be significant around redshift 1.

Contribution

It provides a detailed analysis of second order gravitational effects on CMB anisotropies, highlighting their potential significance near redshift 1 in Lambda dominated flat universes.

Findings

Second order effects are negligible when inhomogeneities are much smaller than the horizon.

Second order effects can enhance or suppress the linear ISW effect depending on the inhomogeneity type.

Temperature fluctuations peak before matter-$ ext{Lambda}$ equality for certain inhomogeneity parameters.

Abstract

We study second order gravitational effects of local inhomogeneities on the cosmic microwave background radiation in flat universes with matter and a cosmological constant $\Lambda$. We find that the general relativistic correction to the Newtonian approximation is negligible at second order provided that the size of the inhomogeneous region is sufficiently smaller than the horizon scale. For a spherically symmetric top-hat type quasi-linear perturbation, the first order temperature fluctuation corresponding to the linear integrated Sachs-Wolfe (ISW) effect is enhanced(suppressed) by the second order one for a compensated void(lump). As a function of redshift of the local inhomogeneity, the second order temperature fluctuations due to evolution of the gravitational potential have a peak before the matter-$\Lambda$ equality epoch for a fixed comoving size and a density contrast. The second order gravitational effects from local quasi-linear inhomogeneities at a redshift z~1 may significantly affect the cosmic microwave background.