Nonlinear Evolution of Anisotropic Cosmological Power

TL;DR

This paper investigates how primordial power anisotropies evolve nonlinearly in the universe, finding that such anisotropies are significantly suppressed in the quasilinear regime, which impacts tests of statistical isotropy.

Contribution

It provides a third-order perturbation theory calculation of the nonlinear evolution of anisotropic primordial power spectra, highlighting suppression effects.

Findings

Primordial power anisotropies are suppressed by less than 7% in the quasilinear regime.

Skewness in anisotropic models differs by no more than 1% from isotropic models.

Results inform the interpretation of galaxy survey data for testing isotropy.

Abstract

There has been growing interest in the possibility of testing more precisely the assumption of statistical isotropy of primordial density perturbations. If it is to be tested with galaxy surveys at distance scales <~ 10 Mpc, then nonlinear evolution of anisotropic power must be understood. To this end, we calculate the angular dependence of the power spectrum to third order in perturbation theory for a primordial power spectrum with a quadrupole dependence on the wavevector direction. Our results suggest that primordial power anisotropies will be suppressed by <~ 7% in the quasilinear regime. We also show that the skewness in the statistically anisotropic theory differs by no more than 1% from that in the isotropic theory.