Nonlinear modulation of the HI power spectrum on ultra-large scales. I

TL;DR

This paper investigates how nonlinear effects, especially from weak lensing, bias the measurement of the HI power spectrum on ultra-large scales in intensity mapping, affecting cosmological inferences.

Contribution

It demonstrates the importance of renormalizing perturbations at higher order to accurately interpret ultra-large scale measurements in HI intensity mapping.

Findings

Second-order effects from weak lensing dominate nonlinear contributions at high redshift.

Renormalization alters the mean brightness temperature and evolution bias.

Nonlinear effects introduce a white noise-like term that impacts large-scale analyses.

Abstract

Intensity mapping of the neutral hydrogen brightness temperature promises to provide a three-dimensional view of the universe on very large scales. Nonlinear effects are typically thought to alter only the small-scale power, but we show how they may bias the extraction of cosmological information contained in the power spectrum on ultra-large scales. For linear perturbations to remain valid on large scales, we need to renormalize perturbations at higher order. In the case of intensity mapping, the second-order contribution to clustering from weak lensing dominates the nonlinear contribution at high redshift. Renormalization modifies the mean brightness temperature and therefore the evolution bias. It also introduces a term that mimics white noise. These effects may influence forecasting analysis on ultra-large scales.