Infrared divergence of pure Einstein gravity contributions to cosmological density power spectrum

TL;DR

This paper investigates Einstein gravity's effects on the cosmological density power spectrum, revealing negligible contributions on small scales but dominant effects on large scales, leading to an infrared divergence at third order.

Contribution

It demonstrates the scale-dependent significance of Einstein gravity in the power spectrum and identifies an infrared divergence at third order in perturbation theory.

Findings

Einstein gravity contribution is negligible at small scales.

Einstein gravity dominates at large scales, surpassing linear-order effects.

Infrared divergence arises in the power spectrum due to third-order Einstein gravity effects.

Abstract

We probe the pure Einstein's gravity contributions to the second-order density power spectrum. In the small-scale, we discover that the Einstein's gravity contribution is negligibly small. This guarantees that Newton's gravity is sufficient to handle the baryon acoustic oscillation scale. In the large scale, however, we discover that the Einstein's gravity contribution to the second-order power spectrum dominates the linear-order power spectrum. Thus, pure Einstein gravity contribution appearing in the third-order perturbation leads to an infrared divergence in the power spectrum.