Impact of trans-Planckian quantum noise on the Primordial Gravitational Wave spectrum

TL;DR

This paper studies how stochastic quantum noise from trans-Planckian effects influences the primordial gravitational wave spectrum during inflation, modeling it via a black hole gas and Hawking radiation, and finds it preserves scale invariance.

Contribution

It introduces a model of trans-Planckian quantum noise affecting inflationary gravitational waves, linking black hole physics to primordial spectrum modifications.

Findings

The noise leads to a scale-invariant tensor spectrum.

Amplitude depends on the ratio of Lambda to the Planck scale.

Standard evolution resumes at later times.

Abstract

We investigate the impact of stochastic quantum noise due to trans--Planckian effects on the primordial power spectrum for gravity waves during inflation. Given an energy scale Lambda, expected to be close to the Planck scale m_Pl and larger than the Hubble scale H, this noise is described in terms of a source term in the evolution equation for comoving modes k which changes its amplitude growth from early times as long as the mode physical wavelength is smaller than Lambda^-1. We model the source term as due to a gas of black holes in the trans--Planckian regime and the corresponding Hawking radiation. In fact, for energy scales larger than, or of the order of Lambda, it is expected that trapped surfaces may form due to large energy densities. At later times the evolution then follows the standard sourceless evolution. We find that this mechanism still leads to a scale-invariant power spectrum of tensor perturbations, with an amplitude that depends upon the ratio Lambda/m_Pl.