Constraints on primordial density perturbations from induced gravitational waves

TL;DR

This paper explores how the stochastic background of gravitational waves generated in the early universe can constrain the amplitude of primordial density perturbations on small scales beyond current observational limits.

Contribution

It introduces a method to use gravitational wave backgrounds to set upper bounds on small-scale primordial density perturbations, improving constraints with future detectors.

Findings

Current data place weak upper bounds on small-scale perturbations.

Future detectors like BBO and DECIGO will significantly tighten these constraints.

Gravitational waves serve as a novel probe for early universe density fluctuations.

Abstract

We consider the stochastic background of gravitational waves produced during the radiation-dominated hot big bang as a constraint on the primordial density perturbation on comoving length scales much smaller than those directly probed by the cosmic microwave background or large-scale structure. We place weak upper bounds on the primordial density perturbation from current data. Future detectors such as BBO and DECIGO will place much stronger constraints on the primordial density perturbation on small scales.