Scalar-induced gravitational waves from coherent initial states

TL;DR

This paper explores how non-standard initial quantum states during inflation can induce statistical inhomogeneity, anisotropy, and parity violation in scalar-induced gravitational waves, providing new observational probes.

Contribution

It introduces a model where primordial scalar fluctuations from a coherent state lead to unique scale-dependent and polarization features in gravitational waves.

Findings

Detection of signatures could reveal the statistical nature of primordial fluctuations

Statistical inhomogeneity causes scale-dependent features in gravitational wave correlations

Parity violation and polarization correlations are possible in the gravitational wave background

Abstract

We investigate the impact of statistical inhomogeneity and anisotropy in primordial scalar perturbations on the scalar-induced gravitational waves (SIGW). Assuming inflationary quantum fluctuations originate from a coherent state, the resulting primordial scalar perturbations acquire a non-zero space-dependent mean, violating statistical homogeneity, statistical isotropy, and parity. As a consequence of statistical inhomogeneities, SIGW acquires distinct scale-dependent features in its correlation function. Statistical anisotropies further lead to possible parity violation and correlation between different polarization modes in the tensor perturbations. Therefore, detection of these signatures in the stochastic gravitational wave background would offer probes to the statistical nature of primordial scalar perturbations beyond the scales accessible to CMB observations.