Scalar-Induced Gravitational Waves from Ghost Inflation and Parity Violation

TL;DR

This paper computes scalar-induced gravitational waves in Ghost Inflation, highlighting the potential for parity-violating signals to serve as probes of early universe physics and parity violation during inflation.

Contribution

It introduces calculations of gravitational wave energy density including both power spectrum and trispectrum contributions, emphasizing parity-violating effects in Ghost Inflation.

Findings

Parity-even trispectrum contribution is suppressed by perturbativity constraints.

Parity-odd signals, though small, can be distinguished and may probe parity violation.

Parity-odd gravitational wave signals could be comparable to parity-even non-Gaussian signals.

Abstract

We calculate the scalar-induced gravitational wave energy density in the theory of Ghost Inflation, assuming scale invariance and taking into account both the power spectrum- and trispectrum-induced contributions. For the latter we consider the leading cubic and quartic couplings of the comoving curvature perturbation in addition to two parity-violating quartic operators. In the parity-even case, we find the relative importance of the trispectrum-induced signal to be suppressed by the requirement of perturbativity, strengthening a no-go theorem recently put forth. The parity-odd signal, even though also bound to be small, is non-degenerate with the Gaussian contribution and may in principle be comparable to the parity-even non-Gaussian part, thus potentially serving as a probe of the Ghost Inflation scenario and of parity violating physics during inflation.