Scalar-induced gravitational waves from ghost inflation and parity violation
Sebastián García-Sáenz, Yizhou Lu, Zhiming Shuai
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 nondegenerate 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.