Speaker
Description
Scalar Induced Gravitational Waves (SIGW) are generated at second order in perturbation theory and to achieve observational relevance, inflationary dynamics must evade the standard slow-roll scenario at small scales, generating large curvature perturbations following strongly non-gaussian statistics. We propose a method to efficiently compute the SIGW spectrum including arbitrary non-gaussianities. First, we solve the wave equation adopting semi-analytic methods; this result into an expression involving integrals in Fourier space impossible to solve directly on a lattice, a bottleneck that we overcome by recasting these integrals
as a sum of $N_\alpha \sim 50$ convolutions, each of which can be computed efficiently with FFT methods. Finally, the power spectrum is measured directly from the lattice realization. We implement this in FLAN-SIGW, a GPU-accelerated code able to compute fully non-perturbative, non-Gaussian SIGW spectra in seconds with an error within $\sim 10\%$ with modest computational resources. In this first implementation, in order to assess the performance of the method, we adopt a standard radiation-dominated background with $w = 1/3$.