Anisotropies in Scalar-Induced Gravitational-Wave Background from Inflaton-Curvaton Mixed Scenario with Sound Speed Resonance

TL;DR

This paper introduces a model where sound speed resonance in an inflaton-curvaton scenario amplifies scalar-induced gravitational waves, creating large anisotropies that could be detected by future GW observatories, revealing early universe physics.

Contribution

It presents a novel mechanism for generating large anisotropies in SIGWs through sound speed resonance and primordial non-Gaussianity in an inflaton-curvaton model.

Findings

Potential detection of anisotropies by DECIGO.

Enhanced energy-density spectrum at resonant frequencies.

Large angular power spectrum amplitude of SIGWs.

Abstract

We propose a new model to generate large anisotropies in the scalar-induced gravitational wave (SIGW) background via sound speed resonance in the inflaton-curvaton mixed scenario. Cosmological curvature perturbations are not only exponentially amplified at a resonant frequency, but also preserve significant non-Gaussianity of local type described by $f_{\mathrm{nl}}$. Besides a significant enhancement of energy-density fraction spectrum, large anisotropies in SIGWs can be generated, because of super-horizon modulations of the energy density due to existence of primordial non-Gaussianity. A reduced angular power spectrum $\tilde{C}_{\ell}$ could reach an amplitude of $[\ell(\ell+1)\tilde{C}_{\ell}]^{1/2} \sim 10^{-2}$, leading to potential measurements via planned gravitational-wave detectors such as DECIGO. The large anisotropies in SIGWs would serve as a powerful probe of the early universe, shedding new light on the inflationary dynamics, primordial non-Gaussianity, and primordial black hole dark matter.