Anisotropies in scalar-induced gravitational-wave background from inflaton-curvaton mixed scenario with sound speed resonance

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 fₙₗ. 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 C_ could reach an amplitude of [(+1)C_]1/2~10^-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.