H. V. Ragavendra, Giulia Capurri, Alina Mierna, Gabriele Perna, Federico Semenzato, Nicola Bartolo, Daniele Bertacca, Lorenzo Valbusa Dall'Armi, Sabino Matarrese, Matteo Pegorin, Angelo Ricciardone

This chapter explores theoretical and observational strategies to use the stochastic gravitational-wave background detectable by Square Kilometre Array Observatory (SKAO) as a probe of precision cosmology. We detail the critical phenomenon of scalar-induced gravitational waves, demonstrating their unique features and their sensitivity to primordial non-Gaussianity on scales much smaller than those probed by the cosmic microwave background and large-scale structure. We investigate the phenomenology of parity violation in the early Universe through the chirality imprinted in the stochastic gravitational-wave background, demonstrating that a parity-odd primordial trispectrum can generate a detectable scale-dependent helicity. On the observational side, we point out that the standard gravitational-wave angular auto-correlation analysis is significantly limited by astrophysical shot noise. We show that cross-correlating the gravitational wave signal with independent large-scale structure tracers enhances the signal-to-noise ratio and allows us to isolate the astrophysical and cosmological components in the background. These results can be achieved only thanks to the enhanced sensitivity of SKAO, extensive sky coverage, and high angular resolution, which together make such targets observationally feasible.