Speaker
Description
Beyond two-point statistics, the galaxy bispectrum provides a sensitive probe of non-linear gravitational dynamics, redshift-space anisotropies, and physics beyond ΛCDM. We study redshift-space galaxy bispectrum multipoles as a probe of massive neutrinos and modified gravity, focusing on the Hu–Sawicki f(R) model. Using a spherical-harmonic decomposition of the bispectrum, we capture the full angular dependence induced by redshift-space distortions. We develop a perturbative framework incorporating neutrino-induced scale-dependent growth, modified second-order kernels, chameleon screening, tracer bias, Fingers-of-God damping, and shot noise. Both massive neutrinos and f(R) gravity imprint characteristic, configuration-dependent signatures, with the strongest effects arising in stretched and squeezed triangle configurations. For a total neutrino mass of 0.12 eV, deviations reach the percent level, while f(R) gravity produces 2–8% deviations for fR0 = 10⁻⁵ on intermediate scales. Forecasts for a Euclid-like survey show that the monopole and quadrupole multipoles dominate the signal, yielding signal-to-noise ratios of approximately 5 for neutrino effects and up to about 30 for modified gravity. Higher-order multipoles provide weaker but important information, highlighting the potential of the bispectrum as a complementary probe of new physics beyond ΛCDM.