Speaker
Description
The bispectrum of galaxy number counts is a key probe of large-scale structure, offering sensitivity to nonlinear gravitational evolution, galaxy bias, and primordial non-Gaussianity (PNG). In this talk, I present the first full-sky computation of the angular bispectrum in second-order perturbation theory without the Limber approximation, formulated for finite redshift bins via tomographic spherical harmonics. The framework incorporates all Newtonian contributions (density, redshift-space distortions, quadratic terms), non-integrated relativistic projection effects, and dynamical general relativistic and radiation corrections. Notably, radiation effects dominate the relativistic signal in the squeezed limit at $z \sim 2$, exceeding projection effects by over an order of magnitude. I further extend this framework to include galaxy bias and the three standard PNG shapes (local, equilateral, orthogonal), demonstrating how unmodeled relativistic effects can contaminate $f_{\rm NL}$ estimates and discussing the second-order scale-dependent biases. Applications to forecasts for the Square Kilometre Array are discussed. The corresponding code, \texttt{ang_bispec}, is publicly available.