Orateur
Description
Primordial non-Gaussianity (PNG) is one of the few accessible windows into inflation: a significant detection of local PNG, $\left\vert f_\mathrm{NL}^\mathrm{loc} \right\vert \gtrsim 1$, would rule out standard single-field slow roll inflation. The tightest current constraints come from the CMB bispectrum, and are close to the cosmic variance limit. Three-dimensional galaxy surveys such as DESI offer tremendously more modes to exploit, and $f_\mathrm{NL}^\mathrm{loc}$ leaves a distinct signature in the large scales of the galaxy power spectrum through the scale-dependent bias. DESI is forecast to reach CMB-competitive constraints with five years of data.
Measuring PNG via the scale-dependent bias requires rigorous modeling of the large scales of the power spectrum (survey geometry, integral constraints) and good control of observational systematics (imaging systematics). Since the first DESI $f_\mathrm{NL}^\mathrm{loc}$ constraints with DR1 in 2024, the collaboration has substantially revised the modeling of these effects. I will present an overview of the DESI DR2 PNG pipeline, its validation, and the expected $f_\mathrm{NL}^\mathrm{loc}$ constraints. In particular, I will introduce a new forward model method for the power spectrum which accounts simultaneously for survey geometry, integral constraints, and power loss from imaging systematics mitigation, without approximation.