Robust neural network-enhanced estimation of local primordial non-Gaussianity
Utkarsh Giri, Moritz Münchmeyer, Kendrick M. Smith
Abstract
When applied to the nonlinear matter distribution of the universe, neural networks have been shown to be very statistically sensitive probes of cosmological parameters, such as the linear perturbation amplitude ${\ensuremath{\sigma}}_{8}$. However, when used as a ``black box,'' neural networks are not robust to baryonic uncertainty. We propose a robust architecture for constraining primordial non-Gaussianity ${f}_{NL}$, by training a neural network to locally estimate ${\ensuremath{\sigma}}_{8}$, and correlating these local estimates with the large-scale density field. We apply our method to $N$-body simulations, and show that $\ensuremath{\sigma}({f}_{NL})$ is 3.5 times better than the constraint obtained from a standard halo-based approach. We show that our method has the same robustness property as large-scale halo bias: baryonic physics can change the normalization of the estimated ${f}_{NL}$, but cannot change whether ${f}_{NL}$ is detected.