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arXiv · 2410.18039

Local Primordial Non-Gaussian Bias at the Field Level

James M. Sullivan·Shi-Fan Chen
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Abstract

Local primordial non-Gaussianity (LPNG) couples long-wavelength cosmological fluctuations to the short-wavelength behavior of galaxies. This coupling is encoded in bias parameters including $b_ϕ$ and $b_{δϕ}$ at linear and quadratic order in the large-scale biasing framework. We perform the first field-level measurement of $b_ϕ$ and $b_{δϕ}$ using Lagrangian bias and non-linear displacements from N-body simulations. We compare our field level measurements with universality predictions and separate universe results, finding qualitative consistency, but disagreement in detail. We also quantify the information on $f_{\mathrm{NL}}^{(\mathrm{loc})}$ available in the field given various assumptions on knowledge of $b_ϕ$ at fixed initial conditions. We find that it is not possible to precisely constrain $f_{\mathrm{NL}}^{(\mathrm{loc})}$ when marginalizing over $b_ϕ f_{\mathrm{NL}}^{(\mathrm{loc})}$ even at the field level, observing a 2-3X degradation in constraints between a linear and quadratic biasing model on perturbative field-level mocks, suggesting that a $b_ϕ$ prior is necessary to meaningfully constrain $f_{\mathrm{NL}}^{(\mathrm{loc})}$ at the field level even in this idealized scenario. For simulated dark matter halos, the pure $f_{\mathrm{NL}}^{(\mathrm{loc})}$ constraints from both linear and quadratic field-level models appear biased when marginalizing over bias parameters including $b_ϕ$ and $b_{δϕ}$ due largely to the $f_{\mathrm{NL}}^{(\mathrm{loc})} - b_ϕ$ degeneracy. Our results are an important consistency test of the large-scale bias framework for LPNG and highlight the importance of physically motivated priors on LPNG bias parameters for future surveys.

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James M. Sullivan, Shi-Fan Chen. 2025-02-09. Local Primordial Non-Gaussian Bias at the Field Level. https://arxiv.org/abs/2410.18039

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