Quijote-PNG: Quasi-maximum Likelihood Estimation of Primordial Non-Gaussianity in the Nonlinear Dark Matter Density Field

Abstract

Future large-scale structure surveys are expected to improve current bounds on primordial non-Gaussianity (PNG), with a significant impact on our understanding of early universe physics. The level of such improvements will however strongly depend on the extent to which late-time nonlinearities erase the PNG signal on small scales. In this work, we show how much primordial information remains in the bispectrum of the nonlinear dark matter density field by implementing a new, simulation-based methodology for joint estimation of PNG amplitudes (f NL) and standard Lambda cold dark matter parameters. The estimator is based on optimally compressed statistics, which, for a given input density field, combine power spectrum and modal bispectrum measurements, and numerically evaluate their covariance and their response to changes in cosmological parameters. In this first analysis, we focus on the matter density field, and we train and validate the estimator using a large suite of N-body simulations (Quijote-png), including different types of PNG (local, equilateral, orthogonal). We explicitly test the estimator’s unbiasedness, optimality, and stability with respect to changes in the total number of input realizations. While the dark matter power spectrum itself contains negligible PNG information, as expected, including it as an ancillary statistic increases the PNG information content extracted from the bispectrum by a factor of order 2. As a result, we prove the capability of our approach to optimally extract PNG information on nonlinear scales beyond the perturbative regime, up to k max = 0.5 h Mpc − 1 . At the same time, we discuss the significant information on cosmological parameters contained on these scales.

Quijote-PNG: Simulations of Primordial Non-Gaussianity and the Information Content of the Matter Field Power Spectrum and Bispectrum

“…Our simulations allow us to extend the range of scales used in our analysis beyond the perturbative scales used in most advanced forecasts and analyses (e.g., Karagiannis et al 2018;Cabass et al 2022a;D'Amico et al 2022). This analysis, along with our companion paper (Jung et al 2022), are the first investigations of this kind. Our results show that significant gains can be made by including modes up to k h 0.3 Mpc max 1 ~» -; after this, the improvements are less dramatic.…”

“…Importantly, the combined power spectrum and bispectrum analysis leads to significant improvements over analyses of either probe alone. This is explored more in Jung et al (2022).…”

“…This paper and our companion paper, Jung et al (2022), are the first two in a series dedicated to investigating how we can learn more about primordial non-Gaussianity from upcoming measurements of the LSS.…”

“…In our companion paper, Jung et al (2022), we explore the properties of matter power spectrum and bispectrum from a different and complementary perspective: we use the modal bispectrum (Fergusson et al 2012;Schmittfull et al 2013) to measure the matter bispectrum and then develop and validate a set of optimal compressed statistics, which enable the information in the matter power spectrum and bispectrum to be captured within a data vector of length the number of parameters. Additionally, the Jung et al (2022) analysis focuses on measurements at z = 1.0, the redshift range relevant for upcoming surveys such as Euclid (Amendola et al 2018), whereas here we examine z = 0.0. Through this complementarity, we can better understand the importance of small-scale information across redshifts.…”

The Cosmic Graph: Optimal Information Extraction from Large-Scale Structure using Catalogues

“…Cosmological parameter constraints from void catalogues, here the duals to halo graphs, might elucidate complementary constraints to those obtained here (Kreisch et al 2021). Coulton et al (2022) and Jung et al (2022) recently investigated bispectrum statistics from n-body primordial nongaussianity (pNG) simulations in the Quijote suite to investigate propagation of pNG to late-time cosmological structure. A complementary study using gIMNNs might pick up signatures not isolated in the bispectrum framework.…”