Hunting high and low: disentangling primordial and late-time non-Gaussianity with cosmic densities in spheres

Abstract

Non-Gaussianities of dynamical origin are disentangled from primordial ones using the formalism of large deviation statistics with spherical collapse dynamics. This is achieved by relying on accurate analytical predictions for the one-point probability distribution function (PDF) and the two-point clustering of spherically-averaged cosmic densities (sphere bias). Sphere bias extends the idea of halo bias to intermediate density environments and voids as underdense regions. In the presence of primordial non-Gaussianity, sphere bias displays a strong scale dependence relevant for both high and low density regions, which is predicted analytically. The statistics of densities in spheres are built to model primordial non-Gaussianity via an initial skewness with a scale-dependence that depends on the bispectrum of the underlying model. The analytical formulas with the measured nonlinear dark matter variance as input are successfully tested against numerical simulations. For local non-Gaussianity with a range from f NL = −100 to +100 they are found to agree within 2% or better for densities ρ ∈ [0.5, 3] in spheres of radius 15 Mpc/h down to z = 0.35. The validity of the large deviation statistics formalism is thereby established for all observationally relevant local-type departures from perfectly Gaussian initial conditions. The corresponding estimators for the amplitude of the nonlinear variance σ 8 and primordial skewness f NL are validated using a fiducial joint maximum likelihood experiment. The influence of observational effects and the prospects for a future detection of primordial non-Gaussianity from joint one-and two-point densities-in-spheres statistics are discussed.

The Hunt for Primordial Interactions in the Large-Scale Structures of the Universe

“…This assumption has been extensively analyzed in numerical N-body simulations and shown to work rather well for a wide range of masses [153][154][155]222]. Several authors have developed the technical tools to deal with local density maxima in the presence of non-Gaussian initial conditions [159,196,199,200,203,204]. Here we want to collect all their progresses and include them in the effort of combining the peak model and the excursion set approach.…”

The PDF perspective on the tracer-matter connection: Lagrangian bias and non-Poissonian shot noise

“…This is somewhat unnatural, because standard methods to model the matter density PDF are typically built around the symmetric collapse of a leading order (saddle-point) configuration of the density field (e.g. Bernardeau 1994Bernardeau , 1995Valageas 2002a;Bernardeau et al 2015;Uhlemann et al 2016Uhlemann et al , 2018bFriedrich et al 2020a) which would seem to suggest a Lagrangian point-of-view.…”

Post-Born corrections to the one-point statistics of (CMB) lensing convergence obtained via large deviation theory

“…The extrapolation to small non zero values is then performed without prior knowledge on the range of validity one can reach. Fortunately, it has been shown to probe accurately the mildly non-linear regime up to rather surprisingly small scales (few megaparsecs corresponding to a typical amplitude of den-4 Primordial non-Gaussianities could also straightforwardly be accounted for in this formalism as shown by Uhlemann et al (2018). (53).…”