The Integrated Bispectrum and Beyond

TL;DR

This paper generalizes the position-dependent power spectrum to higher orders, linking it to known statistics like the bispectrum and skew-spectrum, and explores its applications in 3D and 2D cosmological data analysis.

Contribution

It introduces a higher-order generalization of the position-dependent spectrum, clarifies its relation to other statistics, and extends its application to velocity divergence, mixed spectra, and projected maps.

Findings

Polyspectra in the soft limit relate to lower order spectra with renormalized amplitudes.

Extension of the concept to bispectrum of velocity divergence and mixed spectra.

Application to 2D projected maps and cross-spectra in cosmology.

Abstract

The position-dependent power spectrum has been recently proposed as a descriptor of gravitationally induced non-Gaussianity in galaxy clustering, as it is sensitive to the "soft limit" of the bispectrum (i.e. when one of the wave number tends to zero). We generalise this concept to higher order and clarify their relationship to other known statistics such as the skew-spectrum, the kurt-spectra and their real-space counterparts the cumulants correlators. Using the {\em Hierarchical Ansatz} (HA) as a toy model for the higher order correlation hierarchy, we show how in the soft limit, polyspectra at a given order can be identified with lower order polyspectra with the same geometrical dependence but with {\em renormalised} amplitudes expressed in terms of amplitudes of the original polyspectra. We extend the concept of position-dependent bispectrum to bispectrum of the divergence of the velocity field $\Theta$ and mixed multispectra involving $\delta$ and $\Theta$ in the 3D perturbative regime. To quantify the effects of transients in numerical simulations, we also present results for lowest order in Lagrangian perturbation theory (LPT) or the Zel'dovich approximation (ZA). Finally, we discuss how to extend the position-dependent spectrum concept to encompass cross-spectra. And finally study the application of this concept to two dimensions (2D), for projected galaxy maps, convergence $\kappa$ maps from weak-lensing surveys or maps of CMB secondaries e.g. the frequency cleaned $y$ - parameter maps of thermal Sunyaev-Zel'dovich (tSZ) effect from CMB surveys.