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Multitracer technique for galaxy bispectrum - An application to constraints on non-local primordial non-Gaussianities -

Daisuke Yamauchi, Shuichiro Yokoyama, Keitaro Takahashi

TL;DR

This paper investigates constraining non-local primordial non-Gaussianities using the galaxy bispectrum with a multitracer approach. It derives the monopole expressions for the redshift-space bispectrum across multiple tracers and formulates a Fisher-matrix framework to forecast constraints on $f_{NL}^{eq}$ and $f_{NL}^{orth}$. Forecasts for Euclid and the SKA indicate that two-tracer analyses can achieve $ ext{approximately } ext{23–25}$ for $f_{NL}^{eq}$ and $ ext{around } ext{10–13}$ for $f_{NL}^{orth}$, highlighting substantial cosmic-variance reduction and competitive PNG sensitivity relative to CMB limits. The work emphasizes the importance of high galaxy density for effective CV cancellation and discusses caveats related to modeling systematics and halo-mass estimation in future surveys.

Abstract

We explore the use of galaxy bispectra with multitracer technique as a possible probe of primordial non-Gaussianities. We forecast future constraints on non-linearity parameters, $f_{\rm NL}^{\rm eq}$ and $f_{\rm NL}^{\rm orth}$, which respectively characterize the equilateral- and orthogonal-types primordial bispectra, and show that the multitracer analysis would be effective with reducing the cosmic-variance noise if the number density of galaxies is high enough. We find that the measurement of galaxy bispectrum by future galaxy surveys can reach the constraints on the non-local type primordial non-Gaussianities to the level severer than current one which has been obtained by cosmic microwave background observations.

Multitracer technique for galaxy bispectrum - An application to constraints on non-local primordial non-Gaussianities -

TL;DR

This paper investigates constraining non-local primordial non-Gaussianities using the galaxy bispectrum with a multitracer approach. It derives the monopole expressions for the redshift-space bispectrum across multiple tracers and formulates a Fisher-matrix framework to forecast constraints on and . Forecasts for Euclid and the SKA indicate that two-tracer analyses can achieve for and for , highlighting substantial cosmic-variance reduction and competitive PNG sensitivity relative to CMB limits. The work emphasizes the importance of high galaxy density for effective CV cancellation and discusses caveats related to modeling systematics and halo-mass estimation in future surveys.

Abstract

We explore the use of galaxy bispectra with multitracer technique as a possible probe of primordial non-Gaussianities. We forecast future constraints on non-linearity parameters, and , which respectively characterize the equilateral- and orthogonal-types primordial bispectra, and show that the multitracer analysis would be effective with reducing the cosmic-variance noise if the number density of galaxies is high enough. We find that the measurement of galaxy bispectrum by future galaxy surveys can reach the constraints on the non-local type primordial non-Gaussianities to the level severer than current one which has been obtained by cosmic microwave background observations.

Paper Structure

This paper contains 4 sections, 17 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Bispectrum with multiple tracers
  3. Fisher analysis
  4. Summary

Figures (3)

  • Figure 1: $1\sigma$ marginalized errors in as a function of comoving galaxy number density, $f_{\rm NL}^{\rm eq}$ (top), $f_{\rm NL}^{\rm orth}$ (middle) and $f_{\rm NL}^{\rm local}$ (bottom) for survey with $V_{\rm survey}=10\,h^{-3}{\rm Gpc}^3$ and $z=1$.
  • Figure 2: Same as Fig. \ref{['fig:plot_sigma_fNL_ng']} but for $z=2$. The green dotted lines represent the current limit from Planck Ade:2015avaAde:2013ydc.
  • Figure 3: Forecast $1\sigma$ marginalized contours in $(f_{\rm NL}^{\rm eq},b_1^{(1)})$ (left), $(f_{\rm NL}^{\rm orth},b_1^{(1)})$ (right) planes.