Detectability of the effect of Inflationary non-Gaussianity on halo bias

TL;DR

The paper investigates how different inflationary non-Gaussianities imprint on the large-scale halo bias, extending the MV08 framework to non-local bispectrum shapes and including horizon-scale GR corrections. It derives the halo-bias correction through the scale-dependent function $\beta(k)$ that depends on the primordial bispectrum $B_{\Phi}$, and compares local, equilateral, enfolded, and GR-correction templates. The main result is that inflationary plus GR corrections yield a scale-dependent halo-bias signature that mimics local-type with an effective $f_{\rm NL}$ of order $-1.6$ on the relevant scales, while equilateral and enfolded shapes are harder to detect with halo bias alone. Forecasts for Euclid and LSST indicate $1$-to-$2.2$-sigma detections for the GR-type signal and substantial enfolded constraints ($\Delta f_{\rm NL}^{\rm enf}\sim 39$ for Euclid, $\sim 18$ for LSST), underscoring the complementary role of halo bias to CMB constraints for distinguishing inflationary models.

Abstract

We consider the description of the clustering of halos for physically-motivated types of non-Gaussian initial conditions. In particular we include non-Gaussianity of the type arising from single field slow-roll, multi fields, curvaton (local type), higher-order derivative-type (equilateral), vacuum-state modifications (enfolded-type) and horizon-scale GR corrections type. We show that large-scale halo bias is a very sensitive tool to probe non-Gaussianity, potentially leading, for some planned surveys, to a detection of non-Gaussianity arising from horizon-scale GR corrections. In tandem with cosmic microwave background constraints, the halo-bias approach can help enormously to discriminate among different shapes of non-Gaussianity and thus among models for the origin of cosmological perturbations.

Figures (1)

• Figure 1: The scale-dependence of the large-scale halo bias induced by non-zero bispectrum, indicated by the $\beta$ function of Eqs. 3 for the four types of non-Gaussianity discussed in the text. The solid line shows the absolute value of $\beta$ for the inflationary, GR correction large-scale structure bispectrum. Note that the quantity is actually negative. The dashed line shows $\beta$ for the local type of primordial non-Gaussianity for $f_{\rm NL}^{\rm loc}=1$ (the quantity is positive). It is clear that the scale-dependent bias effect due to the inflationary bispectrum mimics a local primordial non-Gaussianity with effective $f_{\rm NL}$$\sim -1$ at $k>0.02$$H$/Mpc and $\sim -1.6$ for $k<0.01$$h$/Mpc. The dot-dot-dot-dashed line shows the effect of equilateral non-Gaussianity for $f_{\rm NL}^{\rm eq}=1$ and the dotted line shows the enfolded-type with $f_{\rm NL}^{\rm enf}=1$.