Testing Multi-Field Inflation with Galaxy Bias

TL;DR

This paper explores how future galaxy bias measurements can test multi-field inflation models by examining the relationship between tauNL and fNL, highlighting the challenges and requirements for such tests.

Contribution

It demonstrates that multi-tracer galaxy surveys can potentially test the tauNL and fNL inequality, providing a new method to validate multi-field inflation models.

Findings

Testing multi-field inflation requires tauNL~1e5 with fNL~10.

Disproving multi-field models is difficult unless |fNL| > 80.

Multiple tracer populations help break degeneracies in bias measurements.

Abstract

Multi-field models of inflation predict an inequality between the amplitude tauNL of the collapsed limit of the four-point correlator of the primordial curvature perturbation and the amplitude fNL of the squeezed limit of its three-point correlator. While a convincing detection of non-Gaussianity through the squeezed limit of the three-point correlator would rule out all single-field models, a robust confirmation or disproval of the inequality between tauNL and fNL would provide crucial information about the validity of multi-field models of inflation. In this paper, we discuss to which extent future measurements of the scale-dependence of galaxy bias can test multi-field inflationary scenarios. The strong degeneracy between the effect of a non-vanishing fNL and tauNL on halo bias can be broken by considering multiple tracer populations of the same surveyed volume. If halos down to 1e13 Msun/h are resolved in a survey of volume 25(Gpc/h)^3, then testing multi-field models of inflation at the 3-\sigma level would require, for instance, a detection of tauNL at the level of tauNL~1e5 given a measurement of a local bispectrum with amplitude fNL~10. However, we find that disproving multi-field models of inflation with measurements of the non-Gaussian bias only will be very challenging, unless |fNL| > 80 and one can achieve a halo mass resolution of 1e10 Msun/h.