Testing multifield inflation with halo bias

Multifield models of inflation predict an inequality between the amplitude τ NL 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 singlefield models, a robust confirmation or disproval of the inequality between τ _NL and f_NL would provide crucial information about the validity of multifield models of inflation. In this paper, we discuss to which extent future measurements of the scale dependence of halo bias can test multifield inflationary scenarios. The strong degeneracy between the effect of a non-vanishing f_NL and τ _NL on halo bias can be broken by considering multiple tracer populations of the same surveyed volume. If haloes down to 10¹³M⊙ h^-1 are resolved in a survey of volume 25 (Gpc³ h^-3), then testing multifield models of inflation at the 3s level would require, for instance, a detection of τ NL at the level of τ _NL ~10⁵ given a measurement of a local bispectrum with amplitude f_NL ~ 10. However, we find that disproving multifield models of inflation with measurements of the non-Gaussian bias only will be very challenging, unless |f_NL| > 80 and one can achieve a halo mass resolution of ~10¹⁰M⊙ h^-1.