Testing Multi-Field Inflation with Galaxy Bias
  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.
