Loop corrections and a new test of inflation
  Inflation is the leading paradigm for explaining the origin of primordial
density perturbations and the observed temperature fluctuations of the cosmic
microwave background. However many open questions remain, in particular whether
one or more scalar fields were present during inflation and how they
contributed to the primordial density perturbation. We propose a new
observational test of whether multiple fields, or only one (not necessarily the
inflaton) generated the perturbations. We show that our test, relating the
bispectrum and trispectrum, is protected against loop corrections at all
orders, unlike previous relations.
