Cosmological Collider Physics
  We study the imprint of new particles on the primordial cosmological
fluctuations. New particles with masses comparable to the Hubble scale produce
a distinctive signature on the non-gaussianities. This feature arises in the
squeezed limit of the correlation functions of primordial fluctuations. It
consists of particular power law, or oscillatory, behavior that contains
information about the masses of new particles. There is an angular dependence
that gives information about the spin. We also have a relative phase that
crucially depends on the quantum mechanical nature of the fluctuations and can
be viewed as arising from the interference between two processes. While some of
these features were noted before in the context of specific inflationary
scenarios, here we give a general description emphasizing the role of
symmetries in determining the final result.
