Probing P and CP Violations on the Cosmological Collider
  In direct analogy to the 4-body decay of a heavy scalar particle, the 4-point
correlation function of primordial fluctuations carries P and CP information.
The CP violation appears as a P-odd angular dependence in the imaginary part of
the trispectrum in momentum space. We construct a model with axion-like
couplings which leads to observably large CP-violating trispectrum for future
surveys. Furthermore, we show the importance of on-shell particle production in
observing P- and CP-violating signals. It is impossible to observe these
signals from local 4-scalar EFT operators that respect dS isometries, and thus
any such observation can rule out single-field EFT with sufficiently small
slow-roll parameters. This calculation opens a new frontier of studying P and
CP at very high energy scales.
