The four-point correlation function of graviton during inflation
  We expand the Einstein-Hilbert action with a positive cosmological constant
up to the fourth order in terms of gravity fluctuations, and then use the in-in
formalism to calculate the four-point correlation function for gravitational
waves, including both contact and exchange diagrams, generated during a period
of exactly de Sitter expansion. In addition, we also present the general
properties of the $n$-point function of graviton in terms of both circularly
and linearly polarized states.
