We prove quasi-invariance of Gaussian measures supported on Sobolev spaces under
the dynamics of the three-dimensional defocusing cubic nonlinear wave equation. As
in previous work on the two-dimensional case, we employ a simultaneous
renormalization on the energy functional and its time derivative. Two new ingredients
in the three-dimensional case are the construction of the weighted Gaussian
measures, based on a variational formula for the partition function inspired by
Barashkov and Gubinelli (2018), and an improved argument in controlling the
growth of the truncated weighted Gaussian measures, where we combine a
deterministic growth bound of solutions with stochastic estimates on random
distributions.
Keywords
nonlinear wave equation, Gaussian measure,
quasi-invariance, Euclidean quantum field theory