Transport of Gaussian measures under the flow of one-dimensional fractional nonlinear Schrödinger equations

We study the transport property of Gaussian measures on Sobolev spaces of periodic functions under the dynamics of the one-dimensional cubic fractional nonlinear Schrödinger equation. For the case of second-order dispersion or greater, we establish an optimal regularity result for the quasi-invariance of these Gaussian measures, following the approach by Debussche and Tsutsumi (2021). Moreover, we obtain an explicit formula for the Radon-Nikodym derivative and, as a corollary, a formula for the two-point function arising in wave turbulence theory. We also obtain improved regularity results in the weakly dispersive case, extending those by the first author and Trenberth (2019). Our proof combines the approach introduced by Planchon, Tzvetkov and Visciglia (2020) and that of Debussche and Tsutsumi (2021).