Short-time asymptotics of the regularizing effect for semigroups generated by quadratic operators

TL;DR

This paper investigates the short-time regularizing effects of semigroups generated by accretive quadratic operators with zero singular spaces, revealing directional dependence and deriving sharp subelliptic estimates with applications to hypoelliptic operators.

Contribution

It provides a detailed analysis of the short-time asymptotics of regularization for these operators, highlighting the influence of phase space directions and the structure of the singular space.

Findings

Regularizing effect depends on phase space directions.

Derived sharp subelliptic estimates for degenerate operators.

Applications to hypoelliptic Ornstein-Uhlenbeck and Fokker-Planck operators.

Abstract

We study accretive quadratic operators with zero singular spaces. These degenerate non-selfadjoint differential operators are known to be hypoelliptic and to generate contraction semigroups which are smoothing in the Schwartz space for any positive time. In this work, we study the short-time asymptotics of the regularizing effect induced by these semigroups. We show that these short-time asymptotics of the regularizing effect depend on the directions of the phase space, and that this dependence can be nicely understood through the structure of the singular space. As a byproduct of these results, we derive sharp subelliptic estimates for accretive quadratic operators with zero singular spaces pointing out that the loss of derivatives with respect to the elliptic case also depends on the phase space directions according to the structure of the singular space. Some applications of these results are then given to the study of degenerate hypoelliptic Ornstein-Uhlenbeck operators and degenerate hypoelliptic Fokker-Planck operators.