Ultracontractivity and Gaussian bounds for evolution families associated with non-autonomous forms

Abstract

We develop a variational approach in order to study the qualitative properties of non-autonomous parabolic equations. Based on the method of product integrals, we discuss long-time behavior, invariance properties, and ultracontractivity of evolution families in Hilbert space. Our main results give sufficient conditions for the heat kernel of the evolution family to satisfy Gaussian-type bounds. Along the way, we study examples of non-autonomous equations on graphs, metric graphs, and domains.