On the hypercontractivity of Ornstein-Uhlenbeck semigroups with drift
Harnack inequalities on a manifold with positive or negative Ricci curvature.
Several new Harnack estimates for positive solutions of the heat equation on a complete Riemannian manifold with Ricci curvature bounded below by a positive (or a negative) constant are established. These estimates are sharp both for small time, for large time and for large distance, and lead to new estimates for the heat kernel of a manifold with Ricci curvature bounded below.
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