New Li--Yau--Hamilton Inequalities for the Ricci Flow via the Space-time Approach

Abstract

We generalize Hamilton's matrix Li-Yau-type Harnack estimate for the Ricci flow by considering the space of all LYH (Li-Yau-Hamilton) quadratics that arise as curvature tensors of space-time connections satisfying the Ricci flow with respect to the natural space-time degenerate metric. As a special case, we employ scaling arguments to derive a linear-type matrix LYH estimate. The new LYH quadratics obtained in this way are associated to the system of the Ricci flow coupled to a 1-form and a 2-form evolving by heat-type equations. In the case of a Kaehler solution, a special case of our linear-type trace LYH estimate is weaker than but qualitatively equivalent to Hamilton's trace estimate.

This revision mostly makes changes in terminology to match the published version of the paper. In particular, we now call our estimates `Li--Yau--Hamilton inequalities'. (51 pages)