In this paper we prove matrix Li-Yau-Hamilton estimates for positive
solutions to the heat equation and the backward conjugate heat equation, both
coupled with the Ricci flow. We then apply such estimates to establish the
monotonicity of parabolic frequencies up to correction factors. As
applications, we obtain some unique continuation results under the
nonnegativity of sectional or complex sectional curvature.Comment: 37 pages. All comments are welcom