Generalized $\Cal{L}$-geodesic and monotonicity of the generalized reduced volume in the Ricci flow

Abstract

Suppose $M$ is a complete n-dimensional manifold, $n\ge 2$, with a metric $\bar{g}_{ij}(x,t)$ that evolves by the Ricci flow $\partial_t \bar{g}_{ij}=-2\bar{R}_{ij}$ in $M\times (0,T)$. For any $0 0$, we will prove the existence of a $\Cal{L}_p$-geodesic which minimize the $\Cal{L}_p(q,\barτ)$-length between $p_0$ and $q$ for any $\barτ>0$. This result for the case $p=1/2$ is conjectured and used many times but no proof of it was given in Perelman's papers on Ricci flow. My result is new and answers in affirmative the existence of such $\Cal{L}$-geodesic minimizer for the $L_p(q,τ)$-length which is crucial to the proof of many results in Perelman's papers on Ricci flow. We also obtain many other properties of the generalized $\Cal{L}_p$-geodesic and generalized reduced volume.