A Bochner formula on path space for the Ricci flow

Abstract

We generalize the classical Bochner formula for the heat flow on evolving manifolds $$(M,g_{t})_{t \in [0,T]}$$ to an infinite-dimensional Bochner formula for martingales on parabolic path space $$P{\mathcal {M}}$$ of space-time $${\mathcal {M}} = M \times [0,T]$$ . Our new Bochner formula and the inequalities that follow from it are strong enough to characterize solutions of the Ricci flow. Specifically, we obtain characterizations of the Ricci flow in terms of Bochner inequalities on parabolic path space. We also obtain gradient and Hessian estimates for martingales on parabolic path space, as well as condensed proofs of the prior characterizations of the Ricci flow from Haslhofer–Naber (J Eur Math Soc 20(5):1269–1302, 2018a). Our results are parabolic counterparts of the recent results in the elliptic setting from Haslhofer–Naber (Commun Pure Appl Math 71(6):1074–1108, 2018b).