On the paper: Bruce Kleiner, John Lott, Notes on Perelman's papers, Geom. Topol. 12(5): 2587-2855 (2008). DOI: 10.2140/gt.2008.12.2587
The authors wrote the following statement:
(Here $-\Delta$ is the semi-posiitve Laplacian operator.)
It seems that on closed Riemannian manifold $(M,g)$, for any compact interval $[a,b]$, with an initial function $u(b)$, we can always solve the backward heat flow $$\frac{\partial u}{\partial t}=-\Delta u+Ru,$$ where $R$ is a smooth function.
Q Can anyone give a reference about the existence (uniqueness) about the above backward heat flow?
Thanks in advance