A notion of the weighted $\sigma_k$-curvature for manifolds with density

TL;DR

This paper introduces a new notion of weighted $\sigma_k$-curvature for manifolds with density, extending conformal geometry concepts to measure changes, and characterizes key geometric structures using this curvature.

Contribution

It defines the weighted $\sigma_k$-curvature, proves its variational properties, and characterizes special measures like shrinking Gaussians in this framework.

Findings

Shrinking gradient Ricci solitons are local extrema of the total weighted $\sigma_k$-curvature.

Shrinking Gaussians are characterized by the total weighted $\sigma_k$-curvature functional.

Conditions for the weighted $\sigma_k$-curvature to be variational are established.

Abstract

We propose a natural definition of the weighted $\sigma_k$-curvature for a manifold with density; i.e.\ a triple $(M^n,g,e^{-\phi}\mathrm{dvol})$. This definition is intended to capture the key properties of the $\sigma_k$-curvatures in conformal geometry with the role of pointwise conformal changes of the metric replaced by pointwise changes of the measure. We justify our definition through three main results. First, we show that shrinking gradient Ricci solitons are local extrema of the total weighted $\sigma_k$-curvature functionals when the weighted $\sigma_k$-curvature is variational. Second, we characterize the shrinking Gaussians as measures on Euclidean space in terms of the total weighted $\sigma_k$-curvature functionals. Third, we characterize when the weighted $\sigma_k$-curvature is variational. These results are all analogues of their conformal counterparts, and in the case $k=1$ recover some of the well-known properties of Perelman's $\mathcal{W}$-functional.