Renormalized Volumes with Boundary

TL;DR

This paper introduces a boundary-adapted volume expansion for manifolds with singular measures, revealing invariant quantities like Q-curvature and Willmore energy, with broad applications in geometric analysis.

Contribution

It develops a general renormalized volume expansion with regulator-independent anomalies applicable to various geometric structures.

Findings

Derived invariant Q-curvature and transgression pairs.

Recovered Branson's Q-curvature in special cases.

Provided explicit formulas for surfaces in 3-manifolds.

Abstract

We develop a general regulated volume expansion for the volume of a manifold with boundary whose measure is suitably singular along a separating hypersurface. The expansion is shown to have a regulator independent anomaly term and a renormalized volume term given by the primitive of an associated anomaly operator. These results apply to a wide range of structures. We detail applications in the setting of measures derived from a conformally singular metric. In particular, we show that the anomaly generates invariant (Q-curvature, transgression)-type pairs for hypersurfaces with boundary. For the special case of anomalies coming from the volume enclosed by a minimal hypersurface ending on the boundary of a Poincare--Einstein structure, this result recovers Branson's Q-curvature and corresponding transgression. When the singular metric solves a boundary version of the constant scalar curvature Yamabe problem, the anomaly gives generalized Willmore energy functionals for hypersurfaces with boundary. Our approach yields computational algorithms for all the above quantities, and we give explicit results for surfaces embedded in 3-manifolds.