D'Atri spaces and the total scalar curvature of hemispheres, tubes and cylinders

TL;DR

This paper characterizes 3-dimensional D'Atri spaces via total scalar curvature of geodesic hemispheres and explores conditions under which manifold properties are determined by curvature of tubes and cylinders.

Contribution

It establishes a characterization of D'Atri spaces in three dimensions using total scalar curvature, contrasting with higher-dimensional cases, and addresses a question by Gheysens and Vanhecke.

Findings

3D D'Atri spaces characterized by scalar curvature of hemispheres

Total scalar curvature condition for cylinders implies D'Atri in bounded curvature spaces

Negative answer to Gheysens and Vanhecke's question

Abstract

B. Csik\'os and M. Horv\'ath proved that if a connected Riemannian manifold of dimension at least $4$ is harmonic, then the total scalar curvatures of tubes of small radius about a regular curve depend only on the length of the curve and the radius of the tube, and conversely, if the latter condition holds for cylinders, i.e., for tubes about geodesic segments, then the manifold is harmonic. In the present paper, we show that in contrast to the higher dimensional case, a connected 3-dimensional Riemannian manifold has the above mentioned property of tubes if and only if the manifold is a D'Atri space, furthermore, if the space has bounded sectional curvature, then it is enough to require the total scalar curvature condition just for cylinders to imply that the space is D'Atri. This result gives a negative answer to a question posed by L. Gheysens and L. Vanhecke. To prove these statements, we give a characterization of D'Atri spaces in terms of the total scalar curvature of geodesic hemispheres in any dimension.