Convexity Properties of Harmonic Functions on Parameterized Families of Hypersurfaces
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OriginalversjonJournal of Geometric Analysis. 2019, 1-27. 10.1007/s12220-019-00307-y
It is known that the L2L2-norms of a harmonic function over spheres satisfy some convexity inequality strongly linked to the Almgren’s frequency function. We examine the L2L2-norms of harmonic functions over a wide class of evolving hypersurfaces. More precisely, we consider compact level sets of smooth regular functions and obtain a differential inequality for the L2L2-norms of harmonic functions over these hypersurfaces. To illustrate our result, we consider ellipses with constant eccentricity and growing tori in R3.R3. Moreover, we give a new proof of the convexity result for harmonic functions on a Riemannian manifold when integrating over spheres. The inequality we obtain for the case of positively curved Riemannian manifolds with non-constant curvature is slightly better than the one previously known.