Frame Representation of the First-Order Part of the Laplace-Beltrami Operator

Abstract

We investigate the geometric content of the first-order part of the Laplace--Beltrami operator on an oriented Riemannian manifold. Relative to an arbitrary local orthonormal frame, the first-order part of the Laplace--Beltrami operator defines a distinguished vector field, whose coefficients are expressed through the Levi--Civita connection forms. The corresponding one-form determines a covariant derivative whose connection factorization removes the first-order part of the Laplace--Beltrami operator and replaces it by a natural scalar potential. The construction is frame dependent. We show that its transformation under local rotations of the orthonormal frame compensates the corresponding variation of the sum-of-squares part, leaving the full Laplace--Beltrami operator invariant. These results reveal the geometric role of the first-order part of the Laplace--Beltrami operator.