Topological Conservation Laws in Magnetohydrodynamics on Higher-Dimensional Riemannian Manifolds

Abstract: Are conservation laws such as fluid enstrophy, fluid helicity, or magnetic helicity inherently tied to the geometry of Euclidean space or the dimensionality of a fluid system? In this work, we first derive the equations of ideal magnetohydrodynamics (MHD) on a general Riemannian manifold. We then demonstrate that the associated conservation laws arise not from the flatness of the metric, but rather from the intrinsic mathematical structure of the governing equations. Moreover, we demonstrate that their qualitative behavior depends crucially on whether the ambient space is of even or odd dimensions. In particular, we demonstrate that higher-dimensional magnetofluid systems admit natural generalizations of familiar topological invariants - such as fluid enstrophy, total magnetic flux, fluid helicity, cross-helicity, and magnetic helicity - under appropriate boundary and field conditions.