Dimensional structure of thermodynamic topology in ultraspinning Kerr-AdS black holes

Abstract

In this paper, we apply the thermodynamic topology framework to ultraspinning Kerr-AdS black holes in arbitrary spacetime dimensions. By constructing the off-shell Helmholtz free energy and the associated vector field, black hole states are characterized as topological defects, and their phase structures are described through zero points, winding numbers, and asymptotic thermodynamic behavior. Analyses of the four- and five-dimensional cases highlight the differences between even- and odd-dimensional configurations, while the endpoint behavior of the inverse-temperature curve, together with representative higher-dimensional cases, supports the absence of additional topological classes or subclasses. We find that only two thermodynamic topological structures appear: the standard class $W^{1+}$ for most configurations, and the distinct subclass $\tilde{W}^{1+}$ for odd-dimensional black holes with maximal rotations. These results support a unified classification scheme valid across dimensions for ultraspinning Kerr-AdS black holes.