Brouwer Degree of Thermodynamic Multicritical Points in Black Holes

Abstract

In this manuscript, we propose a novel topological framework based on the heat capacity of black holes to investigate the topology of thermodynamic multicritical points. We construct a two-dimensional thermodynamic vector field whose isolated zeros correspond to the critical points of the system. The local topology of each critical point is characterized by its Brouwer degree, which serves as a locally conserved topological quantity. Applying this formalism to several AdS black hole solutions, we demonstrate that each system possesses a globally conserved topological charge. Although the number of thermodynamic critical points changes as the thermodynamic parameters are varied, the total topological charge remains invariant throughout the evolution. We show that these topological transitions are governed by the creation or annihilation of topologically neutral defect pairs carrying opposite Brouwer degrees. Our results provide a unified topological framework for understanding the emergence, evolution, and classification of thermodynamic multicritical points in black hole systems.