Stability and topological nature of charged Gauss-Bonnet AdS black holes in five dimensions

We investigate the thermodynamics of Reissner-Nordström Gauss-Bonnet (RN-GB) black holes in anti–de Sitter (AdS) space with three horizon geometries (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>k</a:mi><a:mo>=</a:mo><a:mo>+</a:mo><a:mn>1</a:mn><a:mo>,</a:mo><a:mn>0</a:mn><a:mo>,</a:mo><a:mo>−</a:mo><a:mn>1</a:mn></a:math>) within the grand canonical ensemble. Using the recently developed topological approach to black hole thermodynamics, inspired by Duan’s <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>ϕ</c:mi></c:math>-mapping theory, we analyze the black holes by treating both critical points in the phase diagram and black hole solutions as defects in the thermodynamic parameter space. Our results show that the Gauss-Bonnet coupling significantly alters the topological classification of RN-GB AdS black holes, distinguishing them from their RN AdS counterparts in the grand canonical ensemble while aligning with their canonical ensemble counterparts. Complementary analyses of local stability using specific heat validate the implication of topological analysis. Furthermore, an evaluation of global stability via Gibbs free energy provides a comprehensive understanding on system phase structure. Notably, for <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>k</e:mi><e:mo>=</e:mo><e:mo>+</e:mo><e:mn>1</e:mn></e:math>, topological analysis suggests liquid-gas-type phase transitions, whereas global analysis favors Hawking-Page transitions. For <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>k</g:mi><g:mo>=</g:mo><g:mo>−</g:mo><g:mn>1</g:mn></g:math>, topology indicates a single stable black hole branch, yet the global analysis reveals the presence of Hawking-Page transitions.

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