Holographic fractional order phase transitions in CFTs dual to AdS black holes

Abstract In this work, we investigate the CFT phase transitions of various AdS black hole solutions including the Reissner–Nordström–AdS (RN-AdS) black hole, the ModMax-AdS black hole, and the RN-AdS black hole formulated within the framework of Kaniadakis statistics through the lens of the AdS/CFT correspondence. Employing the generalized Ehrenfest classification scheme based on fractional-order derivatives, we analyze the nature of phase transitions at both Davies points and critical points. Davies points, defined as the loci of divergent heat capacity, are typically associated with second-order transitions in the classical Ehrenfest paradigm. However, a refined analysis reveals that these points can be categorized into two distinct types: the first corresponds to extrema in the temperature profile, while the second aligns with its inflection point, i.e., the thermodynamic critical point. Our findings demonstrate that the order of the phase transition is sensitive to this classification, with the first type corresponding to a fractional order of 3/2, and the second to 4/3, which is the same for the RN-AdS black holes. Notably, when a specific constraint is imposed, we observe a 3/2-order phase transition for both the RN-AdS and ModMax-AdS black holes, whereas in the case of the RN-AdS black hole with Kaniadakis statistics, two critical points arise under constrained paths, each exhibiting a transition of order 4/3. This generalized, fractional-order framework enables a more precise and discriminating characterization of CFT phase transitions in holographic settings, revealing distinctions that remain hidden under traditional classifications. The results provide deeper insight into the rich structure of black hole thermodynamics on the CFT side and highlight the significance of fractional calculus as a powerful tool for probing critical phenomena within the AdS/CFT framework.