Ioannis Soranidis - Kinematic, energetic, and thermodynamic properties of regular black holes

Abstract: Regular black holes have become a popular alternative to the singular mathematical black holes predicted by general relativity as they circumvent mathematical pathologies associated with the singularity while preserving crucial black hole features such as the trapping of light. Here, we will analyze how to generate these geometries and study their thermodynamic properties within the framework of general relativity. Our study reveals that the regularization of the singularity, through the introduction of a minimal length scale, has a plethora of implications, one of which is the absence of the Hawking-Page phase transition. We extend our study to the dynamical case, showing that the internal energy in the first law of black hole thermodynamics is captured by the Misner-Sharp mass and demonstrating that the linear coefficient of the Misner-Sharp mass expansion near the outer apparent horizon suffices for a complete thermodynamic description. Additionally, we analyze the behavior of the null energy condition and find that it is violated in the vicinity of the outer horizon and satisfied in the vicinity of the inner horizon, which implies that the trapped spacetime region (as determined from the behavior of null geodesic congruences) is effectively separated into an NEC-violating and an NEC-non-violating domain. Moreover, we show that massive observers and particles can cross the inner and outer horizon on an ingoing geodesic, and thus entering and exiting the supposedly trapped spacetime region is possible. Lastly, we comment on the connection between the singularity regularization and the entanglement entropy of massless scalar fields living on the regular black hole background.
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3C-QFS, 25 June 2024