Faculty Publications
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Item Criticality of charged ads black hole with a global monopole(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Naveena Kumar, A.; Ahmed Rizwan, C.L.A.; Ajith, K.M.We discuss the phase transition of charged AdS black hole surrounded by a global monopole. The cosmological constant is taken as fluid pressure and the corresponding conjugate variable as volume. In this extended phase space, the criticality is investigated from P-V isotherms, Gibbs free energy behavior and coexistence curves. The critical behavior of the Black Hole is analogous to classical van der Waals gas. This is further verified by looking at the critical exponents. The magnetic monopole parameter affects the phase structure of the black hole significantly. © Springer Nature Singapore Pte Ltd 2020.Item Effect of global monopole on the microscopic structure of rn-ads black hole(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Ahmed Rizwan, C.L.A.; Naveena Kumar, A.; Ananthram, K.S.In this work we study the microscopic structure of RN-AdS Black hole with a monopole. We utilize the connection between the thermodynamic Ruppeiner geometry and the nature of underlying microscopic interaction. The behaviour of the Ruppeiner invariant scalar is analysed in the extended space. The sign of the curvature scalar is the measure of the strength of attractive or repulsive statistical interaction. It is observed that the monopole parameter influences the microscopic structure of the black hole. © Springer Nature Singapore Pte Ltd 2020.Item The Role of Global Monopole in Joule–Thomson Effect of AdS Black Hole(Springer Science and Business Media Deutschland GmbH, 2021) Naveena Kumara, A.; Ahmed Rizwan, C.L.; Ajith, K.M.We study the throttling process of the AdS black hole with a global monopole in the extended phase space. In the approach followed, the cosmological constant and the black hole mass are identified with the thermodynamic pressure and enthalpy, respectively. We investigate the dependency of the inversion temperature and isenthalpic curves on the global monopole parameter η. Our study shows a close resemblance between the phase transition of the black hole in the extended phase space and Van der Waals fluid. The presence of global monopole plays an important role in the throttling process. © 2021, Springer Nature Singapore Pte Ltd.Item Joule-Thomson expansion in AdS black hole with a global monopole(World Scientific Publishing Co. Pte Ltd wspc@wspc.com.sg, 2018) Ahmed Rizwan, C.L.; Naveena Kumara, A.; Vaid, D.; Ajith, K.M.In this paper, we investigate the Joule-Thomson effects of AdS black holes with a global monopole. We study the effect of the global monopole parameter on the inversion temperature and isenthalpic curves. The obtained result is compared with Joule-Thomson expansion of van der Waals fluid, and the similarities were noted. Phase transition occuring in the extended phase space of this black hole is analogous to that in van der Waals gas. Our study shows that global monopole parameter plays a very important role in Joule-Thomson expansion. © 2018 World Scientific Publishing Company.Item Repulsive interactions in the microstructure of regular Hayward black hole in anti-de Sitter spacetime(Elsevier B.V., 2020) Naveena Kumara, A.N.; Ahmed Rizwan, C.L.A.; Hegde, K.; Ajith, K.M.We study the interaction between the microstructures of Hayward-AdS black hole using Ruppeiner geometry. Our investigation shows that the dominant interaction between the black hole molecules is attractive in most part of the parametric space of temperature and volume, as in van der Waals system. However, in contrast to the van der Waals fluid, there exists a weak dominant repulsive interaction for small black hole phase in some parameter range. This result clearly distinguishes the interactions in a magnetically charged black hole from that of van der Waals fluid. However, these sort of interactions are characteristic for charged black holes since they do not dependent on magnetic charge or temperature. © 2020 The Author(s)Item Coexistent physics and microstructure of the regular Bardeen black hole in anti-de Sitter spacetime(Academic Press Inc. apjcs@harcourtbrace.com, 2020) Ahmed Rizwan, C.L.A.; Naveena Kumara, A.N.; Hegde, K.; Vaid, D.We study the phase structure and the microscopic interactions of a regular Bardeen–AdS black hole. The stable and metastable phases in the black hole are analysed through coexistence and spinodal curves. The solutions are obtained numerically as the analytic solution to the coexistence curve is not feasible. The Pr?Tr coexistence equation is obtained using a fitting formula. The coexistence and spinodal curves are plotted in Pr?Tr and Tr?Vr planes to explore the phase structure of the black hole. In the second part of our study, we were able to probe the microscopic interactions of the regular Bardeen–AdS black hole using the novel Ruppeiner geometry proposed by Wei et al. (2019). It is found that the microscopic interactions are not the same in small black hole (SBH) and large black hole (LBH) phases. In the SBH phase, there exists a repulsive interaction in the microstructure in the low temperature regime. In contrast, the microstructure associated with the LBH phase has an attractive interaction throughout the parameter space. We found that, along the coexistence temperature, both the SBH and LBH branches diverge to negative infinity with a critical exponent equal to 1?2. © 2020 Elsevier Inc.Item Null geodesics and thermodynamic phase transition of four-dimensional Gauss–Bonnet AdS black hole(Academic Press Inc., 2021) Hegde, K.; Naveena Kumara, A.; Ahmed Rizwan, C.L.; Ali, M.S.; Ajith, K.M.Modified gravity theories are of great interest in both observational and theoretical studies. In this article, we study the correlation between the null geodesics and the thermodynamic phase transition of a four-dimensional Gauss–Bonnet AdS black hole. Firstly, we study the phase structure of the black hole, using the coexistence and spinodal curves, to understand the phase transition in an extended phase space. The imprints of these phase transition features can be clearly observed from the functional dependence of photon orbit radius and minimum impact parameter with respect to the Hawking temperature and pressure. The change in these two quantities during the phase transition serve as order parameters which characterise the critical behaviour. The correlation shows that thermodynamic phase transition can be studied by observing the effects of strong gravitational field on the photon orbit and vice versa. © 2021 Elsevier Inc.Item Microstructure of five-dimensional neutral Gauss–Bonnet black hole in anti-de Sitter spacetime via P- V criticality(Springer, 2023) Naveena Kumara, A.N.; Ahmed Rizwan, C.L.A.; Hegde, K.; Ali, M.S.; Ajith, K.M.In this article, we analytically investigate the microstructure of a five-dimensional neutral Gauss–Bonnet black hole, in the background of anti-de Sitter spacetime, by using the scalar curvature of the Ruppeiner geometry constructed via adiabatic compressibility. The microstructure details associated with the small-large black hole phase transition are probed in the parameter space of pressure and volume. The curvature scalar shows similar properties for both phases of the black hole, it diverges at the critical point with a critical exponent 2, and approaches zero for extremal black holes. We show that the dominant interaction among black hole molecules is attractive. This study also confirms that the nature of the microstructure interaction remains unchanged during the small-large black hole phase transition, even though the microstructures are different for both phases. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Physical process first law and the entropy change of Rindler horizons(Academic Press Inc., 2023) Safir, T.K.; Fairoos, C.; Vaid, D.The physical process version of the first law can be obtained for bifurcate Killing horizons with certain assumptions. Especially, one has to restrict to the situations where the horizon evolution is quasi-stationary, under perturbations. We revisit the analysis of this assumption considering the horizon perturbations of Rindler horizon by a spherically symmetric object. We demonstrate that even if the quasi-stationary assumption holds, the change in entropy, in four space–time dimensions, diverges when considered between asymptotic cross-sections. However, these divergences do not appear in higher dimensions. We also analyze these features in the presence of a positive cosmological constant. In the process, we prescribe a recipe to establish the physical process first law in such ill-behaved scenarios. © 2023 Elsevier Inc.Item Dynamics and kinetics of phase transition for regular AdS black holes in general relativity coupled to nonlinear electrodynamics(World Scientific, 2023) Naveena Kumara, A.N.; Punacha, S.; Hegde, K.; Ahmed Rizwan, C.L.A.; Ajith, K.M.; Ali, M.S.We study the stochastic dynamics and kinetics of the phase transition of the regular black holes in Anti-de Sitter spacetime by employing the free energy landscape. Our investigation focuses on two important classes of regular black hole solutions, namely the Hayward and Bardeen, which can be obtained from coupling of non-linear electrodynamics. The dynamics of the phase transition is described by the Fokker-Planck equation, using which, we investigate the probabilistic evolution of regular AdS black holes. We solve this equation numerically by imposing both reflecting and absorbing boundary conditions and appropriate initial conditions. In this context, the on-shell Gibbs free energy is treated as a function of the event horizon radius, where the difference of the event horizon radii in different phases serves as the order parameter for the phase transition. The study allows us to probe the dynamic process of transitioning between coexisting small and large black hole phases due to thermal fluctuations, as quantified by the calculation of the first passage time. Furthermore, we explore the influence of temperature on this dynamic process. This research contributes to a deeper understanding of the microstructures of regular AdS black holes. © 2023 World Scientific Publishing Company.