Faculty Publications
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Item Second order phase transition in thermodynamic geometry and holographic superconductivity in low-energy stringy black holes(American Institute of Physics Inc. subs@aip.org, 2018) Ahmed Rizwan, C.L.A.; Vaid, D.We study holographic superconductivity in low-energy stringy Garfinkle-Horowitz-Strominger (GHS) dilaton black hole background. We finds that superconducting properties are much similar to s-wave superconductors. We show that the second-order phase transition indicated from thermodynamic geometry is not different from superconducting phase transition. © 2018 Author(s).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 Phase transition and thermodynamic geometry of regular Bardeen black hole in higher dimensions(American Institute of Physics Inc., 2020) Rajani, K.V.; Ahmed Rizwan, C.L.A.; Naveena Kumara, A.N.In this work we study the thermodynamic properties and phase transition of higher dimensional regular Bardeen black hole in AdS spacetime. The black hole thermodynamics is studied using Hawking temperature vs Bekenstein entropy (T - S) plot, which shows a critical behaviour. This is followed by the investigation of the phase transition by observing the divergence of specific heat. The critical behaviour of the blackhole is further analysed in detail via Ruppeiner geometry. The divergence behaviour similar to specific heat is found in Ruppeiner curvature scalar confirms a second order phase transition. © 2020 Author(s).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 Photon orbits and thermodynamic phase transition of regular AdS black holes(American Physical Society subs@aip.org;revtex@aps.org;prx@aps.org;prxtex@aps.org;help@aps.org;prb@aps.org, 2020) Naveena Kumara, A.N.; Ahmed Rizwan, C.L.A.; Punacha, S.; Ajith, K.M.; Ali, M.S.We probe the phase structure of the regular anti-de Sitter (AdS) black holes using the null geodesics. The radius of photon orbit and minimum impact parameter shows a nonmonotonous behavior below the critical values of the temperature and the pressure, corresponding to the phase transition in extended phase space. The respective differences of the radius of unstable circular orbit and the minimum impact parameter can be seen as the order parameter for the small-large black hole phase transition, with a critical exponent 1/2. Our study shows that there exists a close relationship between the gravity and thermodynamics for the regular AdS black holes. © 2020 American Physical Society.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 Regular Bardeen AdS black hole as a heat engine(Elsevier B.V., 2020) Rajani, K.V.; Ahmed Rizwan, C.L.A.; Naveena Kumara, A.N.; Vaid, D.; Ajith, K.M.We investigate the thermodynamic phase transition and heat engine efficiency in regular Bardeen AdS black hole. The thermodynamics of the black hole is analyzed in extended phase space. A first order phase transition analogous to van der Waal system is evident from this study, which is affirmed by the specific heat divergence at the critical points. A conventional heat engine is constructed by considering the black hole as working substance. The efficiency is obtained via a thermodynamic cycle in the P?V plane, which receives and ejects heat. The heat engine efficiency is improved by adding a quintessence field. The analytical expression for heat engine efficiency is derived in terms of quintessence dark energy parameter. © 2020 The Author(s)Item Rotating 4D Gauss–Bonnet black hole as a particle accelerator(Academic Press Inc., 2021) Naveena Kumara, A.; Ahmed Rizwan, C.L.A.; Hegde, K.; Ali, M.S.; Ajith, K.M.We demonstrate that the rotating four-dimensional Gauss– Bonnet black hole can act as a particle accelerator with arbitrarily high centre-of-mass (CM) energy, when collision of two general particles takes place near the event horizon. The particles are at rest initially at infinity, and by fine tuning their angular momenta within a finite range, they are released so that they follow the time-like geodesics in the black hole spacetime, and the collision taking place on the equatorial plane is observed. The Gauss–Bonnet coupling constant ?, provides a deviation in the results, from that observed in the Kerr black hole. The horizon structure, the range of allowed angular momentum and the critical angular momentum depend on the value of ?. Our results show that the CM energy depends on the coupling parameter ? in addition to the black hole spin a. For extremal cases, the CM energy diverges at the horizon, suggesting that Gauss–Bonnet black hole can also act as a particle accelerator similar to a Kerr black hole. For the non-extremal case, there exists a finite upper bound on the CM energy, the maximal value of which depends on the parameter ?. © 2021 Elsevier Inc.Item Ruppeiner geometry, P - V criticality and interacting microstructures of black holes in dRGT massive gravity(World Scientific, 2022) Safir, T.K.; Ahmed Rizwan, C.L.A.; Vaid, D.We probe the microstructure of the dRGT massive black hole in an anti-de Sitter background. The calculations are performed in an extended phase space with pressure and volume taken as fluctuation variables. We analyze the microstructure by exploiting the Ruppeiner geometry, where the thermodynamic curvature scalar is constructed via adiabatic compressibility. The nature of the curvature scalar along the coexistence line of small black hole (SBH) and large black hole (LBH) is investigated. In the microscopic interaction, we observe that the SBH phase behaves as an anyonic gas and the LBH phase is analogous to a boson gas. Further, we study the effect of graviton mass on the underlying microstructure of the black hole. © 2022 World Scientific Publishing Company.