Faculty Publications
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Item Thermodynamic Geometry of Regular Black Hole Surrounded by Quintessence(Springer Science and Business Media Deutschland GmbH, 2021) Ahmed Rizwan, C.L.; Naveena Kumara, A.; Vaid, D.We investigate thermodynamics of regular Bardeen AdS black hole surrounded by quintessence. Pressure-Volume (P-V) and temperature-entropy (T-S) plots are obtained from the first law of black hole thermodynamics, shows a critical behaviour. This is reflected in the divergence of specific heat against entropy plots. Using the thermodynamic geometry, we have tried to affirm this critical property. From the Ruppeiner and Weinhold geometries, we have calculated the thermodynamic curvature scalar RR and RW in the quintessence dark energy regime. It is found that in our case these thermodynamic scalars can only identify the critical behaviour and fail to show divergence at the phase transition points observed in specific heat study. © 2021, Springer Nature Singapore Pte Ltd.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 Effect of dark energy in geometrothermodynamics and phase transitions of regular Bardeen AdS black hole(Springer, 2019) Ahmed Rizwan, C.L.; Naveena Kumara, A.; Rajani, K.V.; Vaid, D.; Ajith, K.M.We study the thermodynamics and geometrothermodynamics of regular Bardeen-AdS black hole with quintessence. The thermodynamics of the black hole is scrutinised using Temperature–Entropy (T–S), Pressure–Volume (P–v) and Gibbs energy plots, which indicates a critical behaviour. The behaviour is also confirmed from the divergence of specific heat against entropy, which shows a second-order phase transition. Furthermore, we observe that the quintessence state parameter ? shifts the transition point to lower entropy values. Using the concept of thermodynamic Ruppeiner and Weinhold geometry, we calculated the thermodynamic curvature scalar RR and RW in the quintessence dark energy regime (?= - 2 / 3 ). While these curvature scalars enable us to identify the critical behaviour, they do not show divergence at the phase transition points observed in specific heat study. To resolve this puzzle, we have adopted the method of geometrothermodynamics proposed by Hernando Quevedo. Choosing a Legendre invariant ‘Quevedo’ metric, the curvature scalar RQ shows singularity at the same point as seen in the specific heat divergence. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Item Ruppeiner geometry, reentrant phase transition, and microstructure of Born-Infeld AdS black hole(American Physical Society, 2021) Naveena Kumara, A.; Ahmed Rizwan, C.L.; Hegde, K.; Ajith, K.M.; Ali, M.S.Born-Infeld AdS black hole exhibits a reentrant phase transition for certain values of the Born-Infeld parameter b. This behavior is an additional feature compared to the van der Waals like phase transition observed in charged AdS black holes. Therefore, it is worth observing the underlying microscopic origin of this reentrant phase transition. Depending on the value of the parameter b, the black hole system has four different cases: no phase transition, a reentrant phase transition with two scenarios, or a van der Waals-like (standard) phase transition. In this article, by employing a novel Ruppeiner geometry method in the parameter space of temperature and volume, we investigate the microstructure of Born-Infeld AdS black hole via the phase transition study, which includes standard and reentrant phase transitions. We find that the microstructures of the black hole that lead to standard and reentrant phase transitions are distinct in nature. The standard phase transition is characterized by the typical RN-AdS microstructure. In this case, the small black hole phase has a dominant repulsive interaction for the low temperature case. Interestingly, during the reentrant phase transition, displayed by the system in a range of pressures for specific b values, the dominant attractive nature of interaction in the microstructure is preserved. Our results suggest that in the reentrant phase transition case, the intermediate black holes behave like a bosonic gas, and in the standard phase transition case the small black holes behave like a quantum anyon gas. In both cases, the large black hole phase displays an interaction similar to the bosonic gas. The critical phenomenon is observed from the curvature scalar, including the signature of the reentrant phase transition. © 2021 American Physical Society.Item Rotating black hole with an anisotropic matter field as a particle accelerator(IOP Publishing Ltd, 2021) Ahmed Rizwan, C.L.; Naveena Kumara, A.; Hegde, K.; Ali, M.S.; Ajith, K.M.Recently, a generalised solution for Einstein equations for a rotating black hole, surrounded by matter field was proposed, which is the Kerr-Newman spacetime with an anisotropic matter [Phys. Rev. D. 101 064067]. Due to the negative radial pressure of the anisotropic matter, the solution possesses an additional hair along with the conventional mass, charge and spin. In this article we show that, this new class of black holes can act as a cosmic particle accelerator during the collision of two generic particles in its gravitational field in the ergo-region. The centre of mass energy of the particles shoots to an arbitrary high value in the vicinity of the event horizon for the extremal black hole. The physical conditions for the collision to take place are obtained by studying the horizon structure and circular particle motion. The results obtained are interesting from an astrophysical perspective. © 2021 IOP Publishing Ltd.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 and continuous phase transition of a regular Hayward black hole in anti-de Sitter spacetime(Physical Society of Japan, 2021) Naveena Kumara, A.; Ahmed Rizwan, C.L.; Hegde, K.; Ali, M.S.; Ajith, K.M.In this article we study the thermodynamic phase transition of a regular Hayward-AdS black hole, by introducing a new order parameter, which is the potential conjugate to the magnetic charge arising from a non-linearly coupled electromagnetic field. We use Landau continuous phase transition theory to discuss the van der Waals-like critical phenomena of the black hole. The well-known interpretation of the phase transition of an AdS black hole as being a large and small black hole transition is re-interpreted as being a transition between a high-potential phase and a low-potential phase. The microstructure associated with this phase transition is studied using the Ruppeiner geometry. By investigating the behaviour of the Ruppeiner scalar curvature, we find that charged and uncharged (effective) molecules of the black hole have distinct microstructure, which is analogous to that of fermion and boson gas. © 2021 The Author(s) 2021. Published by Oxford University Press on behalf of the Physical Society of Japan.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.