Browsing by Author "Vaid, D."

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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.
Coherent states and particle scattering in loop quantum gravity
(Springer Science and Business Media Deutschland GmbH, 2022) Vaid, D.; Suresh, D.
Quantum field theory provides us with the means to calculate scattering amplitudes. In recent years a dramatic new development has lead to great simplification of such calculations. This is based on the discovery of the “amplituhedron” in the context of scattering of massless gauge bosons in Yang–Mills theory. One of the main challenges facing Loop Quantum Gravity is the lack of a clear description of particle scattering processes and a connection to flat space QFT. Here we show a correspondence between the space of kinematic data of the scattering N massless particles and U(N) coherent states in LQG. This correspondence allows us to provide the outlines of a theory of quantum gravity based upon the dynamics of excitations living on the the positive Grassmannian. © 2022, The Author(s).
Comparative Study of Bulk and Surface Pressure of Charged AdS Black Hole
(Springer Science and Business Media Deutschland GmbH, 2021) Rajani, K.V.; Vaid, D.
One of the mostÂ interesting areas of research is the study of thermodynamic properties of black holes. In the extended phase, cosmological constant has been identified with the thermodynamic pressure of the black hole and phase transitions similar to Van der waals fluid is observed. On other side, fluid gravity correspondence which gives the connection between fluid on a d dimensional boundary and gravity theory in d + 1-dimensional bulk relates Einsteinâ€™s equations in the bulk with Navier-Stokes equations on the boundary. Projecting Einsteins equation onto a black hole horizon gives Damours Navier-Stokes equation and fluid pressure is found to be Îº8Ï€. In our present work, we are comparing the thermodynamic quantities in the bulk and boundary of charged AdS black holes. Â© 2021, Springer Nature Singapore Pte Ltd.
Connecting Loop Quantum Gravity and String Theory via Quantum Geometry
(Springer Science and Business Media Deutschland GmbH, 2021) Vaid, D.
We argue that String Theory and Loop Quantum Gravity canÂ be thought of as describing different regimes of a single unified theory of quantum gravity. LQG can be thought of as providing the pre-geometric exoskeleton out of which macroscopic geometry emerges and String Theory then becomes the effective theory which describes the dynamics of that exoskeleton. The core of the argument rests on the claim that the Nambu-Goto action of String Theory can be viewed as the expectation value of the LQG area operator evaluated on the string worldsheet. A concrete result is that the string tension of String Theory and the Barbero-Immirzi parameter of LQG turn out to be proportional to each other. Â© 2021, Springer Nature Singapore Pte Ltd.
Dynamic phase transition of black holes in massive gravity
(Academic Press Inc., 2023) Safir, T.K.; Naveena Kumara, A.N.; Punacha, S.; Ahmed Rizwan, C.L.A.; Fairoos, C.; Vaid, D.
The dynamical properties of small-large black hole phase transition in dRGT non-linear massive gravity theory are studied based on the underlying free energy landscape. The free energy landscape is constructed by specifying the Gibbs free energy to every state, and the free energy profile is used to study the different black hole phases. The small-large black hole states are characterized by probability distribution functions and the kinetics of phase transition are described by the Fokker–Planck equation. Further, a detailed study of the first passage process is presented which describes the dynamics of phase transitions. Finally, we have investigated the effect of mass and topology on the dynamical properties of phase transitions of black holes in dRGT non-linear massive gravity theory. © 2023 Elsevier Inc.
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.
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.
LQG for the bewildered: The self-dual approach revisited
(Springer International Publishing, 2016) Vaid, D.; Bilson-Thompson, S.
This primer offers a concise introduction to Loop Quantum Gravity (LQG) - a theoretical framework for uniting Quantum Mechanics (QM) with General Relativity (GR). The emphasis is on the physical aspects of the framework and its historical development in terms of self-dual variables, still most suited for a first, pedagogical encounter with LQG. The text starts by reviewing GR and the very basics of Quantum Field Theory (QFT), and then explains in a concise and clear manner the steps leading from the Einstein-Hilbert action for gravity to the construction of the quantum states of geometry, known as spin-networks, and which provide the basis for the kinematical Hilbert space of quantum general relativity. Along the way the various associated concepts of tetrads, spin-connection and holonomies are introduced. Having thus provided a minimal introduction to the LQG framework, some applications to the problems of black hole entropy and of quantum cosmology are briefly surveyed. Last but not least, a list of the most common criticisms of LQG is presented, which are then tackled one by one in order to convince the reader of the physical viability of the theory. A set of appendices provides accessible introductions to several key notions such as the Peter-Weyl theorem, duality of differential forms and Regge calculus, among others. The presentation is aimed at graduate students and researchers who have some familiarity with the tools of QM and GR, but are intimidated by the technicalities required to browse through the existing LQG literature. This primer aims at making the formalism appear a little less bewildering to the uninitiated and helps lower the barrier for entry into the field. Â© Springer International Publishing Switzerland 2017.
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.
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)
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.
Second order phase transition in thermodynamic geometry and holographic superconductivity in low-energy stringy black holes
(2018) 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).
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. Â© 2018 Author(s).
Superconducting and Antiferromagnetic Phases of Space-Time
(Hindawi Limited, 2017) Vaid, D.
A correspondence between the SO5 theory of high-TC superconductivity and antiferromagnetism, put forward by Zhang and collaborators, and a theory of gravity arising from symmetry breaking of a SO5 gauge field is presented. A physical correspondence between the order parameters of the unified SC/AF theory and the generators of the gravitational gauge connection is conjectured. A preliminary identification of regions of geometry, in solutions of Einstein's equations describing charged-rotating black holes embedded in de Sitter space-time, with SC and AF phases is carried out. © 2017 Deepak Vaid.
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 thermodynamicsÂ 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. Â© 2021, Springer Nature Singapore Pte Ltd.