arXiv subjects

Chandrasekhar Bhamidipati

Publications and source records attributed to Chandrasekhar Bhamidipati.

At least 37 records · Page 2Linked to original sources

arXiv2021

Contact geometry and quantum thermodynamics of nanoscale steady states

We develop a geometric formalism suited for describing the quantum thermodynamics of a certain class of nanoscale systems (whose density matrix is expressible in the McLennan--Zubarev form) at any arbitrary non-equilibrium steady state. It is shown that the non-equilibrium steady states are points on control parameter spaces which are in a sense generated by the steady state Massieu--Planck function. By suitably altering the system's boundary conditions, it is possible to take the system from one steady state to another. We provide a contact Hamiltonian description of such transformations and show that moving along the geodesics of the friction tensor results in a minimum increase of the free entropy along the transformation. The control parameter space is shown to be equipped with a natural Riemannian metric that is compatible with the contact structure of the quantum thermodynamic phase space which when expressed in a local coordinate chart, coincides with the Schlögl metric. Finally, we show that this metric is conformally related to other thermodynamic Hessian metrics which might be written on control parameter spaces. This provides various alternate ways of computing the Schlögl metric which is known to be equivalent to the Fisher information matrix.

cond-mat.stat-mech↗

arXiv2021

Novel relations in massive gravity at Hawking-Page transition

Sign and magnitude of Ruppeiner's curvature $R_N$ is an empirical indicator of the respective nature and strength of microstructures of a thermodynamic system. For d-dimensional Schwarzschild black holes in AdS, $R_N$ at the Hawking-Page (HP) transition point is a universal constant. In this article we study the nature of $R_N$ at HP transition in a massive gravity theory and show that its constancy is broken due to the dependence on graviton mass as well as horizon topology. Although, when the graviton mass reaches a critical value the HP transition is driven to zero temperature, and $R_N$ at this point again approaches a universal negative constant, independent of all parameters of the theory. The geometry of black holes in AdS close to the HP transition point is also studied via novel near horizon scaling limits, and reveals the emergence of fully decoupled Rindler spacetimes.

gr-qc↗

arXiv2021

Ruppeiner curvature along a renormalization group flow

We report on an investigation of Ruppeiner curvature $R_U$ for $(d+1)$-dimensional hyperbolic black holes in anti-de Sitter spacetimes and its connection with Renormalization Group (RG) flows in the dual d-dimensional conformal field theories (CFTs) in Minkowski spacetimes. A repulsive type interaction among microstructures is found, which is weaker for positive mass black holes and grows stronger for negative mass black holes at low temperatures. In particular, we show that $R_U$ evaluated along a zero mass curve is a universal constant, depending only on the dimension of space-time. The extremal black holes are pointed out to have a positive Ruppeiner curvature irrespective of their horizon topology.

hep-th↗

arXiv2021

Thermodynamic curvature of AdS black holes with dark energy

In this paper, we study the effect of dark energy on the extended thermodynamic structure and interacting microstructures of black holes in AdS, through an analysis of thermodynamic geometry. Considering various limiting cases of the novel equation of state obtained in charged rotating black holes with quintessence, and taking enthalpy $H$ as the key potential in the extended phase space, we scrutinize the behavior of the Ruppeiner curvature scalar $R$ in the entropy-pressure $(S,P)$-plane (or equivalently in the temperature-volume ($T,V$)-plane). Analysis of $R$ empirically reveals that dark energy parameterized by $α$, significantly alters the dominant interactions of neutral, charged and slowly rotating black hole microstructures. In the Schwarzschild-AdS case: black holes smaller than a certain size continue to have attractive interactions whereas larger black holes are completely dominated by repulsive interactions which arise to due dark energy. For charged or rotating AdS black holes with quintessence, $R$ can change sign at multiple points depending upon the relation between $α$ and charge $q$ or angular momentum $J$. In particular, above a threshold value of $α$, $R$ is never negative at all, suggesting heuristically that the repulsive interactions due to quintessence are long ranged as opposed to the previously known short ranged repulsion in charged AdS black holes. A mean field interaction potential is proposed whose extrema effectively capture the points where the curvature $R$ changes sign.

gr-qc↗

arXiv2020

Thermodynamic curvature of the Schwarzschild-AdS black hole and Bose condensation

In the AdS/CFT correspondence, a dynamical cosmological constant $Λ$ in the bulk corresponds to varying the number of colors $N$ in the boundary gauge theory with a chemical potential $μ$ as its thermodynamic conjugate. In this work, within the context of Schwarzschild black holes in $AdS_5 \times S^5$ and its dual finite temperature $\mathcal{N}=4$ superconformal Yang-Mills theory at large $N$, we investigate thermodynamic geometry through the behavior of the Ruppeiner scalar $R$. The sign of $R$ is an empirical indicator of the nature of microscopic interactions and is found to be negative for the large black hole branch implying that its thermodynamic characteristics bear qualitative similarities with that of an attraction dominated system, such as an ideal gas of bosons. We find that as the system's fugacity approaches unity, $R$ takes increasingly negative values signifying long range correlations and strong quantum fluctuations signaling the onset of Bose condensation. On the other hand, $R$ for the small black hole branch is negative at low temperatures and positive at high temperatures with a second order critical point which roughly separates the two regions.

hep-th↗

arXiv2020

Critical Heat Engines in Massive Gravity

With in the extended thermodynamics, we study the efficiency $η_k$ of critical heat engines for charged black holes in massive gravity for spherical ($k=1$), flat ($k=0$) and hyperbolic ($k=-1$) topologies. Although, $η_k$ is in general higher (lower) for hyperbolic (spherical) topology, we show that this order can be reversed in critical heat engines with efficiency higher for spherical topology, following in particular the order: $ η_{\rm -1}^{\phantom{-1}} < η_{\rm 0}^{\phantom{0}} < η_{\rm +1}^{\phantom{+1}}$. Furthermore, the study of the near horizon region of the critical hole shows that, apart from the known $q\rightarrow \infty $ condition, additional scalings of massive gravity parameters, based on the topology of the geometry are required, to reveal the presence of a fully decoupled Rindler space-time with vanishing cosmological constant.

hep-th↗

arXiv2020

Ruppeiner Geometry, Phase Transitions and Microstructures of Black Holes in Massive Gravity

Using the new normalized thermodynamic scalar curvature, we investigate the microstructures and phase transitions of black holes in massive gravity for horizons of various topologies. We find that the graviton mass enhances the repulsive interactions of small black holes and weakens the attractive interactions of large black holes, with possiblity of new repulsive regions for microstructures in phase space. In addition, the repulsive interactions of small black hole are strong for spherical topology, followed by flat and hyperbolic topology; while, the attractive interactions of large black hole are strong for hyperbolic topology, followed by flat and weakest for spherical topology.

hep-th↗

arXiv2020

Thermodynamic geometry for charged Gauss-Bonnet black holes in AdS spacetimes

In this paper, we study the thermodynamic geometry of charged Gauss-Bonnet black holes (and Reissner-Nordström black holes, for the sake of comparison) in AdS: in both $(T,V)$- and $(S,P)$-planes. The thermodynamic phase space is known to have an underlying contact and metric structure; Ruppeiner geometry then naturally arises in this framework. Sign of Ruppeiner curvature can be used to probe the nature of interactions between the black hole microstructures. It is found that there are both attraction and repulsion dominated regions which are in general determined by the electric charge, Gauss-Bonnet coupling and horizon radius of the black hole. The results are physically explained by considering that these black hole systems consist of charged as well as neutral microstructures much like a binary mixture of fluids.

gr-qc↗

arXiv2020

Thermodynamic geometry and interacting microstructures of BTZ black holes

In this work, we present a study to probe the nature of interactions between black hole microstructures for the case of the BTZ black holes. Even though BTZ black holes without any angular momentum or electric charge thermodynamically behave as an ideal gas, i.e. with non-interacting microstructures; in the presence of electric charge or angular momentum, BTZ black holes are associated with repulsive interactions among the microstructures. We extend the study to the case of exotic BTZ black holes with mass $M = αm + γ\frac{j}{l}$ and angular momentum $J=αj + γl m$, for arbitrary values of $ (α, γ)$ ranging from purely exotic $(α=0,γ=1)$, slightly exotic $(α> \frac{1}{2},γ< \frac{1}{2})$ and highly exotic $(α< \frac{1}{2}, γ> \frac{1}{2})$. We find that unlike the normal BTZ black holes (the case $α=1,γ=0$), there exist both attraction as well as repulsion dominated regions in all the cases of exotic BTZ black holes.

hep-th↗

arXiv2019

Contact geometry and thermodynamics of black holes in AdS spacetimes

In this paper we discuss a formulation of extended phase space thermodynamics of black holes in Anti de Sitter (AdS) spacetimes from the contact geometry point of view. Thermodynamics of black holes can be understood within the framework of contact geometry as flows of vector fields generated by Hamiltonian functions on equilibrium submanifolds in the extended phase space that naturally incorporates the structure of a contact manifold. Deformations induced by the contact vector fields are used to construct various maps among thermodynamic quantities. Thermodynamic variables and equations of state of Schwarzschild black holes are mapped to that of Reissner-Nordström black holes in AdS, with charge as the deformation parameter. In addition, the equations of state of general black holes in AdS are shown to emerge from the high-temperature ideal gas limit equations via suitable deformations induced by contact vector fields. The Hamilton-Jacobi formalism analogous to mechanics is set up, and the corresponding characteristic curves of contact vector fields are explicitly obtained to model thermodynamic processes of black holes. Extension to thermodynamic cycles in this framework is also discussed.

hep-th↗

arXiv2019

Action-angle variables for the purely nonlinear oscillator

In this letter, we study the purely nonlinear oscillator by the method of action-angle variables of Hamiltonian systems. The frequency of the non-isochronous system is obtained, which agrees well with the previously known result. Exact analytic solutions of the system involving generalized trigonometric functions are presented. We also present arguments to show the adiabatic invariance of the action variable for a time-dependent purely nonlinear oscillator.

physics.class-ph↗

arXiv2019

Chaos in Charged Gauss-Bonnet AdS Black Holes in Extended Phase Space

We study the onset of chaos due to temporal and spatially periodic perturbations in charged Gauss-Bonnet AdS black holes in extended thermodynamic phase space, by analyzing the zeros of the appropriate Melnikov functions. Temporal perturbations coming from a thermal quench in the unstable spinodal region of P-V diagram, may lead to chaos, when a certain perturbation parameter $γ$ saturates a critical value, involving the Gauss-Bonnet coupling $α$ and the black hole charge $Q$. A general condition following from the equation of state is found, which can rule out the existence of chaos in any black hole. Using this condition, we find that the presence of charge is necessary for chaos under temporal perturbations. In particular, chaos is absent in neutral Gauss-Bonnet and Lovelock black holes in general dimensions. Chaotic behavior continues to exist under spatial perturbations, irrespective of whether the black hole carries charge or not.

hep-th↗

arXiv2019

A Note on Circular Geodesics and Phase Transitions of Black Holes

The circular motion of charged test particles in the gravitational field of a Reissner-Nordström black hole in Anti de Sitter space-time is investigated, using a set of independent parameters, such as charge Q, mass M and cosmological constant $Λ= -3/l^2$ of the space-time, and charge to mass ratio $ε=q/m$ of the test particles. Classification of different spatial regions where circular motion is allowed, is presented, showing in particular, the presence of orbits at special limiting values, $M=4/\sqrt{6} Q$ and $l=6 Q$. Thermodynamically, these values are known to occur when the black hole is on the verge of a second order phase transition, there by, giving an interesting connection between thermodynamics and geodesics of black holes. We also comment on the possibility of such a connection for black holes in flat spacetime in a box.

hep-th↗

arXiv2018

A Note on Critical Nonlinearly Charged Black Holes

Within the extended phase space thermodynamics, we study aspects of power Yang-Mills and power Maxwell black holes at criticality, as the corresponding non-linearity power parameters $γ$ and $s$ are varied. On comparison, the approach of efficiency of heat engines to Carnot limit in both the systems is shown to coincide when $γ=s=1$. For $γ=s> (<) 1$, Maxwell (Yang-Mills) system dominates over Yang-Mills (Maxwell). The motion of charged particles in the critical Power Yang-Mills system is then investigated, together with a study of variation of critical mass to charge ratios with the power $γ$.

hep-th↗

arXiv2017

Heat Engines for Dilatonic Born-Infeld Black Holes

In the context of dilaton coupled Einstein gravity with a negative cosmological constant and a Born-Infeld field, we study heat engines where charged black hole is the working substance. Using the existence of a notion of thermodynamic mass and volume (which depend on the dilaton coupling), the mechanical work takes place via the pdV terms present in the first law of extended gravitational thermodynamics. Efficiency is analyzed as a function of dilaton and Born-Infeld couplings, and results are compared with analogous computations in the related conformal solutions in the Brans-Dicke Born-Infeld theory and black holes in Anti de Sitter space-time.

hep-th↗

arXiv2017

A Note on Gauss-Bonnet Black Holes at Criticality

With in the extended thermodynamics, we give a comparative study of critical heat engines for Gauss-Bonnet and charged black holes in AdS in five dimensions, in the limit of large Gauss-Bonnet parameter $α$ and charge $q$, respectively. We show that the approach of efficiency of heat engines to Carnot limit in Gauss-Bonnet black holes is higher(lower) than charged black holes when corresponding parameters are small(large).

hep-th↗

arXiv2015

Heisenberg Symmetry and Collective Modes of One Dimensional Unitary Correlated Fermions

The correlated fermionic many-particle system, near infinite scattering length, reveals an underlying Heisenberg symmetry in one dimension, as compared to an $SO(2,1)$ symmetry in two dimensions. This facilitates an exact map from the interacting to the non-interacting system, both with and without a harmonic trap, and explains the short-distance scaling behavior of the wave-function. Taking advantage of the phenomenological Calogero-Sutherland-type interaction, motivated by the density functional approach, we connect the ground-state energy shift, to many-body correlation effect. For the excited states, modes at integral values of the harmonic frequency $ω$, are predicted in one dimension, in contrast to the breathing modes with frequency $2ω$ in two dimensions.

cond-mat.quant-gas↗

arXiv2015

Beta-gamma system, pure spinors and Hilbert series of arc spaces

Algorithms are presented for calculating the partition function of constrained beta-gamma systems in terms of the generating functions of the individual fields of the theory, the latter obtained as the Hilbert series of the arc space of the algebraic variety defined by the constraint. Examples of a beta-gamma system on a complex surface with an $A_1$ singularity and pure spinors are worked out and compared with existing results.

hep-th↗