arXiv subjects

Pankaj Chaturvedi

Publications and source records attributed to Pankaj Chaturvedi.

At least 19 recordsLinked to original sources

arXiv2026

Fractional Cosmic String Loops In Expanding Universe

We study the dynamics of circular cosmic string loops in a spatially flat Friedmann Lemaître Robertson Walker universe within a fractional Polyakov framework that incorporates nonlocal memory effects. Allowing both the loop radius and polar angle to evolve, we obtain a coupled non-autonomous system governed by string tension, cosmological expansion, and an emergent centrifugal contribution. We show that angular dynamics plays a crucial role in determining the loop evolution. In contrast to standard scenarios where loops collapse, we identify a class of solutions exhibiting sustained expansion driven by dynamically generated angular motion. The system also displays nonlinear behavior with signatures of chaos, with the onset of chaotic dynamics closely correlated with expanding solutions. Our results demonstrate that fractional memory effects and angular degrees of freedom qualitatively modify cosmic string loop dynamics, providing new mechanisms for stability in cosmological backgrounds.

hep-th↗

arXiv2024

Probe of spatial geometry from scalar induced gravitational waves

We investigate a novel probe of spatial geometry of the Universe through the observation of gravitational waves (GWs) induced by first order curvature perturbations. The existence of spatial curvature leaves imprints on the gravitational wave spectrum and formation of primordial black holes. Given the peaked scalar spectrum, the induced spectrum deviates from the flat space power spectrum and the deviation is dependent on the spatial curvature K and reheating temperature $T_{rh}$. For prolonged reheating and negative spatial curvature the spectrum is amplified enough and exhibits an additional peak solely due to K indicating a possible detection by future gravitational wave experiments including LISA and DECIGO. We also observe that the presence of negative spatial curvature improves the constraints on PBH formation, increasing the mass of black holes which are viable dark matter candidates.

astro-ph.CO↗

arXiv2024

SYK Model in a Non-Gaussian disorder ensemble and emergent Coleman's mechanism

We consider the case of the SYK model with non-gaussian disorder in the large $N$ limit. After obtaining the effective action, we derive the density of states and the free energy of the modified theory. We show that the non-gaussian disorder corresponds to a non-local Liouville theory, and non-minimally coupled 2D gravity action. It also provides a nice realization of Colemania - Coleman's idea from the 80s of generating a small Cosmological Constant. Finally, we also calculate out of time order correlation functions (OTOC) for the model.

hep-th↗

arXiv2023

Rotating black hole solutions for $f(R)$ gravity and Newman Janis Algorithm

We show that the $f(R)$-gravity theories with constant Ricci scalar in the Jordan/Einstein frame can be described by Einstein or Einstein-Maxwell gravity with a cosmological term and a modified gravitational constant. We also propose a modified Newmann-Janis algorithm to obtain the rotating axisymmetric solutions for the Einstein/Einstein-Maxwell gravity with a cosmological constant. Using the duality between the two gravity theories we show that the stationary or static solutions for the Einstein/Einstein-Maxwell gravity with a cosmological constant will also be the solutions for the dual $f(R)$-gravity with constant Ricci scalar.

gr-qc↗

arXiv2021

AdS$_3$ gravity and the complex SYK models

We provide a non conformal generalization of the Compère-Song-Strominger (CSS) boundary conditions for AdS$_3$ gravity that breaks the $\widehat u(1)$ Kac-Moody-Virasoro symmetry to two $u(1)$s. The holographic dual specified by the new boundary conditions can be understood as an irrelevant deformation of a warped conformal field theory (WCFT). Upon consistent reduction to two dimensions, AdS$_3$ gravity results in a deformed Jackiw-Teitelboim dilaton gravity model coupled to a Maxwell field. We show that near extremality the boundary conditions inherited from generalized CSS boundary conditions in three dimensions give rise to an effective action exhibiting the same symmetry breaking pattern as the complex Sachdev-Ye-Kitaev models. Besides the Schwarzian term reflecting the breaking of conformal symmetry, the effective action contains an additional term that captures the breaking of the $\widehat u(1)$ Kac-Moody symmetry.

hep-th↗

arXiv2018

A note on the complex SYK model and warped CFTs

We discuss the connections between the complex SYK model at the conformal limit and warped conformal field theories. Both theories have an $SL(2,R) \times U(1)$ global symmetry. We present comparisons on symmetries, correlation functions, the effective action and the entropy formula. We also use modular covariance to reinterpret results in the complex SYK model.

hep-th↗

arXiv2018

Holographic Quantum Entanglement Negativity

We advance a holographic conjecture for the entanglement negativity of bipartite quantum states in $(1+1)$-dimensional conformal field theories in the $AdS_3/CFT_2$ framework. Our conjecture exactly reproduces the replica technique results in the large central charge limit, for both the pure state described by the $CFT_{1+1}$ vacuum dual to bulk the pure $AdS_3$ geometry and the finite temperature mixed state dual to a Euclidean BTZ black hole respectively. The holographic entanglement negativity characterizes the distillable entanglement and reduces to a specific sum of holographic mutual informations. We briefly allude to a possible higher dimensional generalization of our conjecture in a generic $AdS_{d+1}/CFT_{d}$ scenario.

hep-th↗

arXiv2018

Entanglement negativity, Holography and Black holes

We investigate the application of our recent holographic entanglement negativity conjecture for higher dimensional conformal field theories to specific examples which serve as crucial consistency checks. In this context we compute the holographic entanglement negativity for bipartite pure and finite temperature mixed state configurations in $d$-dimensional conformal field theories dual to bulk pure $AdS_{d+1}$ geometry and $AdS_{d+1}$-Schwarzschild black holes respectively. It is observed that the holographic entanglement negativity characterizes the distillable entanglement for the finite temperature mixed states through the elimination of the thermal contributions. Significantly our examples correctly reproduce universal features of the entanglement negativity for corresponding two dimensional conformal field theories, in higher dimensions.

hep-th↗

arXiv2017

Holographic P-wave Superconductors in 1+1 Dimensions

We study $(1+1)$-dimensional p-wave holographic superconductors described by three dimensional Einstein-Maxwell gravity coupled to a massive complex vector field in the context of $AdS_3/CFT_2$ correspondence. In the probe limit where the backreation of matter fields is neglected, we show that there occurs a formation of a vector hair around the black hole below a certain critical temperature. In the dual strongly coupled $(1+1)$-dimensional boundary theory, this holographically corresponds to the formation of a charged vector condensate spontaneously breaking both the $U(1)$ and $SO(1,1)$ symmetries. We numerically compute the ac conductivity for the superconducting phase of the boundary field theory and find that the presence of a magnetic moment term in the dual bulk theory effects the conductivity in the boundary field theory.

hep-th↗

arXiv2017

Covariant holographic entanglement negativity

We propose a covariant holographic conjecture for the entanglement negativity of mixed states in bipartite systems described by $d$-dimensional conformal field theories dual to bulk non static $AdS_{d+1}$ configurations. Application of our conjecture to $(1+1)$-dimensional conformal field theories dual to bulk rotating BTZ black holes exactly reproduces the corresponding entanglement negativity in the large central charge limit and characterizes the distillable entanglement. We further demonstrate that our conjecture applied to the case of bulk extremal rotating BTZ black holes also characterizes the entanglement negativity for the chiral half of the corresponding zero temperature $(1+1)$-dimensional holographic conformal field theories.

hep-th↗

arXiv2017

Reissner Nordstrom Metric in Unimodular Theory of Gravity

We study the modified Reissner Nordstrom metric in the unimodular gravity. So far the spherical symmetric Einstein field equation in unimodular gravity has been studied in the absence of any source. We consider static electric and magnetic charge as source. We solve for Maxwell equations in unimodular gravitational background. We show that in unimodular gravity the electromagnetic field strength tensor is modified. We also show that the solution in unimodular gravity differs from the usual R-N metric in Einstein gravity with some corrections. We further study the thermodynamical properties of the R-N black-hole solution in this theory.

gr-qc↗

arXiv2017

Thermodynamic Geometry of Black Holes in the Canonical Ensemble

We investigate the thermodynamics and critical phenomena for four dimensional RN-AdS and Kerr-AdS black holes in the canonical ensemble both for the normal and the extended phase space employing the framework of thermodynamic geometry. The thermodynamic scalar curvatures for these black holes characterizes the liquid-gas like first order phase transition analogous to the van der Waals fluids, through the $R$-Crossing Method. It is also shown that the thermodynamic scalar curvatures diverge as a function of the temperature at the critical point.

hep-th↗

arXiv2016

Thermodynamic Geometry and Phase Transitions of AdS Braneworld Black Holes

The thermodynamics and phase transitions of charged RN-AdS and rotating Kerr-AdS black holes in a generalized Randall-Sundrum braneworld are investigated in the framework of thermodynamic geometry. A detailed analysis of the thermodynamics, stability and phase structures in the canonical and the grand canonical ensembles for these AdS braneworld black holes are described. The thermodynamic curvatures for both these AdS braneworld black holes are computed and studied as a function of the thermodynamic variables. Through this analysis we illustrate an interesting dependence of the phase structures on the braneworld parameter for these black holes.

hep-th↗

arXiv2016

Entanglement thermodynamics for charged black holes

The holographic quantum entanglement entropy for an infinite strip region of the boundary for the field theory dual to charged black holes in ${\cal A}dS_{3+1}$ is investigated. In this framework we elucidate the low and high temperature behavior of the entanglement entropy pertaining to various limits of the black hole charge. In the low temperature regime we establish a first law of entanglement thermodynamics for the boundary field theory.

hep-th↗

arXiv2016

Chaotic dynamics of strings in charged black hole backgrounds

We study the motion of a string in the background of Reissner-Nordstrom black hole, in both AdS as well as asymptotically flat spacetimes. We describe the phase space of this dynamical system through largest Lyapunov exponent, Poincare sections and basins of attractions. We observe that string motion in these settings is particularly chaotic and comment on its characteristics.

hep-th↗

arXiv2015

Thermodynamic geometry of holographic superconductors

We obtain the thermodynamic geometry of a (2+1) dimensional strongly coupled quantum field theory at a finite temperature in a holographic set up, through the gauge/gravity correspondence. The bulk dual gravitational theory is described by a (3+1) dimensional charged AdS black hole in the presence of a massive charged scalar field. The holographic free energy of the (2+1) dimensional strongly coupled boundary field theory is computed analytically through the bulk boundary correspondence. The thermodynamic metric and the corresponding scalar curvature is then obtained from the holographic free energy. The thermodynamic scalar curvature characterizes the superconducting phase transition of the boundary field theory.

hep-th↗

arXiv2015

p-wave Holographic Superconductors from Born-Infeld Black Holes

We obtain (2+1) dimensional p-wave holographic superconductors from charged Born-Infeld black holes in the presence of massive charged vector fields in a bulk $AdS_4$ Einstein-Born-Infeld theory through the $AdS_4$-$CFT_3$ correspondence. Below a certain critical transition temperature the charged black hole develops vector hair that corresponds to charged vector condensate in the strongly coupled (2+1) dimensional boundary field theory that breaks both the $U(1)$ symmetry as well as the rotational invariance. The holographic free energy is computed for the boundary field theory which shows that the vector order parameter exhibits a rich phase structure involving zeroth order, first order, second order and retrograde phase transitions for different values of the backreaction and the Born-Infeld parameters. We numerically compute the ac conductivity for the p-wave superconducting phase of the strongly coupled (2+1) dimensional boundary field theory which also depends on the relative values of the parameters in the theory.

hep-th↗

arXiv2014

Thermodynamic Geometry and Phase Transitions of Dyonic Charged AdS Black Holes

We investigate phase transitions and critical phenomena of four dimensional dyonic charged AdS black holes in the framework of thermodynamic geometry. In a mixed canonical grand canonical ensemble with a fixed electric charge and varying magnetic charge these black holes exhibit liquid gas like first order phase transition culminating in a second order critical point similar to the Van der Waals gas. We show that the thermodynamic scalar curvature R for these black holes follow our proposed geometrical characterization of the R-crossing Method for the first order liquid gas like phase transition and exhibits a divergence at the second order critical point. The pattern of R crossing and divergence exactly corresponds to those of a Van der Waals gas described by us in an earlier work.

hep-th↗