arXiv subjects

Sunandan Gangopadhyay

Publications and source records attributed to Sunandan Gangopadhyay.

At least 37 records · Page 2Linked to original sources

arXiv2025

Noncommutative $p$-wave holographic superconductors

In this work, we have studied the effects of noncommutative geometry on the properties of p-wave holographic superconductors with massive vector condensates in the probe limit. We have applied the Stürm-Liouville eigenvalue approach to analyse the model. In this model, we have calculated the critical temperature and the value of the condensation operator for two different values of $m^2$. We have also shown how the influence of noncommutative geometry modifies these quantities. Finally, by applying a linearised gauge field perturbation along the boundary direction, we calculated the holographic superconductor's AC conductivity using a self-consistent approach and then carried out a more rigorous analysis. The noncommutative effects are also found to be present in the result of AC conductivity. We have also found that just like the commutative case, here the DC conductivity diverges due to the presence of a first order pole in the frequency regime.

hep-th↗

arXiv2025

Barrow holographic dark energy interacting model in the presence of radiation and matter

We have studied the effect of dynamical radiation in the interacting barrow holographic dark energy model for a non-flat universe. For both open and closed universes, we have obtained the evolution equation for the energy density parameters for dark energy, dark matter and radiation for four different kinds of interaction among the seven possible linear phenomenological interactions. We have then numerically solved those coupled differential equations to show their behaviour with the redshift parameter. Also, the dynamics of the dark energy equation of state parameter with redshift for different interaction models are shown. For all four interaction models, it is also found that for higher values of the Barrow exponent, the dark energy equation of state parameter shows a transition into the phantom region from the quintessence region in the early time, that is, for lower redshift values. We have also found different epochs corresponding to dark energy-dark matter, dark energy-radiation and dark matter-radiation crossings. These crossing points are also consistent with the thermal history of the universe. We have also obtained various observational constraints for different cosmological parameters for our interacting Barrow holographic dark matter model using the Cosmic chronometer, Baryon Acoustic Oscillator and Pantheon+ data sets. The constraint values of the Hubble parameter in our cosmological shows higher values compared to the $Λ$CDM model, therefore indicating towards a possible resolution to the Hubble tension problem.

gr-qc↗

arXiv2025

Relativistic quantum Otto engine driven by the circular Unruh effect

In this work, we present a new framework for a relativistic quantum analouge of the classical Otto engine. Considering a single qubit as the working substance, we analyse its interaction with a massless quantum scalar field while undergoing two half-circular rotations at ultra-relativistic velocities. The quantum vacuum serves as a thermal bath through the Unruh effect induced due to the acceleration from the circular motions. We observe that the response function of the qubit gets significantly modified by the presence of the qubit's trajectory. Analysing the transition probability behaviour, we find that in the high-acceleration regime, it asymptotically approaches a constant value, determined solely by the properties of the correlation function. Furthermore, our results emphasize the crucial role of the circular trajectory in determining the engine's work output. In particular, the extracted work increases with detector acceleration and approaches an asymptotic limit in the high-acceleration regime. Notably, the efficiency of this model remains unaffected by the circular motion and is consistent with previously studied models.

quant-ph↗

arXiv2025

Renormalization group improved cosmology in the presence of a stiff matter era

In \href{https://link.aps.org/doi/10.1103/PhysRevD.92.103004}{Phys. Rev. D 92 (2015) 103004}, simple analytical solutions of the Friedman equations were obtained for a universe having stiff matter component in the early universe together with a dark matter, and a dark energy component. In this analysis, the universe is considered to be made of a dark fluid which behaves as a stiff matter in the early phase of the universe (when the internal energy dominates). It is also more logical to consider quantum gravitational effects in the early phase of the cosmological evolution. In this analysis, following \href{https://link.aps.org/doi/10.1103/PhysRevD.65.043508}{Phys. Rev. D 65 (2002) 043508}, we consider renormalization group improved modified Friedmann equations where the Newton's gravitational constant (G) and the cosmological constant (Λ) flows with the momentum scale of the universe. It is observed that for a universe undergoing a stiff matter era, radiation era, and matter era, inflation is absent in the early time regime of the universe when the flow of the Newton's gravitational constant and cosmological constant is under consideration. Using the identification of the momentum scale with the scale factor of the universe, we then explore the era $t>t_{\text{Pl}}$ which indicates a primarily matter dominated era with accelerated expansion due to the presence of dark energy. Finally, considering the total equation of state as a combination of linear equation of state along with a polytropic equation of state, we observe that after the Planck-time the universe can undergo an inflationary phase and we find out that the inflation is enhanced by quantum gravitational effects arising due to the consideration of renormalization group approach to quantum gravity

gr-qc↗

arXiv2025

Investigating the role of mutual information in the Page curve for a functional renormalization group improved Schwarzschild black hole

The present work delves into probing the importance of mutual information of relevant subsystems in obtaining the correct time-evolution of fine-grained entropy of Hawking radiation, as suggested by Page. This was done by considering a functional renormalization group improved or simply, quantum corrected Schwarzschild black solution which captures the flavour of an effective theory of quantum gravity. The mentioned black hole solution emerges from a asymptotically safe average effective action which describes a trajectory in momentum-space and satisfies a renormalizarion group equation. Furthermore, in the before Page time scenario, the behaviour of the mutual information between appropriate subsystems over time leads to the Hartman-Maldacena time. The observations made for the quantum corrected Schwarzschild black hole have been compared to the same made for the standard Schwarzschild black hole in order to draw some novel conclusions. Based upon our observations, we also propose a formula for computing fine-grained entropy of Hawking radiation for an eternal black hole, in presence of the island.

hep-th↗

arXiv2025

A holographic realization of correlation and mutual information

The status of the inequality existing between mutual information and (normalized) thermal two-point connected correlation function, namely, $I(A:B)\ge\frac{(\expval{\mathcal{O}_{A}\mathcal{O}_{B}}_β-\expval{\mathcal{O}_{A}}_β\expval{\mathcal{O}_{B}}_β)^2}{2\expval{\mathcal{O}_{A}^2}_β\expval{\mathcal{O}_{B}^2}_β}$ has been explicitly probed by using the gauge/gravity correspondence. In the holographic analysis, the geodesic approximation for heavy operators ($Δ\sim mR$) has been used. We observe that the study leads to some non-trivial insights depending upon the method of calculating the thermal object $\expval{\mathcal{O}^2}_β$. For a particular computed result of $\expval{\mathcal{O}^2}_β$ we propose that all of the existing quantum mechanical dependencies (correlations) and classical correlations between the subsystems $A$ and $B$ vanishes at two different separation lengths, namely, $sT|c$ and $sT|_I$ where $sT|_I>sT|_c$.

hep-th↗

arXiv2025

Derivative coupling in horizon brightened acceleration radiation: a quantum optics approach

Horizon Brightened Acceleration Radiation (HBAR) signifies a unique radiation process and provides a promising framework in exploring acceleration radiation in flat/ curved spacetime. Its construction primarily relies on the transition probability of an atom falling through a high-Q cavity while interacting with a quantum field. The HBAR effect has typically been explored in the context of minimal coupling between the atom and the field amplitude. However, the minimally coupled models are affected by the infrared (IR) divergences that arise in the massless limit of the quantum fields in (1+1) dimensions. Thus, in the present manuscript, we examine the HBAR process using both the point-like and finite size detectors coupled with the momentum of the field, which plays a crucial role in naturally resolving IR divergences. Our results suggest that the transition probability for the point-like detector is independent of its frequency. This can be interpreted as the influence of the local gravitational field which modifies the sensitivity of the detector to its frequency and broadens its effective frequency range. Through a comparative study based on the length of the detector, we find that for a detector with a smaller length, the steady state solution for the density matrix of the field vanishes. This may indicate the existence of a non equilibrium thermodynamic state under the condition of finite size detector-field interaction. These distinctive features are exclusive to the derivative coupling between the atom and the field, highlighting them as a compelling subject for future investigation.

gr-qc↗

arXiv2025

Holographic entanglement entropy and complexity for the cosmological braneworld model

In a recent study \cite{Park:2020jio}, the time-dependent entanglement entropy of the universe undergoing expansion according to various power laws has been analyzed within the framework of the braneworld model. The results of the entanglement entropy in that paper take into account only the effects of a radiation and a matter-dominated universe. In this work, we have computed the time-dependent entanglement entropy and complexity of the FLRW universe in the presence of different matter sources (radiation, matter and some exotic matter). In contrast to the approach in \cite{Park:2020jio}, all the calculations in this paper have been carried out in a perturbative manner in the framework of braneworld model of cosmology. According to this model, our universe is situated on a brane and different matter sources appear on the brane due to the back reaction of different $p$-brane gas configurations in the bulk spacetime. By considering the bulk spacetime as a black brane geometry, we have considered different blackening factors corresponding to radiation, matter, and exotic matter and calculated entanglement entropy and complexity holographically. In the braneworld model, the universe's expansion is described by the brane's time-dependent radial position. This position is determined using the second Israel junction condition for various matter sources. The time evolution of entanglement entropy and complexity is then obtained by substituting this brane position. We have also shown the dependence of entanglement entropy and complexity on the cosmological time for all the different matter-dominated universes in the early and late time eras. Even though the calculations of holographic entanglement entropy and complexity are done perturbatively, the results remain consistent with those of \cite{Park:2020jio}.

hep-th↗

arXiv2025

Area spectrum and black hole thermodynamics

The role of horizon area quantization on black hole thermodynamics is investigated in this article. The coefficient appearing in the quantization of area is fixed by an appeal to the saturated form of the Landauer's principle. Then by considering transition between discrete states of the event horizon area which in turn is equivalent to transitions between discrete mass states of the black hole, the change in the mass can be obtained. The change in mass is then equated to the product of the Hawking temperature and change in entropy of the black hole between two consecutive discrete states applying the first law of black hole thermodynamics. This gives the corrected Hawking temperature. In particular, we apply this technique to the Schwarzschild black hole, the quantum corrected Schwarzschild black hole, the Reissner-Nordström black hole which is a charged black hole, and the rotating Kerr black hole geometry, and obtain the corrected Hawking temperature in each of these cases. We then take a step forward by inserting this corrected Hawking temperature in the first law of black hole thermodynamics once again to calculate the entropy of the black hole in terms of the horizon area of the black hole. This leads to logarithmic and inverse corrections to the entropy of the black hole.

gr-qc↗

arXiv2025

Inverse logarithmic correction in the HBAR entropy of an atom falling into a renormalization group improved charged black hole

In this work, we have considered a spherically symmetric non-rotating charged black hole geometry where both the Newton's gravitational constant and the charge of the black hole flows with the energy scale. We have used the Kretschmann scale identification to write down the finite cutoff for the momentum scale in terms of the proper distance. Introducing the flow of running couplings, the event horizon radius of the black hole using quantum improved Reissner-Nordstrom metric was found in \href{https://doi.org/10.1103/PhysRevD.104.066016}{Phys. Rev. D 104 (2021) 066016}. We have, in this work, explored the thought experiment of a two-level atom freely falling into the event horizon of a quantum improved charged black hole and have computed the transition probability of the atom for going from its ground state to the excited state via emission of a virtual photon. We find that the probability deviates slightly from the pure Planckian spectrum. We have showed that this deviation is due to the presence of incomplete lower gamma function in the distribution function. We have then computed the horizon brightened acceleration radiation entropy and found that it is identical to the Bekenstein-Hawking entropy followed by the renormalization group correction terms including an inverse logarithmic and a square root of the area term due to emitting photons.

gr-qc↗

arXiv2025

Current and quantum transport factor of fermionic system in fermionic bath

This paper explores the dynamics of current and the quantum transport factor in a fermionic system with a central oscillator interacting with two fermionic reservoirs at different temperatures. We derive the master equation for the system density matrix, accounting for energy exchange between the system and the reservoirs. The current is analyzed in relation to system parameters and reservoir temperatures, revealing that the quantum transport factor differs from classical systems, approaching Carnot efficiency at high temperatures but being different at low temperatures. We also examine the power spectrum of the current, providing insights into current fluctuations and their temperature dependence. Furthermore, we derive the Fokker-Planck equation and the Glauber-Sudarshan P-representation, where the steady-state probability distribution takes a Gaussian form, confirming the system behaves like a harmonic oscillator. This work advances the understanding of quantum transport in fermionic systems and provides a foundation for future research in quantum thermodynamics.

quant-ph↗

arXiv2025

Quantum nature of gravity in a Bose-Einstein condensate

The effect of noise induced by gravitons on a Bose-Einstein condensate has been explored in (Phys. Rev. D 110 (2024) 026014; https://link.aps.org/doi/10.1103/PhysRevD.110.026014). In the previous paper, we investigated the effects of graviton while detecting a gravitational wave using a Bose-Einstein condensate. In this work we shall explicitly calculate the decoherence due to the noise of gravitons between two momentum states of the Bose-Einstein condensate. This decoherence happens due to Bremsstrahlung from the Bose-Einstein condensates due to the effect of the noise induced by gravitons. It is also observed that the two states become entangled because of the existence of a surrounding graviton field which degrades over time via means of this gravitational Bremsstrahlung. Using this property of the Bose-Einstein condensate in a quantum gravity background, we propose an experimental test via the use of atom lasers (generated from the condensate) which would, in principle, help to detect gravitons in future generations of very advanced ultra-cold temperature experiments.

hep-th↗

arXiv2025

Thermodynamics of a Schwarzschild black hole surrounded by quintessence in the generalized uncertainty principle framework

We investigate the thermodynamics of a Schwarzschild black hole, surrounded by the quintessence energy-matter in the linear and quadratic generalized uncertainty principle framework. Considering the variance in the position to be of the order of the event horizon radius and equating the variance in the momentum to the Hawking temperature of the black hole, we substitute these variances in the deformed algebra. From there we obtained the generalized uncertainty principle-modified black hole temperature and eventually the specific heat of the black hole. Then we calculate the critical as well as the remnant mass and obtain the entropy relation. We observe that the entropy relation includes the usual leading order ``\textit{area divided by four}" term, sub-leading logarithmic term, and higher order inverse of the area corrections. Finally, calculating the energy output as a function of time, we obtain the evaporation time of the black hole. The results show the dependence of the quintessence parameter on the thermodynamic quantities in the framework of linear and quadratic generalized uncertainty principle.

gr-qc↗

arXiv2025

Dirac equation in a gauge-field background in the Moyal plane

Starting with the Dirac equation for an electron in a constant electromagnetic background on a noncommutative (NC) plane, we obtain a gauge invariant description of the system. Surprisingly, the dynamics of the system is dictated by the standard form of Lorentz force law, once the effective magnetic and electric fields $\left( B^{NC}, \, E^{NC} \right)$ correct up to leading order in the NC parameter are identified. The Hall effect is studied using the NC corrected fields in the non-relativistic (NR) limit. This shows that noncommutativity affects the cyclotron frequency, but leaves the Hall conductivity unaffected at least to first order in the NC parameter. Owing to the NC corrected magnetic field, the hyperfine splitting of Hydrogen atom spectrum also shows a first order correction which helps establish an upper bound on the spatial NC parameter.

hep-th↗

arXiv2025

Current, quantum transport and entropic force of bosonic systems interacting with two thermal reservoirs

This paper investigates the dynamics of current and quantum transport factor in a bosonic system consisting of a central system interacting with two reservoirs at different temperatures. We derive a master equation describing the time evolution of the density matrix of the system, accounting for the interactions and energy transfer between the components. We quantify the current, representing the flow of bosons through the system and analyse its dependence on the system's parameters and temperatures of the thermal reservoirs. In the steady state regime, we derived an expression for the quantum transport factor of the energy transfer process. Our analysis show that quantum effects, such as the dependence on temperature can significantly impact this factor. In particular, we observe that the transport factor of the quantum system is greater than the corresponding factor when the temperature goes to infinity, where the factor has an identical form with the Carnot efficiency of an ideal heat engine. We then derived the Fokker-Planck equation to find out the Glauber-Sudarsan $P$-representation. In the steady state of the equation, the probability distribution comes out to be in Gaussian form. We then calculated the entropic force for this probability distribution which gives the Hooke's law in the steady state, in agreement with the fact that our system is a harmonic oscillator.

quant-ph↗

arXiv2024

Quantum coherence measures for generalized Gaussian wave packets under a Lorentz boost

In this paper we consider a single particle, spin-momentum entangled state and measure the effect of relativistic boost on quantum coherence. The effect of the relativistic boost on single-particle generalized Gaussian wave packets is studied. The coherence of the wave function as measured by the boosted observer is studied as a function of the momentum and the boost parameter. Using various formulations of coherence, it is shown that in general the coherence decays with the increase in momentum of the state, as well as the boost applied to it. A more prominent loss of coherence due to relativistic boost is observed for a single particle electron than that of a neutron. The analysis is carried out with generalized Gaussian wave packet of the form $\mathcal{N} p^n \exp(-\frac{p^2}{σ^2})$ with $n$ being the ``generalization parameter" and $\mathcal{N}$ denoting the appropriate normalization constant. We also obtain a range for parameter $n$ appearing in the wave packet. The upper bound is found to have a dependence on the mass of the particle and the width of the Gaussian wave packet. We have obtained the Frobenius-norm measure of coherence, $l_1$ and $l_2$ norm measure of coherence, and relative entropy of coherence for a (1+1) and (3+1)-dimensional analysis. Corresponding to each of the cases, we observe that the $l_1$ norm measure of coherence is equal to the Frobenius norm measure of coherence. We have analyzed the scenario for which such a beautiful coincidence can occur. Finally, we have plotted different measures of coherence for the electron as well as the neutron for different values of the width of the wave-function $σ$, boost parameter $β$, and generalization parameter $n$.

quant-ph↗

arXiv2024

Gauss-Bonnet AdS planar and spherical black hole thermodynamics and holography

In this work, we extend the study in \href{https://link.springer.com/article/10.1007/JHEP11(2022)013}{JHEP11(2022)013} incorporating the AdS/CFT duality to establish a relationship between the local temperatures (Tolman temperatures) of a large (AdS) spherical and a (AdS) planar Schwarzschild black hole near the AdS boundary considering Gauss-Bonnet curvature correction in the gravitational action. We have shown that the higher curvature corrections appear in the local temperature relationship due to the inclusion of Gauss-Bonnet term in the bulk. By transforming the metric into Fefferman-Graham form, we have calculated the energy density of the conformal fluid at the boundary. The obtained result contains finite coupling corrections which are holographically induced by the Gauss-Bonnet curvature correction in the bulk theory. Following the well known approach of fluid/gravity duality, the energy density of the conformal fluid at the boundary is then compared with the black body radiation energy density. This comparison shows that the energy density is proportional to the temperature of the conformal fluid. The temperature of the conformal fluid is then shown to be related to the Tolman temperature of the black hole which then eventually helps us to establish both the Hawking temperature and Tolman temperature relationship between large spherically symmetric and planar Schwarzschild black holes in Gauss-Bonnet gravity near the AdS boundary.

hep-th↗

arXiv2024

Information theoretic measures for Lifshitz system

In this work, we have studied various mixed state information theoretic quantities for an excited state of Lifshitz spacetime in $3+1$-dimensions. This geometry is the gravity dual to a class of $2+1$-dimensional quantum field theories having Lifshitz symmetry. We have holographically calculated mutual information, entanglement wedge cross section, entanglement negativity and mutual complexity for strip like subsystems at the boundary. For this we have used the results of holographic entanglement entropy and complexity present in the literature. We first calculate all of these mentioned quantities for the pure state of Lifshitz spacetime. Then we have moved on to calculate all these quantities for excited state of the Lifshitz spacetime. The gravity dual of excited state of Lifshitz systems in field theory can be obtained by applying constant perturbations along the boundary direction. Further, we would like to mention that for the simplicity of calculation we are only considering results up to the first order in perturbation. The change in the obtained holographic information theoretic quantities are then related to entanglement entropy, entanglement pressure, entanglement chemical potential and charge using the stress tensor complex. These relations are analogous to the first law of entanglement thermodynamics given earlier in the literature. All the calculations are carried out for both values of dynamical scaling exponent ($z$) present in the Lifshitz field theory.

hep-th↗