arXiv subjects

Subir Ghosh

Publications and source records attributed to Subir Ghosh.

At least 19 recordsLinked to original sources

arXiv2025

(Gravitational Wave) Memory of Starobinsky in a Time Crystal (Condensate)

In this Letter we have revealed the presence of Gravitational Wave Memory Effect (GWME) in a new and physically appealing scenario - the Time Crystal (TC) condensate of Starobinsky Quadratic Gravity. We have used a Gravitational Wave form, induced in a TC condensate in FLRW spacetime, that is much more general than the idealized and somewhat unphysical Plane Wave spacetimes, that are conventionally used. We have presented new results for non-zero GWME, both in coordinate and in velocity variables. The results are expressed in Cartesian and Brinkmann coordinates. Approximate analytic forms of transverse geodesics in Brinkmann coordinates are provided. Very rough quantitative estimates for GWME are also suggested.

gr-qc↗

arXiv2025

Relativistic Fluid Dynamics in Curved Spacetime: a Novel Effective Hamiltonian Approach

We present a comprehensive Eulerian (Hamiltonian) framework for relativistic fluid dynamics in curved spacetimes, with emphasis on Schwarzschild geometry. The key innovation lies in the consistent use of density and three-velocity fields, all defined in coordinate (Newtonian) time, while fully incorporating relativistic and curvature effects. {\it We stress that the entire dynamics is developed in coordinate (Eulerian) time, from the viewpoint of a static Eulerian observer.} In the non-relativistic regime, it is well known that Poisson brackets between the density $\rho(\vec{x}, t)$ and velocity fields $v^i(\vec{x}, t)$, together with an appropriate Hamiltonian, yield the continuity and Euler equations as Hamiltonian equations of motion. These field-theoretic Poisson brackets can be derived from canonical phase-space brackets defined on Lagrangian variables $(x_i, p_j)$, mapped to Eulerian fields $(\rho, v^i)$. We extend this framework to curved spacetime by constructing a relativistic version of the Eulerian Poisson algebra and proposing a corresponding Hamiltonian. This yields relativistic continuity and Euler equations valid in generic spacetimes, with evolution in coordinate time. Applying this to the Schwarzschild metric, we obtain exact stationary background solutions for radial flows and perform a perturbative stability analysis. We also introduce a generalised vorticity and examine its effect on perturbations over irrotational backgrounds, revealing its role in flow stability. This work offers a unified, first-principles Hamiltonian formulation of relativistic fluid dynamics in curved geometries, forming a foundation for further study of astrophysical and cosmological fluid phenomena.

gr-qc↗

arXiv2025

Gravitational Wave Propagation in a Geometric Condensate in Starobinsky Cosmology

In this paper we propose a new paradigm for cosmology: a time dependent scalar condensate background originated from the quadratic $(R + \alpha R^2)$ Starobinski model, where $R$ is the Ricci scalar and $\alpha$ the coupling constant. In weak gravity limit the system decouples into a conventional graviton and a higher derivative scalar. It was shown earlier through works from our group, \cite{ssg,sg,us}, that the latter can sustain an oscillatory lowest energy configuration or a {\it{Geometric Condensate}} as it consists entirely of metric degrees of freedom. In the present work, we study Gravitational Wave propagation in this condensate background. We show that the explicit time dependent nature of the condensate can generate curvature and radiation-like contributions in the scale factor evolution in FLRW cosmology. Subsequently the condensate leaves its signature on the Gravitational Wave profile as it propagates in the condensate modified FLRW spacetime. The wave profile is calculated analytically in terms of Whittaker functions. The main novelty of the Geometric Condensate scheme is that no external (condensate) matter from outside has been considered.

gr-qc↗

arXiv2024

Circuit Quantisation in Hamiltonian Framework: A Constraint Analysis Approach

In this work we apply Dirac's Constraint Analysis (DCA) to solve Superconducting Quantum Circuits (SQC). The Lagrangian of a SQC reveals the constraints, that are classified in a Hamiltonian framework, such that redundant variables can be removed to isolate the canonical degrees of freedom for subsequent quantization of the Dirac Brackets. We demonstrate the robustness of DCA unlike certain other set of ideas like null vector and loop charge which are each applicable only to specific types of quantum circuits.

quant-ph↗

arXiv2024

New Uncertainty Principle for a particle on a Torus Knot

The present work deals with quantum Uncertainty Relations (UR) subjected to the Standard Deviations (SD) of the relevant dynamical variables for a particle constrained to move on a torus knot. It is important to note that these variables have to obey the two distinct periodicities of the knotted paths embedded on the torus. We compute generalized forms of the SDs and the subsequent URs (following the Kennard-Robertson formalism). These quantities explicitly involve the torus parameters and the knot parameters where restrictions on the latter have to be taken into account. These induce restrictions on the possible form of wave functions that are used to calculate the SDs and URs and in our simple example, two distinct SDs and URs are possible. In a certain limit (thin torus limit), our results will reduce to the results for a particle moving in a circle. An interesting fact emerges that in the case of the SDs and URs, the local geometry of the knots plays the decisive role and not their topological properties.

quant-ph↗

arXiv2024

Explanation of the Generalizations of Uncertainty Principle from Coordinate and Momentum Space Periodicity

Generalizations of coordinate $x$-momentum $p_x$ Uncertainty Principle, with $\Delta x$ and $\Delta p_x$ dependent terms ($\Delta$ denoting standard deviation), $$\Delta x \Delta p_x\geq i\hbar (1+\alpha\Delta p_x^2 +\beta \Delta x^2)$$ have provided rich dividends as a poor person's approach towards Quantum Gravity, because these can introduce coordinate and momentum scales ($\alpha,\beta$ ) that are appealing conceptually. However, these extensions of Uncertainty Principle are purely phenomenological in nature. Apart from the inherent ambiguity in their explicit structures, the introduction of generalized commutations relations compatible with the the uncertainty relations has some drawbacks. In the present paper we reveal that these generalized Uncertainty Principles can appear in a perfectly natural way, in canonical quantum mechanics, if one assumes a periodic nature in coordinate or momentum space, as the case may be. We bring in to light quite old, (but not so well known), works by Judge and by Judge and Lewis, that explain in detail how a consistent and generalized Uncertainty Principle is induced in the case of angle $\phi$ - angular momentum $L_z$, $$\Delta \phi \Delta L_z \geq i\hbar (1 +\nu \Delta \phi^2)$$ purely from a consistent implementation of {\it{periodic}} nature of the angle variable $\phi $, without changing the $\phi, L_z$ canonical commutation relation. {\it{Structurally this is identical to the well known Extended Uncertainty Principle.}} We directly apply this formalism to formulate the $\Delta x \Delta p_x $ Extended Uncertainty Principle. We identify $\beta$ with an observed length scale relevant in astrophysics context. We speculate about the $\alpha$ extension.

quant-ph↗

arXiv2024

Spinning Black Hole in a Fluid

In this paper, we propose a new Analogue Gravity example - a spinning (or Kerr) Black Hole in an extended fluid model. The fluid model receives Berry curvature contributions and applies to electron dynamics in Condensed Matter lattice systems in the hydrodynamic limit. We construct the acoustic metric for sonic fluctuations that obey a structurally relativistic wave equation in an effective curved background. In a novel approach of dimensional analysis, we have derived explicit expressions for effective mass and angular momentum per unit mass in the acoustic metric (in terms of fluid parameters), to identify with corresponding parameters of the Kerr metric. The spin is a manifestation of the Berry curvature-induced effective noncommutative structure in the fluid. Finally we put the Kerr Black Hole analogy in a robust setting by revealing explicitly the presence of horizon and ergo-region for a specific background fluid velocity profile. We also show that near horizon behavior of the phase-space trajectory of a probe particle agrees with Kerr Black Hole analogy. In fluid dynamics perspective, presence of a horizon signifies the wave blocking phenomenon.

gr-qc↗

arXiv2023

Solving Superconducting Quantum Circuits in Dirac's Constraint Analysis Framework

In this work we exploit Dirac's Constraint Analysis (DCA) in Hamiltonian formalism to study different types of Superconducting Quantum Circuits (SQC) in a {\it{unified}} way. The Lagrangian of a SQC reveals the constraints, that are classified in a Hamiltonian framework, such that redundant variables can be removed to isolate the canonical degrees of freedom for subsequent quantization of the Dirac Brackets via a generalized Correspondence Principle. This purely algebraic approach makes the application of concepts such as graph theory, null vector, loop charge,\ etc that are in vogue, (each for a specific type of circuit), completely redundant. The universal validity of DCA scheme in SQC, proposed by us, is demonstrated by correctly re-deriving existing results for different SQCs, obtained previously exploiting different formalisms each applicable for a specific SQC. Furthermore, we have also analysed and predicted new results for a generic form of SQC - it will be interesting to see its validation in an explicit circuit implementation.

quant-ph↗

arXiv2023

Acoustic Kerr Metric in Analogue Gravity

The present paper is based on a previous work (involving two of the present authors) where a generalized fluid dynamical model was proposed. The underlying symplectic structure of the Lagrangian discrete degrees of freedom obeyed a Non-Commutative algebra, generated by Berry curvature correction. In an Euler (or Hamiltonian) framework, this is manifested as an extended algebra between the fluid variables, leading to the extended fluid model. Here we study the dynamics of sonic fluctuations that live in this effective analogue gravity spacetime. Interestingly enough, the effective metric resembles that of a spinning Black Hole; the spin is induced by the underlying Non-Commutative structure. The effective mass and spin parameters of the Black Hole, in terms of fluid parameters, are also identified. The connection of our model with anomalous Hall systems may lead to observable signatures of the analogue black hole in physical systems.

gr-qc↗

arXiv2023

Cosmology in $R^2$-gravity: Effects of a Higher Derivative Scalar Condensate Background

A well known extension of Einstein General Relativity is the addition of an $R^2$-term, which is free of ghost excitations and in the linearized framework, reduces Einstein General Relativity and an additional higher derivative scalar. According to \cite{Chakraborty:2020ktp}, the above scalar sector can sustain a Time Crystal-like minimum energy state, with non-trivial time dependence. Exploiting previous result that the scalar can sustain modes with periodic time dependence in its lowest energy, we consider this condensate as a source and study the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) cosmology in this background. The effect of the $R^2$-term is interpreted as a back reaction. A remarkable consequence of the condensate is that, irrespective of open or close geometry of the Universe, for an appropriate choice of parameter window, the condensate can induce a decelerating phase before the accelerated expansion starts and again, in some cases, it can help to avoid the singularity in the deceleration parameter (that is present in conventional FLRW Cosmology).

gr-qc↗

arXiv2022

Quantum gases on a torus

This manuscript is aimed at studying the thermodynamic properties of quantum gases confined to a torus. To do that, we consider \textit{noninteracting} gases within the grand canonical ensemble formalism. In this context, fermoins and bosons are taken into account and the calculations are properly provided in both analytical and numerical manners. In particular, the system turns out to be sensitive to the topological parameter under consideration: the winding number. Furthermore, we also derive a model in order to take into account \textit{interacting} quantum gases. To corroborate our results, we implement such a method for two different scenarios: a ring and a torus.

quant-ph↗

arXiv2021

Divergence Anomaly and Schwinger Terms: Towards a Consistent Theory of Anomalous Classical Fluid

Anomaly, a generic feature of relativistic quantum field theory, is shown to be present in non-relativistic classical ideal fluid. A new result is the presence of anomalous terms in current algebra, an obvious analogue of Schwinger terms present in quantum field theory. We work in Hamiltonian framework where Eulerian dynamical variables obey an anomalous algebra (with Schwinger terms) that is inherited from modified Poisson brackets, with Berry curvature corrections, among Lagrangian discrete coordinates. The divergence anomaly appears in the Hamiltonian equations of motion. A generalized form of fluid velocity field can be identified with the "anomalous velocity" of Bloch band electrons appearing in quantum Hall effect in condensed matter physics. We finally show that the divergence anomaly and Schwinger terms satisfy well known Adler consistency condition. Lastly we mention possible scenarios where this new anomalous fluid theory can impact.

hep-th↗

arXiv2021

Quantum corrections enhance chaos: study of particle motion near a generalized Schwarzschild black hole

The paper is devoted to a detailed study of the effects of quantum corrections on the chaotic behavior in the dynamics of a (massless) probe particle near the horizon of a generalized Schwarzschild black hole. Two possible origins inducing the modification of black hole metric are considered separately; the noncommutative geometry inspired metric (suggested by Nicolini, Smailagic and Spallucci) and the metric with quantum field theoretic corrections (derived by Donoghue). Our results clearly show that in both cases, the metric extensions favour chaotic behavior, namely chaos is attained for relatively lower particle energy. This is demonstrated numerically by exhibiting the breaking of the KAM tori in Poincar\'e sections of particle trajectories and also via explicit computation of the (positive) Lyapunov exponents of the trajectories.

gr-qc↗

arXiv2021

Fermions on a torus knot

In this work, we investigate the effects of a nontrivial topology (and geometry) of a system considering \textit{interacting} and \textit{noninteracting} particle modes, which are restricted to follow a closed path over the torus surface. In order to present a prominent thermodynamical investigation of this system configuration, we carry out a detailed analysis using statistical mechanics within the grand canonical ensemble approach to deal with \textit{noninteracting} fermions. In an analytical manner, we study the following thermodynamic functions in such context: the Helmholtz free energy, the mean energy, the magnetization and the susceptibility. Further, we take into account the behavior of Fermi energy of the thermodynamic system. Finally, we briefly outline how to proceed in case of \textit{interacting} fermions.

cond-mat.quant-gas↗

arXiv2021

Uncertainty Relations for the Relativistic Jackiw-Nair Anyon: A First Principles Derivation

In this paper we have explicitly computed the $position-position$ and $position-momentum$ (Heisenberg) Uncertainty Relations for the model of relativistic particles with arbitrary spin, proposed by Jackiw and Nair ref.[1] as a model for Anyon, in a purely quantum mechanical framework. This supports (via Schwarz inequality) the conjecture that anyons live in a 2-dimensional \textit{noncommutative} space. We have computed the non-trivial uncertainty relation between anyon coordinates, ${\sqrt{\Delta x^2\Delta y^2}}=\hbar\bar{\Theta}_{xy}$, using the recently constructed anyon wave function ref.[6], in the framework of ref.[7]. We also compute the Heisenberg (position-momentum) uncertainty relation for anyons. Lastly we show that the identical \textit{formalism} when applied to electrons, yield a trivial position uncertainty relation, consistent with their living in a 3-dimensional commutative space.

hep-th↗

arXiv2021

Quantum Back Flow Across a Black Hole Horizon in a Toy Model Approach

Quantum Back Flow (QBF), discovered quite a few years back, is a generic purely quantum phenomenon, in which the probability of finding a particle in a direction is non-zero (and increasing for a certain period of time) even when the particle has with certainty a velocity in the opposite direction. In this paper, we study QBF of a quantum particle across the event horizon of a Schwarzschild Black Hole. In a toy model approach, we consider a superposition of two ingoing solutions and observe the probability density and probability current. We explicitly demonstrate a non-vanishing quantum backflow in a small region around the event horizon. This is in contrast to the classical black hole picture, that once an excitation crosses the horizon, it is lost forever from the outside world. Deeper implications of this phenomenon are speculated. We also study quantum backflow for another spacetime with a horizon, the Rindler spacetime, where the phenomenon can be studied only within the Rindler wedge.

hep-th↗

arXiv2020

Entanglement Induced by Noncommutativity: Anisotropic Harmonic Oscillator in Noncommutative space

Quantum entanglement, induced by spatial noncommutativity, is investigated for an anisotropic harmonic oscillator. Exact solutions for the system are obtained after the model is re-expressed in terms of canonical variables, by performing a particular Bopp's shift to the noncommuting degrees of freedom. Employing Simon's separability criterion, we find that the states of the system are entangled provided a unique function of the (mass and frequency) parameters obeys an inequality. Entanglement of Formation for this system is also computed and its relation to the degree of anisotropy is discussed. It is worth mentioning that, even in a noncommutative space, entanglement is generated only if the harmonic oscillator is anisotropic. Interestingly, the Entanglement of Formation saturates for higher values of the deformation parameter $\theta$, that quantifies spatial noncommutativity.

quant-ph↗

arXiv2020

Stimulated Hawking Emission From Electromagnetic Analogue Black Hole: Theory and Observation

In this paper we consider possible analogue Hawking radiation from a normal dielectric and metamaterial composite, having an analogue horizon where the dielectric parameters vanish and change sign upon crossing this transition zone. We follow a complex path analysis to show the presence of an analogue Hawking temperature at the horizon and subsequent photon production from the ambient electromagnetic field. Possibility of experimental observation is also commented upon.

hep-th↗