arXiv subjects

Dragoljub Gočanin

Publications and source records attributed to Dragoljub Gočanin.

18 recordsLinked to original sources

arXiv2026

Bell nonlocality from twisted statistics

We investigate Bell correlations for a free real quantum scalar field on the noncommutative Moyal plane. Although the free field dynamics and the one-particle sector remain unchanged, the deformation enters through twisted multiparticle statistics and its Fock-space dressing representation. A classical external source coupled locally to the twist-dressed quantum field prepares coherent superpositions of momentum-pair configurations propagating toward two spacelike-separated laboratories. The momentum-dependent twist phases are generally nonfactorizable and generate entanglement between the corresponding wave-packet modes. We show that suitable local mode measurements lead to a violation of the CHSH Bell inequality. The resulting correlations provide an operational probe of the noncommutative structure encoded in the multiparticle sector of the quantum field.

quant-ph↗

arXiv2026

Twisted holographic superconductors in external magnetic field

Among the various applications of the AdS/CFT correspondence in condensed matter physics, the realization of the phase transition between the normal and superconducting phases in holographic quantum field theory is of particular importance. Following seminal papers on holographic superconductors that introduced the basic framework, one major line of development has focused on capturing the Meissner effect with all relevant parameters, which requires the inclusion of an external magnetic field. Although a complete holographic description of a superconductor is still lacking, the basic elements of the gravitational systems dual to what can most accurately be characterized as a charged superfluid have been established. Using holographic setups to describe three- and four-dimensional superconductors, we investigate the effect of noncommutative twist deformation of bulk fields on the phase transition parameters, such as the critical magnetic field. In a broader context, our results represent the first systematic attempt to elucidate the role of noncommutative gauge field theory as part of the bulk description of condensed matter systems.

hep-th↗

arXiv2026

Rotating frames from quantum deformed spacetime

In a sense of deformation quantization, noncommutative (NC) geometry introduces a quantum structure of spacetime. Using the twist-deformation formalism, we show that the dynamical effects of spacetime noncommutativity can amount to a transition to a rotating frame of reference. In particular, we study the dynamics of charged matter (scalars and spinors) on the curved background of Melvin's electric universe in the framework of NC gauge field theory. Melvin's electric/magnetic universe is an exact sourceless solution of the Einstein-Maxwell field equations that is both static and axially symmetric, and it represents a parallel bundle of self-gravitating electric/magnetic flux. Due to its axial symmetry, it allows for a special kind of Killing twist that does not affect the coupling of the matter fields to the background metric. Focusing on the perturbative NC equations of motion for charged scalars and Dirac spinors coupled to Melvin's electric background, we show that they have the same form as the corresponding classical (undeformed) equations of motion coupled to the same geometric background but in a uniformly rotating frame whose angular velocity is determined by the NC scale and the electric charge of the matter field. In principle, this NC rotation effect can be experimentally tested by setting up the Sagnac interferometry apparatus to measure the Sagnac phase shift for charged versus electrically neutral particles, thus placing a bound on the scale of spacetime noncommutativity.

hep-th↗

arXiv2026

Entangled quantum clocks as operational probes of spacetime curvature

Building on the framework developed by Perche [Phys. Rev. D 106, 025018 (2022)], we study two localized nonrelativistic quantum particles propagating along timelike geodesics in a curved spacetime background. Each particle is coupled to a quantum clock that operationally records the time spent in a prescribed spatial region. We compute the covariance of the resulting time observables for separable and entangled two-particle states, comparing flat and curved backgrounds. We then reformulate the protocol as a Bell-like experiment and show that the Bell parameter can acquire a curvature-induced correction. In particular, a protocol calibrated to saturate the classical bound in flat spacetime can be driven above this bound in curved spacetime for entangled states. We focus on two-dimensional curved backgrounds in which the local tidal term induces an effective harmonic potential in the Fermi-frame description. Our results show that spacetime curvature can modify operationally defined quantum correlations and suggest entangled quantum clocks as probes of spacetime curvature.

quant-ph↗

arXiv2026

The role of torsion in holographic conductivity

Generalizing the usual setup for holographic duality, where bulk spacetime is described by pseudo-Riemannian geometry, we consider a Riemann-Cartan bulk with non-trivial torsion as a background for an electromagnetic gauge field dual to $U(1)$ boundary current. Working in the probe limit, we explore how the bulk torsion, which induces spin current at the boundary, affects the electric conductivity of the boundary theory. We consider standard types of non-minimal couplings between torsion and the electromagnetic field found in the literature, and the results indicate that these torsion couplings are more suitable candidates, compared to the common minimal coupling regime, for a holographic description of the existing experimental findings regarding conductivity.

hep-th↗

arXiv2026

Holographic entanglement entropy in Chern-Simons gravity with torsion

Holographic entanglement entropy is a key concept linking quantum information theory and gravity. Since the original conjecture of Ryu and Takayanagi, holographic entanglement entropy has been generalized beyond Einstein--Hilbert gravity to include higher-curvature corrections. In most existing generalizations, however, it is implicitly assumed that the bulk spacetime geometry is Riemannian, i.e. torsion-free. Here we propose a prescription for incorporating torsion into holographic entanglement entropy in the boundary theory dual to five-dimensional Chern--Simons gravity. We argue that the entanglement entropy acquires an additional universal divergent term proportional to the logarithm of the UV cutoff, and that this term is generated solely by torsion.

hep-th↗

arXiv2025

Boundary terms, branes and AdS/BCFT in first-order gravity

We provide an account of the issue of Gibbons-Hawking-York-like boundary terms for a gravity theory defined on a Riemman-Cartan spacetime. We further discuss different criteria for introducing boundary terms in some familiar first-order gravity theories with both on-shell vanishing and non-vanishing torsion, along with considerations regarding the thermodynamics of black holes and profiles of the End-of-the-World branes. Our analysis confirms the expected geodesic profile of the End-of-the-World brane in the BF formulation of Jackiw-Teitelboim gravity. Finally, we present the first realisation of the AdS/BCFT duality for spacetime with torsion.

hep-th↗

arXiv2023

Testing the Braneworld Theory with Identical Particles

Various attempts to go beyond the theory of General Relativity start from the assumption that spacetime is not a 4-dimensional but rather a higher-dimensional manifold. Among others, braneworld scenarios postulate that the spacetime we effectively observe is actually a 4-dimensional brane embedded in a higher-dimensional spacetime. In general, braneworld models predict a departure from the Newton gravity law in the nonrelativistic regime. Based on this fact, we propose an experimental test that uses a pair of gravitationally interacting identical particles to determine the validity of certain braneworld models and provide numerical results that should be compared with experimental data. In particular, we consider the Randal-Sundrum braneworld model and study two cases of 5-dimensional gravity theories: the Einstein-Hilbert gravity with the negative cosmological constant and the Einstein-Gauss-Bonnet (nearly-Chern-Simons) gravity.

gr-qc↗

arXiv2023

Noncommutative $SO(2,3)_{\star}$ Gauge Theory of Gravity

Topological gravity (in the sense that it is metric-independent) in a $2n$-dimensional spacetime can be formulated as a gauge field theory for the AdS gauge group $SO(2,2n-1)$ by adding a multiplet of scalar fields. These scalars can break the gauge invariance of the topological gravity action, thus making a connection with Einstein's gravity. This review is about a noncommutative (NC) star-product deformation of the four-dimensional AdS gauge theory of gravity, including Dirac spinors and the Yang-Mills field. In general, NC actions can be expanded in powers of the canonical noncommutativity parameter $θ$ using the Seiberg-Witten map. The leading-order term of the expansion is the classical action, while the higher-order $θ$-dependent terms are interpreted as new types of coupling between classical fields due to spacetime noncommutativity. We study how these perturbative NC corrections affect the field equations of motion and derive some phenomenological consequences, such as NC-deformed Landau levels of an electron. Finally, we discuss how topological gravity in four dimensions (both classical and noncommutative) appears as a low-energy sector of five-dimensional Chern-Simons gauge theory in the sense of Kaluza-Klein reduction.

hep-th↗

arXiv2023

Holographic Aspects of Even-Dimensional Topological Gravity

In an odd-dimensional spacetime, gravity can be formulated as a proper gauge theory based on the Chern-Simons action for a suitable gauge group. Performing dimensional reduction, one obtains, as an effective theory, Chamseddine's even-dimensional topological gravity with the reduced gauge symmetry. This theory involves a multiplet of scalar fields that appear as a result of the dimensional reduction, and it is topological in the sense that its action does not depend on the metric. Focusing primarily on the four-dimensional case, we use the holographic dictionary to compute one-point correlation functions of the relevant boundary operators and find that the spin-current can have a nonzero expectation value in the dual quantum field theory. We also consider the generalized holographic Weyl anomaly and find that it vanishes. Finally, we propose a way of computing two-point correlation functions using the gravitational Wilson lines.

hep-th↗

arXiv2022

Noncommutative $D=5$ Chern-Simons Gravity: Kaluza-Klein Reduction and Chiral Gravitational Anomaly

Actions for noncommutative (NC) gauge field theories can be expanded perturbatively in powers of the noncommutativity parameter $θ$ using the Seiberg-Witten map between ordinary classical fields and their NC counterparts. The leading order term represents classical ($θ=0$) action while higher-order terms give us $θ$-dependent NC corrections that ought to capture some aspects of quantum gravity. Building on previous work of Aschieri and Castellani on NC Chern-Simons (CS) gauge and gravity theories, showing that non-trivial $θ$-dependence exists only for spacetime dimensions $D\geq 5$, we investigate a correlated effect of these extra spatial dimensions and noncommutativity on four-dimensional physics, up to first-order in $θ$. Assuming that one spatial dimension is compactified into a circle, we apply the Kaluza-Klein reduction procedure on the NC $D=5$ CS theory for the conformal gauge group $SO(4,2)$, to obtain an effective, $θ$-dependent four-dimensional theory of gravity that has Einstein-Hilbert gravity with negative cosmological constant as its commutative limit. We derive field equations for this modified theory of gravity and study the effect of NC interactions on some classical geometries, such as the AdS-Schwarzschild black hole. We find that this NC background spacetime gives rise to chiral gravitational anomaly due to the nonvanishing $θ$-dependent Pontryagin density.

hep-th↗

arXiv2022

Page Curve for Eternal Schwarzschild Black Hole in Dimensionally-Reduced Model of Dilaton Gravity

As a contribution to the subject of the information loss paradox in (1+1)-dimensional gravitational systems, we study a model of (1+1)-dimensional dilaton gravity derived from the four-dimensional Einstein-Hilbert action by dimensional reduction. The reduced action involves the cosmological constant and admits black hole solutions. After including the back-reaction of quantum fields to 1-loop order, we solve the semi-classical field equations perturbatively and compute the quantum correction to the Hawking temperature. We consider the quantum extremal surface approach and invoke the ``island rule'' to compute the fine-grained entropy of the Hawking radiation for an eternal Schwarzschild black hole and demonstrate that it follows the unitary Page curve.

hep-th↗

arXiv2021

Microscopic derivation of Dirac composite fermion theory: Aspects of noncommutativity and pairing instabilities

Building on previous work [N. Read, Phys. Rev. B 58, Z. Dong and T. Senthil, 16262 (1998); Phys. Rev. B 102, 205126 (2020)] on the system of bosons at filling factor $ν= 1$, we derive the Dirac composite fermion theory for a half-filled Landau level from first principles and applying the Hartree-Fock approach in a preferred representation. On the basis of the microscopic formulation, in the long-wavelength limit, we propose a noncommutative field-theoretical description, which in a commutative limit reproduces the Son's theory, with additional terms that may be expected on physical grounds. The microscopic representation of the problem is also used to discuss pairing instabilities of composite fermions. We find that a presence of a particle-hole symmetry breaking leads to a weak (BCS) coupling $p$-wave pairing in the lowest Landau level, and strong coupling $p$-wave pairing in the second Landau level that occurs in a band with nearly flat dispersion, a third power function of momentum.

cond-mat.str-el↗

arXiv2021

Simulating indefinite causal order with Rindler observers

Realization of indefinite causal order (ICO), a theoretical possibility that even causal relations between physical events can be subjected to quantum superposition, apart from its general significance for the fundamental physics research, would also enable quantum information processing that outperforms protocols in which the underlying causal structure is definite. In this paper, we start with a proposition that an observer in a state of quantum superposition of being at two different relative distances from the event horizon of a black hole, effectively resides in ICO space-time generated by the black hole. By invoking the fact that the near-horizon geometry of a Schwarzschild black hole is that of a Rindler space-time, we propose a way to simulate an observer in ICO space-time by a Rindler observer in a state of superposition of having two different proper accelerations. By extension, a pair of Rindler observers with entangled proper accelerations simulates a pair of entangled ICO observers. Moreover, these Rindler-systems might have a plausible experimental realization by means of optomechanical resonators.

quant-ph↗

arXiv2020

Bell's theorem for trajectories

In classical theory, the trajectory of a particle is entirely predetermined by the complete set of initial conditions via dynamical laws. Based on this, we formulate a no-go theorem for the dynamics of classical particles, i.e., a Bell's inequality for trajectories, and discuss its possible violation in a quantum scenario. A trajectory, however, is not an outcome of a quantum measurement, in the sense that there is no observable associated with it, and thus there is no "direct" experimental test of the Bell's inequality for trajectories. Nevertheless, we show how to overcome this problem by considering a special case of our generic inequality that can be experimentally tested point-by-point in time. Such inequality is indeed violated by quantum mechanics, and the violation persists during an entire interval of time and not just at a particular singular instant. We interpret the violation to imply that trajectories (or at least pieces thereof) cannot exist predetermined, within a local-realistic theory.

quant-ph↗

arXiv2019

Canonical Deformation of $N=2$ $AdS_{4}$ SUGRA

It is known that one can define a consistent theory of extended, $N=2$ anti-de Sitter (AdS) Supergravity (SUGRA) in $D=4$. Besides the standard gravitational part, this theory involves a single $U(1)$ gauge field and a pair of Majorana vector-spinors that can be mixed into a pair of charged spin-$3/2$ gravitini. The action for $N=2$ $AdS_{4}$ SUGRA is invariant under $SO(1,3)\times U(1)$ gauge transformations, and under local SUSY. We present a geometric action that involves two "inhomogeneous" parts: an orthosymplectic $OSp(4\vert 2)$ gauge-invariant action of the Yang-Mills type, and a supplementary action invariant under purely bosonic $SO(2,3)\times U(1)\sim Sp(4)\times SO(2)$ sector of $OSp(4\vert 2)$, that needs to be added for consistency. This action reduces to $N=2$ $AdS_{4}$ SUGRA after gauge fixing, for which we use a constrained auxiliary field in the manner of Stelle and West. Canonical deformation is performed by using the Seiberg-Witten approach to noncommutative (NC) gauge field theory with the Moyal product. The NC-deformed action is expanded in powers of the deformation parameter $θ^{μν}$ up to the first order. We show that $N=2$ $AdS_{4}$ SUGRA has non-vanishing linear NC correction in the physical gauge, originating from the additional, purely bosonic action. For comparison, simple $N=1$ Poinacaré SUGRA can be obtained in the same manner, directly from an $OSp(4\vert 1)$ gauge-invariant action. The first non-vanishing NC correction is quadratic in $θ^{μν}$ and therefore exceedingly difficult to calculate. Under Wigner-Inönü (WI) contraction, $N=2$ AdS superalgebra reduces to $N=2$ Poincaré superalgebra, and it is not clear whether this relation holds after canonical deformation. We present the linear NC correction to $N=2$ $AdS_{4}$ SUGRA explicitly, discuss its low-energy limit, and what remains of it after WI contraction.

hep-th↗

arXiv2018

Noncommutative Electrodynamics from $SO(2,3)_\star$ Model of Noncommutative Gravity

In our previous work we have constructed a model of noncommutative (NC) gravity based on $SO(2,3)_\star$ gauge symmetry. In this paper we extend the model by adding matter fields: fermions and a $U(1)$ gauge field. Using the enveloping algebra approach and the Seiberg-Witten map we construct actions for these matter fields and expand the actions up to first order in the noncommutativity (deformation) parameter. Unlike in the case of pure NC gravity, first non-vanishing NC corrections are linear in the noncommutativity parameter. In the flat space-time limit we obtain a non-standard NC Electrodynamics. Finally, we discuss effects of noncommutativity on relativistic Landau levels of an electron in a constant background magnetic field and in addition we calculate the induced NC magnetic dipole moment of the electron.

hep-th↗

arXiv2017

Dirac field and gravity in NC $SO(2,3)_\star$ model

Action for the Dirac spinor field coupled to gravity on noncommutative (NC) Moyal-Weyl space-time is obtained without prior knowledge of the metric tensor. We emphasise gauge origins of gravity (i.e. metric structure) and its interaction with fermions by demonstrating that a classical action invariant under $SO(2,3)$ gauge transformations can be exactly reduced to the Dirac action in curved space-time after breaking the original symmetry down to the local Lorentz $SO(1,3)$ symmetry. The commutative, $SO(2,3)$ invariant action can be straightforwardly deformed via Moyal-Weyl $\star$-product to its NC $SO(2,3)_\star$ invariant version which can be expanded perturbatively in the powers of the deformation parameter using the Seiberg-Witten map. The gravity-matter couplings in the expansion arise as an effect of the gauge symmetry breaking. We calculate in detail the first order NC correction to the classical Dirac action in curved space-time and show that it does not vanish. This significant feature of the presented model enables us to potentially observe the NC effects already at the lowest perturbative order. Moreover, NC effects are apparent even in the flat space-time limit. We analyse NC modification of the Dirac equation, Feynman propagator and dispersion relation for electrons in Minkowski space-time.

hep-th↗