arXiv subjects

Ion V. Vancea

Publications and source records attributed to Ion V. Vancea.

At least 19 recordsLinked to original sources

arXiv2024

Fractional Particle and Sigma Model

We introduce a classical fractional particle model in $\mathbb{R}^{n}$, extending the Newtonian particle concept with the incorporation of the fractional Laplacian. A comprehensive discussion on kinetic properties, including linear momentum and kinetic energy, is provided. We further derive the equations of motion and discuss the symmetries of the system. The Green's function method is employed to solve the equations of motion in a general case. We illustrate the theory with three important examples: the free fractional particle, the fractional harmonic oscillator, and the charged fractional particle that interacts locally with the electromagnetic field. We use the results of the extension problem by Caffarelli and Silvestre, to construct the associated classical local sigma model for the fractional particle. The sigma model is then quantized using the canonical quantization method, and we compute the vacuum energy at the boundary.

hep-th↗

arXiv2021

Classical boundary field theory of Jacobi sigma models by Poissonization

In this paper, we are going to construct the classical field theory on the boundary of the embedding of $\mathbb{R} \times S^{1}$ into the manifold $M$ by the Jacobi sigma model. By applying the poissonization procedure and by generalizing the known method for Poisson sigma models, we express the fields of the model as perturbative expansions in terms of the reduced phase space of the boundary. We calculate these fields up to the second order and illustrate the procedure for contact manifolds.

hep-th↗

arXiv2020

Nonlinear dynamics of a charged particle in a strong non-null knot wave background

In this paper, we study the dynamics of the charged particle interacting with the non-null electromagnetic knot wave background. We analyse the classical system in the Hamilton-Jacobi formalism and find the action, the linear momentum and the trajectory of the particle. Also, we calculate the effective mass and the emitted radiation along the knot wave. Next, we quantize the system in the classical strong knot wave background by using the strong-field QED canonical formalism. We explicitly construct the Furry picture and calculate the Volkov solutions of the Dirac equation. As an application, we discuss the one-photon Compton effect where we determine the general form of the $S$-matrix. Also, we discuss in details the first partial amplitudes in the transition matrix in two simple backgrounds and show that there is a pair of states for which these amplitudes are identical.

hep-th↗

arXiv2020

Finsler Geometries from Topological Electromagnetism

We analyse the Finsler geometries of the kinematic space of spinless and spinning electrically charged particles in an external Rañada field. We consider the most general actions that are invariant under the Lorentz, electromagnetic gauge and reparametrization transformations. The Finsler geometries form a set parametrized by the gauge fields in each case. We give a simple method to calculate the fundamental objects of the Finsler geometry of the kinematic space of a particle in a generic electromagnetic field. Then we apply this method to calculate the geodesic equations of the spinless and spinning particles. Also, we show that the electromagnetic duality in the Rañada background induces a simple dual map in the set of Finsler geometries. The duality map has a simple interpretation in terms of an electrically charged particle that interacts with the electromagnetic potential and a magnetically charged particle that interacts with the dual magnetoelectric potential. We exemplify the action of the duality map by calculating the dual geodesic equation.

hep-th↗

arXiv2020

Knots and the Maxwell Equations

In this chapter, we review the Rañada field line solutions of Maxwell's equations in the vacuum, which describe a topologically non-trivial electromagnetic field, as well as their relation with the knot theory. Also, we present a generalization of these solutions to the non-linear electrodynamics recently published in the literature.

physics.class-ph↗

arXiv2020

Field Line Solutions of the Einstein-Maxwell Equations

In this paper, we are going to review the gravitating electromagnetic field in the 1+3 formalism on a general hyperbolic space-time manifold. We also discuss the recent results on the existence of the local field line solutions of the Einstein-Maxwell equations that generalize the Rañada solutions from the flat space-time. The global field line solutions do not always exist since the space-time manifold could impose obstructions to the global extension of various geometric objects necessary to build the fields. One example of a gravitating field line solution is the Kopiński-Natário field which is discussed in some detail.

gr-qc↗

arXiv2019

Backreaction of particle production on physical gravitons in the de Sitter space

We derive the effects of the scalar particle production on the physical graviton operator in the de Sitter space. Our analysis is done for the sub-horizon modes at large values of the conformal time. In this limit, we completely determine the correction to the scalar energy-momentum tensor at the first order in the WKB iteration. Also, we calculate the corresponding correction to the graviton operator for a single sub-horizon mode.

hep-th↗

arXiv2019

Graviton spectrum in simplified Dark Matter models with graviton mediators in the de Sitter space

This is the second in a series of papers investigating the formulation of the simplified Dark Matter models with graviton mediators in cosmological backgrounds. We address here the crucial problem of the fundamental observable of interest, namely the graviton spectrum in a FRW cosmological background with an arbitrary Dark Matter background component. We calculate the correction to the free graviton two-point function up to the second order in the coupling constant between the Dark Matter and the graviton in the simplified Dark Matter model with graviton mediators approach in the de Sitter space. Our result is model independent in the sense that it does not depend on the particular form of the Dark Matter fields. Also, due to the universality of the interaction between the Dark Matter and the graviton, the result obtained here apply to the interaction between the baryonic matter and the gravitons. As an application, we discuss in detail the massive scalar Dark Matter model and calculate the first order correction to the two-point function due to two Dark Matter modes in the adiabatic regime.

gr-qc↗

arXiv2018

Gravity-mediated Dark Matter models in the de Sitter space

In this paper, we generalize the simplified Dark Matter models with graviton mediator to the curved space-time, in particular to the de Sitter space. We obtain the generating functional of the Green's functions in the Euclidean de Sitter space for the covariant free gravitons. We determine the generating functional of the interacting theory between Dark Matter particles and the covariant gravitons. Also, we calculate explicitly the 2-point and 3-point interacting Green's functions for the symmetric traceless divergence-less covariant graviton. The results derived here are general in the sense that they do not depend on a particular model for the Dark Matter component and they show that the quantum effects of the interaction between the Dark Matter and the gravitons in the de Sitter space are computable by the methods of the standard Quantum Field Theory techniques.

hep-th↗

arXiv2017

On the existence of the field line solutions of the Einstein-Maxwell equations

The main result of this paper is the proof that there are local electric and magnetic field configurations expressed in terms of field lines on an arbitrary hyperbolic manifold. This electromagnetic field is described by (dual) solutions of the Maxwell's equations of the Einstein-Maxwell theory. These solutions have the following important properties: i) they are general, in the sense that the knot solutions are particular cases of them and ii) they reduce to the electromagnetic fields in the field line representation in the flat space-time. Also, we discuss briefly the real representation of these electromagnetic configurations and write down the corresponding Einstein equations.

gr-qc↗

arXiv2017

Entanglement Entropy in the $σ$-Model with the de Sitter Target Space

We derive the formula of the entanglement entropy between the left and right oscillating modes of the $σ$-model with the de Sitter target space. To this end, we study the theory in the \emph{cosmological gauge} in which the non-vanishing components of the metric on the two-dimensional base space are functions of the expansion parameter of the de Sitter space. The model is embedded in the causal north pole diamond of the Penrose diagram. We argue that the cosmological gauge is natural to the $σ$-model as it is compatible with the canonical quantization relations. In this gauge, we obtain a new general solution to the equations of motion in terms of time-independent oscillating modes. The constraint structure is adequate for quantization in the Gupta-Bleuler formalism. We construct the space of states as a one-parameter family of Hilbert spaces and give the Bargmann-Fock and Jordan-Schwinger representations of it. Also, we give a simple description of the physical subspace as an infinite product of $\mathcal{D}^{+}_{\frac{1}{2}}$ in the positive discreet series irreducible representations of the $SU(1,1)$ group. We construct the map generated by the Hamiltonian between states at two different values of time and show how it produces the entanglement of left and right excitations. Next, we derive the formula of the entanglement entropy of the reduced density matrix for the ground state acted upon by the Hamiltonian map. Finally, we determine the asymptotic form of the entanglement entropy of a single mode bi-oscillator in the limit of large values of time.

hep-th↗

arXiv2017

Nonequilibrium dynamics of the $σ$-model modes on the de Sitter space

The two-dimensional $σ$-model with the de Sitter target space has a local canonical description in the north pole diamond of the Penrose diagram in the cosmological gauge. The left and right moving modes on the embedded base space with the topology of a cylinder are entangled among themselves and interact with the time-dependent components of the metric of the de Sitter space. Firstly we address the issue of the existence of the untangled oscillator representation and the description of the nonequilibrium dynamics of the untangled modes. We show that the untangled oscillators can be obtained from the entangled operators by applying a set of Bogoliubov transformations that satisfy a set of constraints that result from the requirement that the partial evolution generator be diagonal. Secondly, we determine the nonequilibrium dynamics of the untangled modes in the Non-Equilibrium Thermo Field Dynamics formalism. In this setting, the thermal modes are represented as thermal doublet oscillators that satisfy partial evolution equations of Heisenberg-type. We use these equations to compute the local free one-body propagator of an arbitrary mode between two times. Thirdly, we discuss the field representation of the thermal modes. We show that there is a set of thermal doublet fields that satisfy the equal time canonical commutation relations, are solutions to the $σ$-model equations of motion and can be decomposed in terms of thermal doublet oscillators. Finally, we construct a local partial evolution functional of Hamilton-like form for the thermal doublet fields.

hep-th↗

arXiv2015

Thermo Field Dynamics of strings with definite boundary conditions

In this paper we review the construction of the thermal bosonic string and $D$-brane in the framework of the Thermo Field Dynamics (TFD). We briefly recall the well-known light-cone quantization of the bosonic string in the conformal gauge in flat space-time. Then we give a bird's eye view of the fundamental concepts of the TFD. Also, we present the thermalization of the bosonic string and the construction of the thermal D-brane boundary state. Finally, we show the calculation of the entropy of the thermal open string states with all boundary conditions and the entropy of the thermal D-brane state.

hep-th↗

arXiv2008

On the Dirac Eigenvalues as Observables of the on-shell N=2 D=4 Euclidean Supergravity

We generalize previous works on the Dirac eigenvalues as dynamical variables of the Euclidean gravity and N=1 D=4 supergravity to on-shell N=2 D=4 Euclidean supergravity. The covariant phase space of the theory is defined as as the space of the solutions of the equations of motion modulo the on-shell gauge transformations. In this space we define the Poisson brackets and compute their value for the Dirac eigenvalues.

hep-th↗

arXiv2008

Semiclassical bosonic D-brane boundary states in curved spacetime

We give a simple method to calculate the semiclassical $D$-brane boundary states of the bosonic string propagating in an arbitrary curved spacetime in a perturbative approach in which the metric $g_{AB}$ and the constant antisymmetric Kalb-Ramond field $b_{AB}$ form the general background which is treated exactly. As an important particular case, it is shown that at the first order perturbation theory there are $D$-brane coherent states in the $d$-dimensional {\em AdS} spacetime if certain conditions are fulfilled by the boundary projectors.

hep-th↗

arXiv2008

Thermal D-brane boundary states from type IIB Green-Schwarz superstring in pp-wave background

We construct the thermal boundary states from the type IIB Green-Schwarz superstring in {\em pp}-wave background in the light-cone gauge. The superstring is treated in the canonical ensemble and in the TFD formalism which is appropriate to discuss quantum systems in the canonical quantization. The thermal boundary states are obtained by thermalizing the total boundary states which are the boundary states of the total system that is composed by the superstring modes and the corresponding thermal reservoir modes. That analysis is similar to the one in the flat spacetime case \cite{ivv12}. However, there are some subtleties concerning the construction of the total string which are discussed. Next, we compute the entropy of thermal boundary state which is defined as the expectation value of the superstring entropy operator in the thermal boundary state.

hep-th↗

arXiv2006

Thermal D-branes States from Superstrings in Light-Cone Gauge

In this talk we are going to review a method to construct the thermal boundary states of the thermal string in the TFD approach. The class of thermal boundary states presented here is derived from the BPS D-branes of the type II GS superstrings.

hep-th↗

arXiv2006

Thermal $D$-Brane Boundary States from Green-Schwarz Superstrings

In this paper we thermalize the type II superstrings in the GS formulation by applying the TFD formalism. The thermal boundary conditions on the thermal Hilbert space are obtained from the BPS $D$-brane boundary conditions at zero temperature. We show that thermal boundary states can be obtained by thermalization from the BPS $D$-branes at zero temperature. These new states can be interpreted as thermal $D$-branes. Next, we discuss the supersymmetry breaking of the thermal string in the TFD approach. We identify the broken supersymmetry with the $ε$-transformation while the $η$-transformation is preserved. Also, we compute the thermal partition function and the entropy of the thermal string.

hep-th↗