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C. Farina

Publications and source records attributed to C. Farina.

At least 109 records · Page 6Linked to original sources
arXiv2000

A Simple Model for the Non-Retarded Dispersive Force between an Electrically Polarizable Atom and a Magnetic Polarizable One

It is well known that for the case of two neutral but electrically polarizable atoms the consideration or not of retardation effects on the dispersive van der Waals force between them leads essentially to different power laws for the forces; while the retarded force is proportional to $1/r^8$, where $r$ is the distance between the atoms, the non-retarded force is proportional to $1/r^7$. Here we consider the (repulsive) dispersive force between an electrically polarizable atom and a magnetically polarizable one and show that, in contrast to the previous case, a quite unexpected result appears, namely: while the retarded force is still proportional to $1/r^8$, the non-retarded force is proportional to $1/r^5$. We employ a semiclassical method based on the fluctuating dipole model for both atoms.

physics.atom-ph↗
arXiv2000

The non-retarded dispersive force between an electrically polarizable atom and a magnetically polarizable one

Using perturbative QED we show that, while the retarded dispersive force between an electrically polarizable atom and a magnetically polarizable one is proportional to $1/r^{8}$, where $r$ is the distance between the atoms, the non-retarded force is proportiaonal to $1/r^{5}$. This is a rather surprising result that should be compared with the dispersive van der Waals force between two electrically polarizable atoms, where the retarded force is also proportional to $1/r^{8}$, but the non-retarded force is proportional to $1/r^{7}$.

hep-th↗
arXiv1999

Spontaneous emission between an unusual pair of plates

We compute the modification in the spontaneous emission rate for a two-level atom when it is located between two parallel plates of different nature: a perfectly conducting plate $(ε\to \infty)$ and an infinitely permeable one $(μ\to \infty)$. We also discuss the case of two infinitely permeable plates. We compare our results with those found in the literature for the case of two perfectly conducting plates.

quant-ph↗
arXiv1999

Magnetic permeability of constrained scalar QED vacuum

We compute the influence of boundary conditions on the Euler-Heisenberg effective Lagrangian scalar QED scalar for the case of a pure magnetic field. The boundary conditions constrain the quantum scalar field to vanish on two parallel planes separeted by a distance $a$ and the magnetic field is assumed to be constant, uniform and perpendicular to the planes. The effective Lagrangian is obtained using Schwinger's proper-time representation and exhibits new contributions generated by the boundary condition much in the same way as a material pressed between two plates exhibits new magnetic properties. The confined bosonic vacuum presents the expected diamagnetic properties and besides the new non-linear $a$-dependent contributions to the susceptibility we show that there exists also a new $a$-dependent contribution for the vacuum permeability in the linear approximation.

hep-th↗
arXiv1999

Bosonic Casimir effect in external magnetic field

We compute the influence of an external magnetic field on the Casimir energy of a massive charged scalar field confined between two parallel infinite plates. For this case the obtained result shows that the magnetic field inhibits the Casimir effect.

hep-th↗
arXiv1998

Quasiperiodic fields and Bose-Einstein condensation

We construct a partition function for fields obeying a quasiperiodic boundary condition at finite temperature, $ψ(0;\vec x)= e^{iθ} ψ(β;\vec x)$, which interpolate continously that ones corresponding to bosons and fermions and discuss the possibility of condensation for these fields.

hep-th↗
arXiv1998

Generalized partition functions, interpolating statistics and higher virial coefficients

Starting from determinants at finite temperature obeying an intermediate boundary condition between the periodic (bosonic) and antiperiodic (fermionic) cases, we find results which can be mapped onto the ones obtained from anyons for the second virial coefficient. Using this approach, we calculate the corresponding higher virial coefficients and compare them with the results known in the literature.

hep-th↗
arXiv1998

Magnetic properties of confined bosonic vacuum at finite temperature

We compute the combined effect of confinement, an external magnetic field and temperature on the vacuum of the charged scalar field using Schwinger's formula for the effective action in the imaginary time formalism. The final result reproduces an effective Lagrangian similar to the Heisenberg-Euler one in the limit of no confinement, in the case of confinement it provides the necessary corrections to this Lagrangian at each order of magnitude of the magnetic field. The results show a finite temperature contribution to the vacum permeability constant apart from the one due to confinement alone.

hep-th↗
arXiv1998

QED vacuum between an unusual pair of plates

We consider the photon field between an unusual configuration of infinite parallel plates: a perfectly conducting plate $(ε\to\infty)$ and an infinitely permeable one $μ\to\infty)$. After quantizing the vector potential in the Coulomb gauge, we obtain explicit expressions for the vacuum expectation values of field operators of the form $<{\hat E}_i{\hat E}_j>_0$ and $<{\hat B}_i{\hat B}_j>_0$. These field correlators allow us to reobtain the Casimir effect for this set up and to discuss the light velocity shift caused by the presence of plates (Scharnhorst effect \cite{Scharnhorst,Barton,BarScharn}) for both scalar and spinor QED.

hep-th↗
arXiv1998

Casimir effect at finite temperature of charged scalar field

The Casimir effect for Dirac as well as for scalar charged particles is influenced by external magnetic fields. It is also influenced by finite temperature. Here we consider the Casimir effect for a charged scalar field under the combined influence of an external magnetic field and finite temperature. The free energy for such a system is computed using Schwinger's method for the calculation of the effective action in the imaginary time formalism. We consider both the limits of strong and weak magnetic field in which we compute the Casimir free energy and pressure.

hep-th↗
arXiv1998

Fermionic Casimir effect in an external magnetic field

The influence of an external constant uniform magnetic field on the Casimir energy density of a Dirac field under antiperiodic (and periodic) boundary condition is computed by applying Schwinger's proper time method. The result thus obtained shows that in principle, under suitable conditions, the magnetic field can enhance the fermionic Casimir energy density.

hep-th↗
arXiv1998

Magnetic Permeability of Constrained Fermionic Vacuum

We obtain using Schwinger's proper time approach the Casimir-Euler-Heisenberg effective action of fermion fluctuations for the case of an applied magnetic field. We implement here the compactification of one space dimension into a circle through anti-periodic boundary condition. Aside of higher order non-linear field effects we identify a novel contribution to the vacuum permeability. These contributions are exceedingly small for normal electromagnetism due to the smallness of the electron Compton wavelength compared to the size of the compactified dimension, if we take the latter as the typical size of laboratory cavities, but their presence is thought provoking, also considering the context of strong interactions.

hep-th↗
arXiv1998

Generalized partition functions and interpolating statistics

We show that the assumption of quasiperiodic boundary conditions (those that interpolate continuously periodic and antiperiodic conditions) in order to compute partition functions of relativistic particles in 2+1 space-time can be related with anyonic physics. In particular, in the low temperature limit, our result leads to the well known second virial coefficient for anyons. Besides, we also obtain the high temperature limit as well as the full temperature dependence of this coefficient.

hep-th↗
arXiv1995

GENERALIZED THERMAL ZETA-FUNCTIONS

We calculate the partition function of a harmonic oscillator with quasi-periodic boundary conditions using the zeta-function method. This work generalizes a previous one by Gibbons and contains the usual bosonic and fermionic oscillators as particular cases. We give an alternative prescription for the analytic extension of the generalized Epstein function involved in the calculation of the generalized thermal zeta-functions. We also conjecture about the relation of our calculation to anyonic systems.

hep-th↗
arXiv1994

The Partition Function for an Anyon-Like Oscillator

We compute the partition function of an anyon-like harmonic oscillator. The well known results for both the bosonic and fermionic oscillators are then reobtained as particular cases as ours. The technique we employ is a non-relativistic version of the Green function method used in the computation of one-loop effective actions of quantum field theory.

hep-th↗
arXiv1994

Schwinger's Method for the Massive Casimir Effect

We apply to the massive scalar field a method recently proposed by Schwinger to calculate the Casimir effect. The method is applied with two different regularization schemes: the Schwinger original one by means of Poisson formula and another one by means of analytical continuation.

hep-th↗