636 research outputs found
Testing Born-Infeld electrodynamics in waveguides
Waveguides can be employed to test non-linear effects in electrodynamics. We
solve Born-Infeld equations for TE waves in a rectangular waveguide. We show
that the energy velocity acquires a dependence on the amplitude, and harmonic
components appear as a consequence of the non-linear behavior.Comment: 3 pages. To appear in PR
The Classical Relativistic Quark Model in the Rest-Frame Wigner-Covariant Coulomb Gauge
The system of N scalar particles with Grassmann-valued color charges plus the
color SU(3) Yang-Mills field is reformulated on spacelike hypersurfaces. The
Dirac observables are found and the physical invariant mass of the system in
the Wigner-covariant rest-frame instant form of dynamics (covariant Coulomb
gauge) is given. From the reduced Hamilton equations we extract the second
order equations of motion both for the reduced transverse color field and the
particles. Then, we study this relativistic scalar quark model, deduced from
the classical QCD Lagrangian and with the color field present, in the N=2
(meson) case. A special form of the requirement of having only color singlets,
suited for a field-independent quark model, produces a ``pseudoclassical
asymptotic freedom" and a regularization of the quark self-energy.Comment: 81 pages, RevTe
Non-Newtonian Mechanics
The classical motion of spinning particles can be described without employing
Grassmann variables or Clifford algebras, but simply by generalizing the usual
spinless theory. We only assume the invariance with respect to the Poincare'
group; and only requiring the conservation of the linear and angular momenta we
derive the zitterbewegung: namely the decomposition of the 4-velocity in the
newtonian constant term p/m and in a non-newtonian time-oscillating spacelike
term. Consequently, free classical particles do not obey, in general, the
Principle of Inertia. Superluminal motions are also allowed, without violating
Special Relativity, provided that the energy-momentum moves along the worldline
of the center-of-mass. Moreover, a non-linear, non-constant relation holds
between the time durations measured in different reference frames. Newtonian
Mechanics is re-obtained as a particular case of the present theory: namely for
spinless systems with no zitterbewegung. Introducing a Lagrangian containing
also derivatives of the 4-velocity we get a new equation of the motion,
actually a generalization of the Newton Law a=F/m. Requiring the rotational
symmetry and the reparametrization invariance we derive the classical spin
vector and the conserved scalar Hamiltonian, respectively. We derive also the
classical Dirac spin and analyze the general solution of the Eulero-Lagrange
equation for Dirac particles. The interesting case of spinning systems with
zero intrinsic angular momentum is also studied.Comment: LaTeX; 27 page
The quantum algebra of superspace
We present the complete set of , quantum algebras associated to
massive superparticles. We obtain the explicit solution of these algebras
realized in terms of unconstrained operators acting on the Hilbert space of
superfields. These solutions are expressed using the chiral, anti-chiral and
tensorial projectors which define the three irreducible representations of the
supersymmetry on the superfields. In each case the space-time variables are
non-commuting and their commutators are proportional to the internal angular
momentum of the representation. The quantum algebra associated to the chiral or
the anti-chiral projector is the one obtained by the quantization of the
Casalbuoni-Brink-Schwarz (superspin 0) massive superparticle. We present a new
superparticle action for the (superspin 1/2) case and show that their wave
functions are the ones associated to the irreducible tensor multiplet.Comment: 20 pages;changes in the nomenclatur
Effective field theories for QED bound states: extending Nonrelativistic QED to study retardation effects
Nonrelativistic QED bound states are difficult to study because of the
presence of at least three widely different scales: the masses, three-momenta
() and kinetic energies () of the constituents. Nonrelativistic QED
(NRQED), an effective field theory developed by Caswell and Lepage, simplifies
greatly bound state calculations by eliminating the masses as dynamical scales.
As we demonstrate, NRQED diagrams involving only photons of energy contribute, in any calculation, to a unique order in . This
is not the case, however, for diagrams involving photons with energies
(``retardation effects"), for which no simple counting
counting rules can be given. We present a new effective field theory in which
the contribution of those ultra-soft photons can be isolated order by order in
. This is effectively accomplished by performing a multipole expansion
of the NRQED vertices.Comment: 39 pages, 9 Postscript figures, uses Rev.tex V3.0 and epsf.te
Post-Newtonian accurate parametric solution to the dynamics of spinning compact binaries in eccentric orbits: The leading order spin-orbit interaction
We derive Keplerian-type parametrization for the solution of post-Newtonian
(PN) accurate conservative dynamics of spinning compact binaries moving in
eccentric orbits. The PN accurate dynamics that we consider consists of the
third post-Newtonian accurate conservative orbital dynamics influenced by the
leading order spin effects, namely the leading order spin-orbit interactions.
The orbital elements of the representation are explicitly given in terms of the
conserved orbital energy, angular momentum and a quantity that characterizes
the leading order spin-orbit interactions in Arnowitt, Deser, and Misner-type
coordinates. Our parametric solution is applicable in the following two
distinct cases: (i) the binary consists of equal mass compact objects, having
two arbitrary spins, and (ii) the binary consists of compact objects of
arbitrary mass, where only one of them is spinning with an arbitrary spin. As
an application of our parametrization, we present gravitational wave
polarizations, whose amplitudes are restricted to the leading quadrupolar
order, suitable to describe gravitational radiation from spinning compact
binaries moving in eccentric orbits. The present parametrization will be
required to construct `ready to use' reference templates for gravitational
waves from spinning compact binaries in inspiralling eccentric orbits. Our
parametric solution for the post-Newtonian accurate conservative dynamics of
spinning compact binaries clearly indicates, for the cases considered, the
absence of chaos in these systems. Finally, we note that our parametrization
provides the first step in deriving a fully second post-Newtonian accurate
`timing formula', that may be useful for the radio observations of relativistic
binary pulsars like J0737-3039.Comment: 18 pages, accepted by Phys. Rev.
The Kepler equation for inspiralling compact binaries
Compact binaries consisting of neutron stars / black holes on eccentric orbit
undergo a perturbed Keplerian motion. The perturbations are either of
relativistic origin or are related to the spin, mass quadrupole and magnetic
dipole moments of the binary components. The post-Newtonian motion of such
systems decouples into radial and angular parts. We present here for the first
time the radial motion of such a binary encoded in a generalized Kepler
equation, with the inclusion of all above-mentioned contributions, up to linear
order in the perturbations. Together with suitably introduced parametrizations,
the radial motion is solved completely
Direct perturbation theory on the shift of Electron Spin Resonance
We formulate a direct and systematic perturbation theory on the shift of the
main paramagnetic peak in Electron Spin Resonance, and derive a general
expression up to second order. It is applied to one-dimensional XXZ and
transverse Ising models in the high field limit, to obtain explicit results
including the polarization dependence for arbitrary temperature.Comment: 5 pages (no figures) in REVTE
Classical String in Curved Backgrounds
The Mathisson-Papapetrou method is originally used for derivation of the
particle world line equation from the covariant conservation of its
stress-energy tensor. We generalize this method to extended objects, such as a
string. Without specifying the type of matter the string is made of, we obtain
both the equations of motion and boundary conditions of the string. The world
sheet equations turn out to be more general than the familiar minimal surface
equations. In particular, they depend on the internal structure of the string.
The relevant cases are classified by examining canonical forms of the effective
2-dimensional stress-energy tensor. The case of homogeneously distributed
matter with the tension that equals its mass density is shown to define the
familiar Nambu-Goto dynamics. The other three cases include physically relevant
massive and massless strings, and unphysical tahyonic strings.Comment: 12 pages, REVTeX 4. Added a note and one referenc
Image restoration using the chiral Potts spin-glass
We report on the image reconstruction (IR) problem by making use of the
random chiral q-state Potts model, whose Hamiltonian possesses the same gauge
invariance as the usual Ising spin glass model. We show that the pixel
representation by means of the Potts variables is suitable for the gray-scale
level image which can not be represented by the Ising model. We find that the
IR quality is highly improved by the presence of a glassy term, besides the
usual ferromagnetic term under random external fields, as very recently pointed
out by Nishimori and Wong. We give the exact solution of the infinite range
model with q=3, the three gray-scale level case. In order to check our
analytical result and the efficiency of our model, 2D Monte Carlo simulations
have been carried out on real-world pictures with three and eight gray-scale
levels.Comment: RevTex 13 pages, 10 figure
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