2,847 research outputs found
Pseudoclassical theories of Majorana, Weyl and Majorana--Weyl particles
A pseudoclassical theories of Majorana, Weyl and Majorana--Weyl particles in
the space--time dimensions are constructed. The canonical quantization
of these theories is carried out and as a result we obtain the quantum
mechanical description of neutral particle in , Weyl particle in
and neutral Weyl particle in . In dimensional
space--time the description of the neutral particle coincides with the field
theoretical description of the Majorana particle in the Foldy--Wouthuysen
representation. In dimensions the neutral Weyl particle coincides with
the Majorana--Weyl particle in the Foldy--Wouthuysen representation.Comment: LATEX, 17 pages, no figure
Structure of Vector Mesons in Holographic Model with Linear Confinement
Wave functions and form factors of vector mesons are investigated in the
holographic dual model of QCD with a smooth oscillator-like wall. We introduce
wave functions conjugate to solutions of the 5D equation of motion and develop
a formalism based on these wave functions, which are very similar to those of a
quantum-mechanical oscillator. For the lowest bound state (rho-meson), we show
that, in this model, the basic elastic form factor exhibits the perfect vector
meson dominance, i.e., it is given by the rho-pole contribution alone. The
electric radius of the rho-meson is calculated, _C = 0.655 fm^2, which
is larger than in case of the hard-wall cutoff. The squared radii of higher
excited states are found to increase logarithmically rather than linearly with
the radial excitation number. We calculate the coupling constant f_rho and find
that the experimental value is closer to that calculated in the hard-wall
model.Comment: 8 pages, RevTex4, references, comments and a figure added. Some
terminoloy change
Isometric Representations of Totally Ordered Semigroups
Let S be a subsemigroup of an abelian torsion-free group G. If S is a
positive cone of G, then all C*-algebras generated by faithful isometrical
non-unitary representations of S are canonically isomorphic. Proved by Murphy,
this statement generalized the well-known theorems of Coburn and Douglas. In
this note we prove the reverse. If all C*-algebras generated by faithful
isometrical non-unitary representations of S are canonically isomorphic, then S
is a positive cone of G. Also we consider G = Z\times Z and prove that if S
induces total order on G, then there exist at least two unitarily not
equivalent irreducible isometrical representation of S. And if the order is
lexicographical-product order, then all such representations are unitarily
equivalent.Comment: February 21, 2012. Kazan, Russi
Self-amplified Cherenkov radiation from a relativistic electron in a waveguide partially filled with a laminated material
The radiation from a relativistic electron uniformly moving along the axis of
cylindrical waveguide filled with laminated material of finite length is
investigated. Expressions for the spectral distribution of radiation passing
throw the transverse section of waveguide at large distances from the laminated
material are derived with no limitations on the amplitude and variation profile
of the layered medium permittivity and permeability. Numerical results for
layered material consisting of dielectric plates alternated with vacuum gaps
are given. It is shown that at a special choice of problem parameters,
Cherenkov radiation generated by the relativistic electron inside the plates is
self-amplified. The visual explanation of this effect is given and a possible
application is discussed.Comment: 8 pages, 4 figures,1 table, the paper is accepted for publication in
the Journal of Physics: Conference Serie
Synchrotron radiation from a charge moving along a helical orbit inside a dielectric cylinder
The radiation emitted by a charged particle moving along a helical orbit
inside a dielectric cylinder immersed into a homogeneous medium is
investigated. Expressions are derived for the electromagnetic potentials,
electric and magnetic fields, and for the spectral-angular distribution of
radiation in the exterior medium. It is shown that under the Cherenkov
condition for dielectric permittivity of the cylinder and the velocity of the
particle image on the cylinder surface, strong narrow peaks are present in the
angular distribution for the number of radiated quanta. At these peaks the
radiated energy exceeds the corresponding quantity for a homogeneous medium by
some orders of magnitude. The results of numerical calculations for the angular
distribution of radiated quanta are presented and they are compared with the
corresponding quantities for radiation in a homogeneous medium. The special
case of relativistic charged particle motion along the direction of the
cylinder axis with non-relativistic transverse velocity (helical undulator) is
considered in detail. Various regimes for the undulator parameter are
discussed. It is shown that the presence of the cylinder can increase
essentially the radiation intensity.Comment: 18 pages, 8 EPS figure
On the influence of acoustic waves on coherent bremsstrahlung in crystals
We investigate the coherent bremsstrahlung by relativistic electrons in a
single crystal excited by hypersonic vibrations. The formula for the
corresponding differential cross-section is derived in the case of a sinusoidal
wave. The conditions are specified under which the influence of the hypersound
is essential. The case is considered in detail when the electron enters into
the crystal at small angles with respect to a crystallographic axis. It is
shown that in dependence of the parameters, the presence of hypersonic waves
can either enhance or reduce the bremsstrahlung cross-section.Comment: 11 pages, 6 EPS figures, LaTe
Analyticity, Unitarity and One-loop Graviton Corrections to Compton Scattering
We compute spin-flip cross section for graviton photoproduction on a spin-1/2
target of finite mass. Using this tree-level result, we find one-loop graviton
correction to the spin-flip low-energy forward Compton scattering amplitude by
using Gerasimov-Drell-Hearn sum rule. We show that this result agrees with the
corresponding perturbative computations, implying the validity of the sum rule
at one-loop level, contrary to the previous claims. We discuss possible effects
from the black hole production and string Regge trajectory exchange at very
high energies. These effects seem to soften the UV divergence present at
one-loop graviton level. Finally, we discuss the relation of these observations
with the models that involve extra dimensions.Comment: 15 pages, 3 figure
Pion Form Factor in Chiral Limit of Hard-Wall AdS/QCD Model
We develop a formalism to calculate form factor and charge density
distribution of pion in the chiral limit using the holographic dual model of
QCD with hard-wall cutoff. We introduce two conjugate pion wave functions and
present analytic expressions for these functions and for the pion form factor.
They allow to relate such observables as the pion decay constant and the pion
charge electric radius to the values of chiral condensate and hard-wall cutoff
scale. The evolution of the pion form factor to large values of the momentum
transfer is discussed, and results are compared to existing experimental data.Comment: 21 page, 7 figures. Short comparison with NJL predictions for pion
radius and new references added. To be published in Phys.Rev.
Towards the Gravity Dual of Quarkonium in the Strongly Coupled QCD Plasma
We build a "bottom-up" holographic model of charmonium by matching the
essential spectral data. We argue that this data must include not only the
masses but also the decay constants of the J/psi and psi' mesons. Relative to
the "soft-wall" models for light mesons, such a matching requires two new
features in the holographic potential: an overall upward shift as well as a
narrow "dip" near the holographic boundary. We calculate the spectral function
as well as the position of the complex singularities (quasinormal frequencies)
of the retarded correlator of the charm current at finite temperatures. We
further extend this analysis by showing that the residues associated with these
singularities are given by the boundary derivative of the appropriately
normalized quasinormal mode. We find that the "melting" of the J/psi spectral
peak occurs at a temperature of about 540 MeV, or 2.8 T_c, in good agreement
with lattice results.Comment: 13 pages, 9 figure
- …