2,256 research outputs found
Optical amplification enhancement in photonic crystals
Improving and controlling the efficiency of a gain medium is one of the most
challenging problems of laser research. By measuring the gain length in an opal
based photonic crystal doped with laser dye, we demonstrate that optical
amplification is more than twenty-fold enhanced along the Gamma-K symmetry
directions of the face centered cubic photonic crystal. These results are
theoretically explained by directional variations of the density of states,
providing a quantitative connection between density of the states and light
amplification
Mass singularity and confining property in
We discuss the properties of the position space fermion propagator in three
dimensional QED which has been found previouly based on Ward-Takahashi-identity
for soft-photon emission vertex and spectral representation.There is a new type
of mass singularity which governs the long distance behaviour.It leads the
propagator vanish at large distance.This term corresponds to dynamical mass in
position space.Our model shows confining property and dynamical mass generation
for arbitrary coupling constant.Since we used dispersion retation in deriving
spectral function there is a physical mass which sets a mass scale.For finite
cut off we obtain the full propagator in the dispersion integral as a
superposition of different massses.Low energy behaviour of the proagator is
modified to decrease by position dependent mass.In the limit of zero infrared
cut-off the propagator vanishes with a new kind of infrared behaviour.Comment: 22pages,4figures,revtex4,Notational sloppiness are crrected.Submitted
to JHE
Superstring-Inspired E_6 Unification, Shadow Theta-Particles and Cosmology
We construct a new cosmological model considering the superstring-inspired
E_6 unification in the 4-dimensional space at the early stage of the Universe.
We develop a concept of parallel existence in Nature of the ordinary and shadow
worlds with different cosmological evolutions.Comment: 7 page
Superfield Approach to (Non-)local Symmetries for One-Form Abelian Gauge Theory
We exploit the geometrical superfield formalism to derive the local,
covariant and continuous Becchi-Rouet-Stora-Tyutin (BRST) symmetry
transformations and the non-local, non-covariant and continuous dual-BRST
symmetry transformations for the free Abelian one-form gauge theory in four -dimensions (4D) of spacetime. Our discussion is carried out in the
framework of BRST invariant Lagrangian density for the above 4D theory in the
Feynman gauge. The geometrical origin and interpretation for the (dual-)BRST
charges (and the transformations they generate) are provided in the language of
translations of some superfields along the Grassmannian directions of the six
(-dimensional supermanifold parametrized by the four spacetime and two
Grassmannian variables.Comment: LaTeX file, 23 page
About one long-range contribution to K+ -> pi+ l+ l- decays
We investigate the mechanism of K+ -> pi+ l+ l- (l= e, mu) decays in which a
virtual photon is emitted either from the incoming K+ or the outgoing pi+. We
point out some inconsistencies with and between two previous calculations,
discuss the possible experimental inputs, and estimate the branching fractions.
This mechanism alone fails to explain the existing experimental data by more
than one order-of-magnitude. But it may show itself by its interference with
the leading long-range mechanism dominated by the a_1^+ and rho^0 mesons.Comment: 12 pages, RevTeX, epsf.sty, 2 embedded figure
Cohomological aspects of Abelian gauge theory
We discuss some aspects of cohomological properties of a two-dimensional free
Abelian gauge theory in the framework of BRST formalism. We derive the
conserved and nilpotent BRST- and co-BRST charges and express the Hodge
decomposition theorem in terms of these charges and a conserved bosonic charge
corresponding to the Laplacian operator. It is because of the topological
nature of free U(1) gauge theory that the Laplacian operator goes to zero when
equations of motion are exploited. We derive two sets of topological invariants
which are related to each-other by a certain kind of duality transformation and
express the Lagrangian density of this theory as the sum of terms that are
BRST- and co-BRST invariants. Mathematically, this theory captures together
some of the key features of Witten- and Schwarz type of topological field
theories.Comment: 12 pages, LaTeX, no figures, Title and text have been slightly
changed, Journal reference is given and a reference has been adde
A non-linear Oscillator with quasi-Harmonic behaviour: two- and -dimensional Oscillators
A nonlinear two-dimensional system is studied by making use of both the
Lagrangian and the Hamiltonian formalisms. The present model is obtained as a
two-dimensional version of a one-dimensional oscillator previously studied at
the classical and also at the quantum level. First, it is proved that it is a
super-integrable system, and then the nonlinear equations are solved and the
solutions are explicitly obtained. All the bounded motions are quasiperiodic
oscillations and the unbounded (scattering) motions are represented by
hyperbolic functions. In the second part the system is generalized to the case
of degrees of freedom. Finally, the relation of this nonlinear system with
the harmonic oscillator on spaces of constant curvature, two-dimensional sphere
and hyperbolic plane , is discussed.Comment: 30 pages, 4 figures, submitted to Nonlinearit
Path Integral Quantization of Generalized Quantum Electrodynamics
In this paper, a complete covariant quantization of generalized
electrodynamics is shown through the path integral approach. To this goal, we
first studied the hamiltonian structure of system following Dirac's methodology
and, then, we followed the Faddeev-Senjanovic procedure to obtain the
transition amplitude. The complete propagators (Schwinger-Dyson-Fradkin
equations) of the correct gauge fixation and the generalized
Ward-Fradkin-Takahashi identities are also obtained. Afterwards, an explicit
calculation of one-loop approximation of all Green's functions and a discussion
about the obtained results are presented.Comment: 25 pages, 5 figure
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