37 research outputs found
Paraxial propagation in amorphous optical media with screw dislocation
We study paraxial beam propagation parallel to the screw axis of a dislocated
amorphous medium that is optically weakly inhomogeneous and isotropic. The
effect of the screw dislocation on the beam's orbital angular momentum is shown
to change the optical vortex strength, rendering vortex annihilation or
generation possible. Furthermore, the dislocation is shown to induce a weak
\textit{biaxial} anisotropy in the medium due to the elasto-optic effect, which
changes the beam's spin angular momentum as well as causing precession of the
polarization. We derive the equations of motion of the beam and demonstrate the
optical Hall effect in the dislocated medium. Its application with regard to
determining the Burgers vector as well as the elasto-optic coefficients of the
medium is explained
Superselection from canonical constraints
The evolution of both quantum and classical ensembles may be described via
the probability density P on configuration space, its canonical conjugate S,
and an_ensemble_ Hamiltonian H[P,S]. For quantum ensembles this evolution is,
of course, equivalent to the Schroedinger equation for the wavefunction, which
is linear. However, quite simple constraints on the canonical fields P and S
correspond to_nonlinear_ constraints on the wavefunction. Such constraints act
to prevent certain superpositions of wavefunctions from being realised, leading
to superselection-type rules. Examples leading to superselection for energy,
spin-direction and `classicality' are given. The canonical formulation of the
equations of motion, in terms of a probability density and its conjugate,
provides a universal language for describing classical and quantum ensembles on
both continuous and discrete configuration spaces, and is briefly reviewed in
an appendix.Comment: MiKTex 2.3, no figures, minor clarifications, to appear in J. Phys.
One-loop approximation of Moller scattering in Krein-space quantization
It has been shown that the negative-norm states necessarily appear in a
covariant quantization of the free minimally coupled scalar field in de Sitter
spacetime [1,2]. In this processes ultraviolet and infrared divergences have
been automatically eliminated [3]. A natural renormalization of the one-loop
interacting quantum field in Minkowski spacetime () has been
achieved through the consideration of the negative-norm states defined in Krein
space. It has been shown that the combination of quantum field theory in Krein
space together with consideration of quantum metric fluctuation, results in
quantum field theory without any divergences [4]. Pursuing this approach, we
express Wick's theorem and calculate M{\o}ller scattering in the one-loop
approximation in Krein space. The mathematical consequence of this method is
the disappearance of the ultraviolet divergence in the one-loop approximation.Comment: 10 page
Berry effect in acoustical polarization transport in phononic crystals
We derive the semiclassical equations of motion of a transverse acoustical
wave packet propagating in a phononic crystal subject to slowly varying
perturbations. The formalism gives rise to Berry effect terms in the equations
of motion, manifested as the Rytov polarization rotation law and the
polarization-dependent Hall effect. We show that the formalism is also
applicable to the case of non-periodic inhomogeneous media, yielding explicit
expressions for the Berry effect terms.Comment: To appear in JETP Let
Dependence of interface conductivity on relevant physical parameters in polarized Fermi mixtures
We consider a mass-asymmetric polarized Fermi system in the presence of
Hartree-Fock (HF) potentials. We concentrate on the BCS regime with various
interaction strengths and numerically obtain the allowed values of the chemical
and HF potentials, as well as the mass ratio. The functional dependence of the
heat conductivity of the N-SF interface on relevant physical parameters, namely
the temperature, the mass ratio, and the interaction strength, is obtained. In
particular, we show that the interface conductivity starts to drop with
decreasing temperature at the temperature, , where the mean
kinetic energy of the particles is just sufficient to overcome the SF gap. We
obtain as a function of the mass ratio and the interaction
strength. The variation of the heat conductivity, at fixed temperature, with
the HF potentials and the imbalance chemical potential is also obtained.
Finally, because the range of relevant temperatures increases for larger values
of the mass ratio, we consider the - mixture
separately by taking the temperature dependence of the pair potential into
account.Comment: To appear in Physica C (2012
Linear response of heat conductivity of normal-superfluid interface of a polarized Fermi gas to orbital magnetic field
Using perturbed Bogoliubov equations, we study the linear response to a weak
orbital magnetic field of the heat conductivity of the normal-superfluid
interface of a polarized Fermi gas at sufficiently low temperature. We consider
the various scattering regions of the BCS regime and analytically obtain the
transmission coefficients and the heat conductivity across the interface in an
arbitrary weak orbital field. For a definite choice of the field, we consider
various values of the scattering length in the BCS range and numerically obtain
the allowed values of the average and species-imbalance chemical potentials.
Thus, taking Andreev reflection into account, we describe how the heat
conductivity is affected by the field and the species imbalance. In particular,
we show that the additional heat conductivity due to the orbital field
increases with the species imbalance, which is more noticeable at higher
temperatures. Our results indicate how the heat conductivity may be controlled,
which is relevant to sensitive magnetic field sensors/regulators at the
interface.Comment: To appear in Physica B (2011
Macroscopic effects of the spectral structure in turbulent flows
Two aspects of turbulent flows have been the subject of extensive, split
research efforts: macroscopic properties, such as the frictional drag
experienced by a flow past a wall, and the turbulent spectrum. The turbulent
spectrum may be said to represent the fabric of a turbulent state; in practice
it is a power law of exponent \alpha (the "spectral exponent") that gives the
revolving velocity of a turbulent fluctuation (or "eddy") of size s as a
function of s. The link, if any, between macroscopic properties and the
turbulent spectrum remains missing. Might it be found by contrasting the
frictional drag in flows with differing types of spectra? Here we perform
unprecedented measurements of the frictional drag in soap-film flows, where the
spectral exponent \alpha = 3 and compare the results with the frictional drag
in pipe flows, where the spectral exponent \alpha = 5/3. For moderate values of
the Reynolds number Re (a measure of the strength of the turbulence), we find
that in soap-film flows the frictional drag scales as Re^{-1/2}, whereas in
pipe flows the frictional drag scales as Re^{-1/4} . Each of these scalings may
be predicted from the attendant value of \alpha by using a new theory, in which
the frictional drag is explicitly linked to the turbulent spectrum. Our work
indicates that in turbulence, as in continuous phase transitions, macroscopic
properties are governed by the spectral structure of the fluctuations.Comment: 6 pages, 3 figure