87 research outputs found
Damped Bloch oscillations of cold atoms in optical lattices
The paper studies Bloch oscillations of cold neutral atoms in the optical
lattice. The effect of spontaneous emission on the dynamics of the system is
analyzed both analytically and numerically. The spontaneous emission is shown
to cause (i) the decay of Bloch oscillations with the decrement given by the
rate of spontaneous emission and (ii) the diffusive spreading of the atoms with
a diffusion coefficient depending on {\em both} the rate of spontaneous
emission and the Bloch frequency.Comment: 10 pages, 8 figure
The first dozen years of the history of ITEP Theoretical Physics Laboratory
The theoretical investigations at ITEP in the years 1945-1958 are reviewed.
There are exposed the most important theoretical results, obtained in the
following branches of physics: 1) the theory of nuclear reactors on thermal
neutrons; 2) the hydrogen bomb project ("Tube" in USSR and "Classical Super" in
USA); 3) radiation theory; ~4) low temperature physics; 5) quantum
electrodynamics and quantum field theories; 6) parity violation in weak
interactions, the theory of -decay and other weak processes; 7) strong
interaction and nuclear physics. To the review are added the English
translations of few papers, originally published in Russian, but unknown (or
almost unknown) to Western readers.Comment: 55 pages, 5 fig
Fluctuation induced hopping and spin polaron transport
We study the motion of free magnetic polarons in a paramagnetic background of
fluctuating local moments. The polaron can tunnel only to nearby regions of
local moments when these fluctuate into alignment. We propose this fluctuation
induced hopping as a new transport mechanism for the spin polaron. We calculate
the diffusion constant for fluctuation induced hopping from the rate at which
local moments fluctuate into alignment. The electrical resistivity is then
obtained via the Einstein relation. We suggest that the proposed transport
mechanism is relevant in the high temperature phase of the Mn pyrochlore
colossal magneto resistance compounds and Europium hexaboride.Comment: 8 pages, 3 figure
Simulating (electro)hydrodynamic effects in colloidal dispersions: smoothed profile method
Previously, we have proposed a direct simulation scheme for colloidal
dispersions in a Newtonian solvent [Phys.Rev.E 71,036707 (2005)]. An improved
formulation called the ``Smoothed Profile (SP) method'' is presented here in
which simultaneous time-marching is used for the host fluid and colloids. The
SP method is a direct numerical simulation of particulate flows and provides a
coupling scheme between the continuum fluid dynamics and rigid-body dynamics
through utilization of a smoothed profile for the colloidal particles.
Moreover, the improved formulation includes an extension to incorporate
multi-component fluids, allowing systems such as charged colloids in
electrolyte solutions to be studied. The dynamics of the colloidal dispersions
are solved with the same computational cost as required for solving
non-particulate flows. Numerical results which assess the hydrodynamic
interactions of colloidal dispersions are presented to validate the SP method.
The SP method is not restricted to particular constitutive models of the host
fluids and can hence be applied to colloidal dispersions in complex fluids
Universality and scaling study of the critical behavior of the two-dimensional Blume-Capel model in short-time dynamics
In this paper we study the short-time behavior of the Blume-Capel model at
the tricritical point as well as along the second order critical line. Dynamic
and static exponents are estimated by exploring scaling relations for the
magnetization and its moments at early stage of the dynamic evolution. Our
estimates for the dynamic exponents, at the tricritical point, are and .Comment: 12 pages, 9 figure
Granular Solid Hydrodynamics
Granular elasticity, an elasticity theory useful for calculating static
stress distribution in granular media, is generalized to the dynamic case by
including the plastic contribution of the strain. A complete hydrodynamic
theory is derived based on the hypothesis that granular medium turns
transiently elastic when deformed. This theory includes both the true and the
granular temperatures, and employs a free energy expression that encapsulates a
full jamming phase diagram, in the space spanned by pressure, shear stress,
density and granular temperature. For the special case of stationary granular
temperatures, the derived hydrodynamic theory reduces to {\em hypoplasticity},
a state-of-the-art engineering model.Comment: 42 pages 3 fi
Time-Space Noncommutativity in Gravitational Quantum Well scenario
A novel approach to the analysis of the gravitational well problem from a
second quantised description has been discussed. The second quantised formalism
enables us to study the effect of time space noncommutativity in the
gravitational well scenario which is hitherto unavailable in the literature.
The corresponding first quantized theory reveals a leading order perturbation
term of noncommutative origin. Latest experimental findings are used to
estimate an upper bound on the time--space noncommutative parameter. Our
results are found to be consistent with the order of magnitude estimations of
other NC parameters reported earlier.Comment: 7 pages, revTe
A Weyl-Dirac Cosmological Model with DM and DE
In the Weyl-Dirac (W-D) framework a spatially closed cosmological model is
considered. It is assumed that the space-time of the universe has a chaotic
Weylian microstructure but is described on a large scale by Riemannian
geometry. Locally fields of the Weyl connection vector act as creators of
massive bosons having spin 1. It is suggested that these bosons, called
weylons, provide most of the dark matter in the universe. At the beginning the
universe is a spherically symmetric geometric entity without matter. Primary
matter is created by Dirac's gauge function very close to the beginning. In the
early epoch, when the temperature of the universe achieves its maximum,
chaotically oriented Weyl vector fields being localized in micro-cells create
weylons. In the dust dominated period Dirac's gauge function is giving rise to
dark energy, the latter causing the cosmic acceleration at present. This
oscillatory universe has an initial radius identical to the Plank length =
1.616 exp (-33) cm, at present the cosmic scale factor is 3.21 exp (28) cm,
while its maximum value is 8.54 exp (28) cm. All forms of matter are created by
geometrically based functions of the W-D theory.Comment: 25 pages. Submitted to GR
Two-body decays in the minimal 331 model
The two-body decays of the extra neutral boson Z_2 predicted by the minimal
331 model are analyzed. At the three-level it can decay into standard model
particles as well as exotic quarks and the new gauge bosons predicted by the
model. The decays into a lepton pair are strongly suppressed, with and . In the bosonic
sector, Z_2 would decay mainly into a pair of bilepton gauge bosons, with a
branching ratio below the 0.1 level. The Z_2 boson has thus a leptophobic and
bileptophobic nature and it would decay dominantly into quark pairs. The
anomaly-induced decays and , which occurs
at the one-loop level are studied. It is found that and at most. As for the and decays, with H a relatively light Higgs boson, they
are induced via Z'-Z mixing. It is obtained that
and . We also examine the flavor changing neutral
current decays and , which may have branching
fractions as large as and , respectively, and thus may be of
phenomenological interest.Comment: 14 pages, 3 figures, submitted to Physical Review
Dynamical stability of infinite homogeneous self-gravitating systems: application of the Nyquist method
We complete classical investigations concerning the dynamical stability of an
infinite homogeneous gaseous medium described by the Euler-Poisson system or an
infinite homogeneous stellar system described by the Vlasov-Poisson system
(Jeans problem). To determine the stability of an infinite homogeneous stellar
system with respect to a perturbation of wavenumber k, we apply the Nyquist
method. We first consider the case of single-humped distributions and show
that, for infinite homogeneous systems, the onset of instability is the same in
a stellar system and in the corresponding barotropic gas, contrary to the case
of inhomogeneous systems. We show that this result is true for any symmetric
single-humped velocity distribution, not only for the Maxwellian. If we
specialize on isothermal and polytropic distributions, analytical expressions
for the growth rate, damping rate and pulsation period of the perturbation can
be given. Then, we consider the Vlasov stability of symmetric and asymmetric
double-humped distributions (two-stream stellar systems) and determine the
stability diagrams depending on the degree of asymmetry. We compare these
results with the Euler stability of two self-gravitating gaseous streams.
Finally, we determine the corresponding stability diagrams in the case of
plasmas and compare the results with self-gravitating systems
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