3,579 research outputs found
A homomorphism theorem and a Trotter product formula for quantum stochastic flows with unbounded coefficients
We give a new method for proving the homomorphic property of a quantum
stochastic ow satisfying a quantum stochastic differential equation with
unbounded coefficients, under some further hypotheses. As an application, we
prove a Trotter product formula for quantum stochastic ows and obtain quantum
stochastic dilations of a class of quantum dynamical semigroups generalizing
results of [5
Topological Defects on Fluctuating Surfaces: General Properties and the Kosterlitz-Thouless Transition
We investigate the Kosterlitz-Thouless transition for hexatic order on a free
fluctuating membrane and derive both a Coulomb gas and a sine-Gordon
Hamiltonian to describe it. The Coulomb-gas Hamiltonian includes charge
densities arising from disclinations and from Gaussian curvature. There is an
interaction coupling the difference between these two densities, whose strength
is determined by the hexatic rigidity, and an interaction coupling Gaussian
curvature densities arising from the Liouville Hamiltonian resulting from the
imposition of a covariant cutoff. In the sine-Gordon Hamiltonian, there is a
linear coupling between a scalar field and the Gaussian curvature. We discuss
gauge-invariant correlation function for hexatic order and the dielectric
constant of the Coulomb gas. We also derive renormalization group recursion
relations that predict a transition with decreasing bending rigidity .Comment: REVTEX, 45 pages with 11 postscript figures compressed using uufiles.
Accepted for publication in Phys. Rev.
On the Spontaneous CP Breaking in the Higgs Sector of the Minimal Supersymmetric Standard Model
We revise a recently proposed mechanism for spontaneous CP breaking at finite
temperature in the Higgs sector of the Minimal Supersymmetric Standard Model,
based on the contribution of squarks, charginos and neutralinos to the one-loop
effective potential. We have included plasma effects for all bosons and added
the contribution of neutral scalar and charged Higgses. While the former have
little effect, the latter provides very strong extra constraints on the
parameter space and change drastically the previous results. We find that CP
can be spontaneously broken at the critical temperature of the electroweak
phase transition without any fine-tuning in the parameter space.Comment: 9 pages, LATEX, 3 appended postscript figures, IEM-FT-76/9
Semiclassical force for electroweak baryogenesis: three-dimensional derivation
We derive a semiclassical transport equation for fermions propagating in the
presence of a CP-violating planar bubble wall at a first order electroweak
phase transition. Starting from the Kadanoff-Baym (KB) equation for the
two-point (Wightman) function we perform an expansion in gradients, or
equivalently in the Planck constant h-bar. We show that to first order in h-bar
the KB equations have a spectral solution, which allows for an on-shell
description of the plasma excitations. The CP-violating force acting on these
excitations is found to be enhanced by a boost factor in comparison with the
1+1-dimensional case studied in a former paper. We find that an identical
semiclassical force can be obtained by the WKB method. Applications to the MSSM
are also mentioned.Comment: 19 page
External cadmium and internal calcium block of single calcium channels in smooth muscle cells from rabbit mesenteric artery
The patch clamp technique was used to record unitary currents through single calcium channels from smooth muscle cells of rabbit mesenteric arteries. The effects of external cadmium and cobalt and internal calcium, barium, cadmium, and magnesium on single channel currents were investigated with 80 mM barium as the charge carrier and Bay K 8644 to prolong openings. External cadmium shortened the mean open time of single Ca channels. Cadmium blocking and unblocking rate constants of 16.5 mM-1 ms-1 and 0.6 ms-1, respectively, were determined, corresponding to dissociation constant Kd of 36 microM at -20 mV. These results are very similar to those reported for cardiac muscle Ca channels (Lansman, J. B., P. Hess, and R. W. Tsien. 1986. J. Gen. Physiol. 88:321–347). In contrast, Cd2+ (01–10 mM), when applied to the internal surface of Ca channels in inside-out patches, did not affect the mean open time, mean unitary current, or the variance of the open channel current. Internal calcium induced a flickery block, with a Kd of 5.8 mM. Mean blocking and unblocking rate constants for calcium of 0.56 mM-1 ms-1 and 3.22 ms-1, respectively, were determined. Internal barium (8 mM) reduced the mean unitary current by 36%. We conclude that under our experimental conditions, the Ca channel is not symmetrical with respect to inorganic ion block and that intracellular calcium can modulate Ca channel currents via a low-affinity binding site
Mixing-induced CP violating sources for electroweak baryogenesis from a semiclassical approach
The effects of flavor mixing in electroweak baryogenesis is investigated in a
generalized semiclassical WKB approach. Through calculating the nonadiabatic
corrections to the particle currents it is shown that extra CP violation
sources arise from the off-diagonal part of the equation of motion of particles
moving inside the bubble wall. This type of mixing-induced source is of the
first order in derivative expansion of the Higgs condensate, but is oscillation
suppressed. The numerical importance of the mixing-induced source is discussed
in the Minimal Supersymmetric Standard Model and compared with the source term
induced by semiclassical force. It is found that in a large parameter space
where oscillation suppression is not strong enough, the mixing-induced source
can dominate over that from the semiclassical force.Comment: 19 pp, 2 figs, 1 table, some comments added, to appear in
Eur.Phys.J.
Aspect-ratio dependence of the spin stiffness of a two-dimensional XY model
We calculate the superfluid stiffness of 2D lattice hard-core bosons at
half-filling (equivalent to the S=1/2 XY-model) using the squared winding
number quantum Monte Carlo estimator. For L_x x L_y lattices with aspect ratio
L_x/L_y=R, and L_x,L_y -> infinity, we confirm the recent prediction [N.
Prokof'ev and B.V. Svistunov, Phys. Rev. B 61, 11282 (1999)] that the
finite-temperature stiffness parameters \rho^W_x and \rho^W_y determined from
the winding number differ from each other and from the true superfluid density
\rho_s. Formally, \rho^W_y -> \rho_s in the limit in which L_x -> infinity
first and then L_y -> infinity. In practice we find that \rho^W_y converges
exponentially to \rho_s for R>1. We also confirm that for 3D systems, \rho^W_x
= \rho^W_y = \rho^W_z = \rho_s for any R. In addition, we determine the
Kosterlitz-Thouless transition temperature to be T_KT/J=0.34303(8) for the 2D
model.Comment: 7 pages, 8 figures, 1 table. Minor changes to published versio
Montecarlo simulation of the role of defects as the melting mechanism
We study in this paper the melting transition of a crystal of fcc structure
with the Lennard-Jones potential, by using isobaric-isothermal Monte Carlo
simulations.
Local and collective updates are sequentially used to optimize the
convergence. We show the important role played by defects in the melting
mechanism in favor of modern melting theories.Comment: 6 page, 10 figures included. Corrected version to appear in Phys.
Rev.
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Explosive morphology from fractal analysis of micrographs
The effect of particle size on the details of the initiation and detonation of condensed explosives has long been known. The effect of the three-dimensional nature of explosive particles as a neat pressings (with voids), or as dispersed in a second (or third) phase (with or without voids), has been the subject of many investigations of detonation phenomena. However, succinct and accurate descriptions of the compacts and pressings are difficult to achieve because the morphology and size distributions are generally altered by processing into useful configurations and densities. Three-dimensional measurements of near-full-density pressings are not easy and have not been done with great accuracy. The authors explore the analysis of various particle-size and morphological measurements using the formalisms of fractal geometry. They intend to show, by a combination of modeling and data analysis, that a three-dimensional description of the explosive, the binder, and the voids can be constructed from one- and two-dimensional measurements of surface. In the long term, they hope to correlate these descriptions with the measurements of explosive behavior
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