1,530 research outputs found
Destruction of a metastable string by particle collisions
We calculate the probability of destruction of a metastable string by
collisions of the Goldstone bosons, corresponding to the transverse waves on
the string. We find a general formula that allows to determine the probability
of the string breakup by a collision of arbitrary number of the bosons. We find
that the destruction of a metastable string takes place only in collisions of
even number of the bosons, and we explicitly calculate the energy dependence of
such process in a two-particle collision for an arbitrary relation between the
energy and the largest infrared scale in the problem, the length of the
critical gap in the string.Comment: 15 pages, 1 figur
Fractal dimension crossovers in turbulent passive scalar signals
The fractal dimension of turbulent passive scalar signals is
calculated from the fluid dynamical equation. depends on the
scale. For small Prandtl (or Schmidt) number one gets two ranges,
for small scale r and =5/3 for large r, both
as expected. But for large one gets a third, intermediate range in
which the signal is extremely wrinkled and has . In that
range the passive scalar structure function has a plateau. We
calculate the -dependence of the crossovers. Comparison with a numerical
reduced wave vector set calculation gives good agreement with our predictions.Comment: 7 pages, Revtex, 3 figures (postscript file on request
Particle and particle pair dispersion in turbulence modeled with spatially and temporally correlated stochastic processes
In this paper we present a new model for modeling the diffusion and relative
dispersion of particles in homogeneous isotropic turbulence. We use an
Heisenberg-like Hamiltonian to incorporate spatial correlations between fluid
particles, which are modeled by stochastic processes correlated in time. We are
able to reproduce the ballistic regime in the mean squared displacement of
single particles and the transition to a normal diffusion regime for long
times. For the dispersion of particle pairs we find a -dependence of the
mean squared separation at short times and a -dependence for long ones. For
intermediate times indications for a Richardson law are observed in
certain situations. Finally the influence of inertia of real particles on the
dispersion is investigated.Comment: 10 pages, 7 figures, 1 tabl
Semiclassical Calculation of Photon-Stimulated Schwinger Pair Creation
We consider the electron-positron pair creation by a photon in an external
constant electric field. The presented treatment is based on a purely
quasiclassical calculation of the imaginary part of the on-shell photon
polarization operator. By using this approach we find the pair production rate
for photons with polarization parallel as well as orthogonal to the external
electric field in the leading order in the parameter , which has
been recently found by other methods. For the orthogonal polarization we also
find a new contribution to the rate, which is leading in the ratio of the
photon energy to the electron mass . We also reproduce by a purely
geometrical calculation the exponential factor in the probability of the
stimulated pair creation at arbitrary energy of the photon.Comment: 16 pages, 4 figure
- …