3,584 research outputs found
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
Monopole decay in the external electric field
The possibility of the magnetic monopole decay in the constant electric field
is investigated and the exponential factor in the probability is obtained.
Corrections due to Coulomb interaction are calculated. The relation between
masses of particles for the process to exist is obtained.Comment: 13 pages, 8 figure
Particle decay in false vacuum
We revisit the problem of decay of a metastable vacuum induced by the
presence of a particle. For the bosons of the `master field' the problem is
solved in any number of dimensions in terms of the spontaneous decay rate of
the false vacuum, while for a fermion we find a closed expression for the decay
rate in (1+1) dimensions. It is shown that in the (1+1) dimensional case an
infrared problem of one-loop correction to the decay rate of a boson is
resolved due to a cancellation between soft modes of the field. We also find
the boson decay rate in the `sine-Gordon staircase' model in the limits of
strong and weak coupling.Comment: 19 pages, 2 figure
The XYZs of Charmonium at BES
This contribution reviews some recent developments in charmonium
spectroscopy, and discusses related theoretical predictions. The spectrum of
states, strong decays of states above open charm threshold, electromagnetic
transitions, and issues related to the recent discoveries of the "XYZ" states
are discussed. Contributions that BES can make to our understanding of
charmonium and related states are stressed in particular.Comment: 5 pages, 1 eps figure. Invited contribution to the International
Workshop on Tau-Charm Physics Charm2006 (5-7 June 2006, Beijing, China
Degenerate Domain Wall Solutions in Supersymmetric Theories
A family of degenerate domain wall configurations, partially preserving
supersymmetry, is discussed in a generalized Wess-Zumino model with two scalar
superfields. We establish some general features inherent to the models with
continuously degenerate domain walls. For instance, for purely real
trajectories additional "integrals of motion" exist. The solution for the
profile of the scalar fields for any wall belonging to the family is found in
quadratures for arbitrary ratio of the coupling constants. For a special value
of this ratio the solution family is obtained explicitly in terms of elementary
functions. We also discuss the threshold amplitudes for multiparticle
production generated by these solutions. New unexpected nullifications of the
threshold amplitudes are found.Comment: 21 pages, LaTeX, 3 figures using epsf.st
Elliptic flow contribution to two-particle correlations at different orientations to the reaction plane
Collective anisotropic particle flow, a general phenomenon present in
relativistic heavy-ion collisions, can be separated from direct
particle-particle correlations of different physics origin by virtue of its
specific azimuthal pattern. We provide expressions for flow-induced
two-particle azimuthal correlations, if one of the particles is detected under
fixed directions with respect to the reaction plane. We consider an ideal case
when the reaction plane angle is exactly known, as well as present the general
expressions in case of finite event-plane resolution. We foresee applications
for the study of generic two-particle correlations at large transverse momentum
originating from jet fragmentation.Comment: 5 pages, 3 figures, to be published as Rapid Communications in
Phys.Rev.C Re-submit paper to with small improvements in text for better
understanding, some minor changes in notation, and correcting one formula
where a summation was forgotten. One new reference, one reference to
conference report removed since full paper was already reference
Top quark longitudinal polarization near the threshold in l+ l- annihilation
We show that the longitudinal polarization of the top quarks produced in the
annihilation of e+ e- or mu+ mu- into tbar t at energies near the threshold is
not affected by the large Coulomb-type corrections, which greatly modify the
total cross section. Thus the longitudinal polarization, although small, may
provide an independent information on the mass and the width of the top quark,
largely independent of the uncertainty in alpha_s.Comment: 6 pages, LaTeX, no figures, added references, corrected typo
Stochastic current switching in bistable resonant tunneling systems
Current-voltage characteristics of resonant-tunneling structures often
exhibit intrinsic bistabilities. In the bistable region of the I-V curve one of
the two current states is metastable. The system switches from the metastable
state to the stable one at a random moment in time. The mean switching time
\tau depends exponentially on the bias measured from the boundary of the
bistable region V_{th}. We find full expressions for \tau (including
prefactors) as functions of bias, sample geometry, and in-plane conductivity.
Our results take universal form upon appropriate renormalization of the
threshold voltage V_{th}. We also show that in large samples the switching
initiates inside, at the edge, or at a corner of the sample depending on the
parameters of the system.Comment: 21 pages, 5 figure
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