3,684 research outputs found
The classical sphaleron transition rate exists and is equal to
Results of a large scale numerical simulation show that the high temperature
Chern-Simons number diffusion rate in the electroweak theory has a classical
limit , where and
is the weak fine structure constant.Comment: 12 pages, plain LaTeX, figures part of the LaTeX source, minor errors
corrected, acknowledgment added, to be published in Phys. Lett.
Spectral theory for the failure of linear control in a nonlinear stochastic system
We consider the failure of localized control in a nonlinear spatially
extended system caused by extremely small amounts of noise. It is shown that
this failure occurs as a result of a nonlinear instability. Nonlinear
instabilities can occur in systems described by linearly stable but strongly
nonnormal evolution operators. In spatially extended systems the nonnormality
manifests itself in two different but complementary ways: transient
amplification and spectral focusing of disturbances. We show that temporal and
spatial aspects of the nonnormality and the type of nonlinearity are all
crucially important to understanding and describing the mechanism of nonlinear
instability. Presented results are expected to apply equally to other physical
systems where strong nonnormality is due to the presence of mean flow rather
than the action of control.Comment: Submitted to Physical Review
Chern-Simons term in the 4-dimensional SU(2) Higgs Model
Using Seiberg's definition for the geometric charge in SU(2) lattice gauge
theory, we have managed to apply it also to the Chern-Simons term. We checked
the periodic structure and determined the Chern-Simons density on small
lattices and with L=4,\, 6,\mbox{ and }8 near the
critical region in the SU(2) Higgs model. The data indicate that tunneling is
increased at high temperature.Comment: 7 pages plus 4 PS figure
Comment on "Magnetic quantum oscillations of the conductivity in layered conductors"
We discuss the recent theory of Gvozdikov [Phys. Rev. B 70, 085113 (2004)]
which aims at explaining the Shubnikov-de Haas oscillations of the longitudinal
resistivity \rho_zz observed in the quasi-two-dimensional organic compound
\beta''-(BEDT-TTF)_2SF_5CH_2CF_2SO_3.
We point out that the self-consistent equations of the theory yielding the
longitudinal resistivity and the magnetic field dependence of the chemical
potential have been incorrectly solved. We show that the consideration of the
self-consistent Born approximation (which determines the relaxation rate in
Gvozdikov's paper) leads in fact to the complete absence of the longitudinal
conductivity \sigma_{zz} at leading order in high magnetic fields.Comment: 4 pages, no figur
A portable MBE system for in situ X-Ray investigations at synchrotron beamlines
A portable synchrotron MBE system is designed and applied for in situ
investigations. The growth chamber is equipped with all the standard MBE
components such as effusion cells with shutters, main shutter, cooling shroud,
manipulator, RHEED setup and pressure gauges. The characteristic feature of the
system is the beryllium windows which are used for in situ x-ray measurements.
An UHV sample transfer case allows in-vacuo transfer of samples prepared
elsewhere. We describe the system design and demonstrate it's performance by
investigating the annealing process of buried InGaAs self organized quantum
dots
Reply to "Comment on 'Origin of combination frequencies in quantum magnetic oscillations of two-dimensional multiband metals' " by A.S. Alexandrov and A.M. Bratkovsky [cond-mat/0207173]
In their comment on the paper (Phys. Rev. B 65, 153403 (2002);
cond-mat/0110154), Alexandrov and Bratkovsky (cond-mat/0207173) argue that they
correctly took into account the chemical potential oscillations in their
analytical theory of combination frequencies in multiband low-dimensional
metals by expanding the free energy in powers of the chemical potential
oscillations. In this reply, we show that this claim contradicts their original
paper (Phys. Rev. B 63, 033105 (2001)). We demonstrate that the condition given
for the expansion is mathematically incorrect. The correct condition allows to
understand the limits of validity of the analytical theory.Comment: 4 page
Theory of the Shubnikov-de Haas effect in quasi-two-dimensional metals
The Shubnikov - de Haas effect in quasi-two-dimensional normal metals is
studied. The interlayer conductivity is calculated using the Kubo formula. The
electron scattering on short-range is considered in the self-consistent Born
approximation. The result obtained differs from that derived from the Boltzmann
transport equation. This difference is shown to be a general feature of
conductivity in magnetic field. A detailed description of the two new
qualitative effects -- the field-dependent phase shift of beats and of the slow
oscillations of conductivity is provided. The results obtained are applicable
to strongly anisotropic organic metals and to other quasi-two-dimensional
compounds.Comment: 10 page
On reduced models for superstrings on AdS_n x S^n
We review the Pohlmeyer reduction procedure of the superstring sigma model on
AdS_n x S^n leading to a gauged WZW model with an integrable potential coupled
to 2d fermions. In particular, we consider the case of the Green-Schwarz
superstring on AdS_3 x S^3 supported by RR flux. The bosonic part of the
reduced model is given by the sum of the complex sine-Gordon Lagrangian and its
sinh-Gordon counterpart. We determine the corresponding fermionic part and
discuss possible existence of hidden 2d supersymmetry in the reduced action. We
also elaborate on some general aspects of the Pohlmeyer reduction applied to
the AdS_5 x S^5 superstring.Comment: 24 page
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