3,191 research outputs found
Power corrections and perturbative coupling from lattice gauge thoeries
From the analysis of the perturbative expansion of the lattice regularized
gluon condensate, toghether with MC data, we present evidence of OPE-unexpected
dim-2 power corrections in the scaling behaviour of the Wilson loop. These can
be interpreted as an indication that in lattice gauge theories the running
coupling at large momentum contains contributions of order Q^2.Comment: 3 pages, 2 figures. Talk given at the Lattice97 conference,
Edinburgh, U
Once more on extra quark-lepton generations and precision measurements
Precision measurements of -boson parameters and -boson and -quark
masses put strong constraints on non singlet New Physics. We
demonstrate that one extra generation passes electroweak constraints even when
all new particle masses are well above their direct mass bounds.Comment: Dedicated to L.B. Okun's 80th birthda
Magnetized Tolman-Bondi Collapse
We investigate the gravitational implosion of magnetized matter by studying
the inhomogeneous collapse of a weakly magnetized Tolman-Bondi spacetime. The
role of the field is analyzed by looking at the convergence of neighboring
particle worldlines. In particular, we identify the magnetically related
stresses in the Raychaudhuri equation and use the Tolman-Bondi metric to
evaluate their impact on the collapsing dust. We find that, despite the low
energy level of the field, the Lorentz force dominates the advanced stages of
the collapse, leading to a strongly anisotropic contraction. In addition, of
all the magnetic stresses, those that resist the collapse are found to grow
faster.Comment: 6 pages, RevTex; v2: physical interpretation of the results slightly
changed, references added, version accepted in Phys. Rev. D (2006
Poisson Brackets Scheme for Vortex Dynamics in Superfluids and Superconductors and Effect of Band Structure of Crystal
Poisson brackets for the Hamiltonian dynamics of vortices are discussed for 3
regimes, in which the dissipation can be neglected and the vortex dynamics is
reversible: (i) The superclean regime when the spectral flow is suppressed.
(ii) The regime when the fermions are pinned by crystal lattice. This includes
also the regime of the extreme spectral flow of fermions in the vortex core:
these fermions are effectively pinned by the normal component. (iii) The case
when the vortices are strongly pinned by the normal component. All these limits
are described by the single parameter , which physical meaning is
discussed for superconductors containing several bands of electrons and holes.
The effect of the Fermi-surface topology on the vortex dynamics is also
discussed.Comment: LaTeX file, 11 pages, no figures, version accepted in JETP Letter
Dirac fermions in strong electric field and quantum transport in graphene
Our previous results on the nonperturbative calculations of the mean current
and of the energy-momentum tensor in QED with the T-constant electric field are
generalized to arbitrary dimensions. The renormalized mean values are found;
the vacuum polarization and particle creation contributions to these mean
values are isolated in the large T-limit, the vacuum polarization contributions
being related to the one-loop effective Euler-Heisenberg Lagrangian.
Peculiarities in odd dimensions are considered in detail. We adapt general
results obtained in 2+1 dimensions to the conditions which are realized in the
Dirac model for graphene. We study the quantum electronic and energy transport
in the graphene at low carrier density and low temperatures when quantum
interference effects are important. Our description of the quantum transport in
the graphene is based on the so-called generalized Furry picture in QED where
the strong external field is taken into account nonperturbatively; this
approach is not restricted to a semiclassical approximation for carriers and
does not use any statistical assumtions inherent in the Boltzmann transport
theory. In addition, we consider the evolution of the mean electromagnetic
field in the graphene, taking into account the backreaction of the matter field
to the applied external field. We find solutions of the corresponding
Dirac-Maxwell set of equations and with their help we calculate the effective
mean electromagnetic field and effective mean values of the current and the
energy-momentum tensor. The nonlinear and linear I-V characteristics
experimentally observed in both low and high mobility graphene samples is quite
well explained in the framework of the proposed approach, their peculiarities
being essentially due to the carrier creation from the vacuum by the applied
electric field.Comment: 24 pages, 1 figure; version accepted for publication in Physical
Review D., some comments adde
Theory for the single-point velocity statistics of fully developed turbulence
We investigate the single-point velocity probability density function (PDF)
in three-dimensional fully developed homogeneous isotropic turbulence within
the framework of PDF equations focussing on deviations from Gaussianity. A
joint analytical and numerical analysis shows that these deviations may be
quantified studying correlations of dynamical quantities like pressure
gradient, external forcing and energy dissipation with the velocity. A
stationary solution for the PDF equation in terms of these quantities is
presented, and the theory is validated with the help of direct numerical
simulations indicating sub-Gaussian tails of the PDF.Comment: 6 pages, 4 figures, corrected typo in eq. (4
London's limit for the lattice superconductor
A stability problem for the current state of the strong coupling
superconductor has been considered within the lattice Ginzburg-Landau model.
The critical current problem for a thin superconductor film is solved within
the London limit taking into account the crystal lattice symmetry. The current
dependence on the order parameter modulus is computed for the superconductor
film for various coupling parameter magnitudes. The field penetration problem
is shown to be described in this case by the one-dimensional sine-Gordon
equation. The field distribution around the vortex is described at the same
time by the two-dimensional elliptic sine-Gordon equation.Comment: 7 pages, 3 figures, Revtex4, mostly technical correction; extended
abstrac
Kinetic equation for a dense soliton gas
We propose a general method to derive kinetic equations for dense soliton
gases in physical systems described by integrable nonlinear wave equations. The
kinetic equation describes evolution of the spectral distribution function of
solitons due to soliton-soliton collisions. Owing to complete integrability of
the soliton equations, only pairwise soliton interactions contribute to the
solution and the evolution reduces to a transport of the eigenvalues of the
associated spectral problem with the corresponding soliton velocities modified
by the collisions. The proposed general procedure of the derivation of the
kinetic equation is illustrated by the examples of the Korteweg -- de Vries
(KdV) and nonlinear Schr\"odinger (NLS) equations. As a simple physical example
we construct an explicit solution for the case of interaction of two cold NLS
soliton gases.Comment: 4 pages, 1 figure, final version published in Phys. Rev. Let
Critical density of a soliton gas
We quantify the notion of a dense soliton gas by establishing an upper bound
for the integrated density of states of the quantum-mechanical Schr\"odinger
operator associated with the KdV soliton gas dynamics. As a by-product of our
derivation we find the speed of sound in the soliton gas with Gaussian spectral
distribution function.Comment: 7 page
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