19,695 research outputs found
Monte Carlo simulation of Ising model on directed Barabasi-Albert network
The existence of spontaneous magnetization of Ising spins on directed
Barabasi-Albert networks is investigated with seven neighbors, by using Monte
Carlo simulations. In large systems we see the magnetization for different
temperatures T to decay after a characteristic time tau, which is extrapolated
to diverge at zero temperature.Comment: Error corrected, main conclusion unchanged; for Int. J. Mod. Phys. C
16, issue 4 (2005
Critical velocity of a mobile impurity in one-dimensional quantum liquids
We study the notion of superfluid critical velocity in one spatial dimension.
It is shown that for heavy impurities with mass exceeding a critical mass
, the dispersion develops periodic metastable branches resulting
in dramatic changes of dynamics in the presence of an external driving force.
In contrast to smooth Bloch Oscillations for , a heavy impurity
climbs metastable branches until it reaches a branch termination point or
undergoes a random tunneling event, both leading to an abrupt change in
velocity and an energy loss. This is predicted to lead to a non-analytic
dependence of the impurity drift velocity on small forces.Comment: 5 pages, 2 figures; New version with Supplemental Material (3 pages,
6 figures); Accepted to PR
Vector order parameter in general relativity. Covariant equations
Phase transitions with spontaneous symmetry breaking and vector order
parameter are considered in multidimensional theory of general relativity.
Covariant equations, describing the gravitational properties of topological
defects, are derived. The topological defects are classified in accordance with
the symmetry of the covariant derivative of the vector order parameter. The
abilities of the derived equations are demonstrated in application to the brane
world concept. New solutions of the Einstein equations with a transverse vector
order parameter are presented. In the vicinity of phase transition the
solutions are found analytically
Low energy excitations and singular contributions in the thermodynamics of clean Fermi liquids
Using a recently suggested method of bosonization in an arbitrary dimension,
we study the anomalous contribution of the low energy spin and charge
excitations to thermodynamic quantities of a two-dimensional (2D) Fermi liquid.
The method is slightly modified for the present purpose such that the effective
supersymmetric action no longer contains the high energy degrees of freedom but
still accounts for effects of the finite curvature of the Fermi surface.
Calculating the anomalous contribution to the specific heat, we
show that the leading logarithmic in temperature corrections to can be obtained in a scheme combining a summation of ladder diagrams
and renormalization group equations. The final result is represented as the sum
of two separate terms that can be interpreted as coming from singlet and
triplet superconducting excitations. The latter may diverge in certain regions
of the coupling constants, which should correspond to the formation of triplet
Cooper pairs.Comment: 29 pages, 13 figure
Probing the ZZgamma and Zgammagamma Couplings Through the Process e+e- --> nu anti-nu gamma
We study the sensitivity for testing the anomalous triple gauge couplings
and via the process
at high energy linear colliders. For integrated luminosities of 500
and center of mass energies between 0.5 and 1.5 , we find that this
process can provide tests of the triple neutral gauge boson couplings of order
, one order of magnitude lower than the standard model prediction.Comment: 12 pages, 6 figure
Temperature dependence of the spin susceptibility of a clean Fermi gas with repulsion
Spin susceptibility of a clean Fermi gas with repulsion in any dimension is
considered using a supersymmetric low energy theory of interacting spin
excitations and renormalization scheme recently proposed by Aleiner and Efetov
[cond-mat/0602309]. We generalize this method to include the coupling to the
magnetic field. As a result, we obtain for the correction to the
Pauli susceptibility a non-analytic temperature dependence of the form in dimensions where is an
effective -dependent logarithmically renormalized backscattering amplitude.
In one dimension, is proportional to , and we
reproduce a well known result obtained long ago by a direct calculation.Comment: 25 pages, 10 figure
Vanishing bulk viscosities and conformal invariance of unitary Fermi gas
By requiring general-coordinate and conformal invariance of the hydrodynamic
equations, we show that the unitary Fermi gas has zero bulk viscosity, zeta=0,
in the normal phase. In the superfluid phase, two of the bulks viscosities have
to vanish, zeta_1=zeta_2=0, while the third one zeta_3 is allowed to be
nonzero.Comment: 4 page
Non-Universality in Semi-Directed Barabasi-Albert Networks
In usual scale-free networks of Barabasi-Albert type, a newly added node
selects randomly m neighbors from the already existing network nodes,
proportionally to the number of links these had before. Then the number N(k) of
nodes with k links each decays as 1/k^gamma where gamma=3 is universal, i.e.
independent of m. Now we use a limited directedness in the construction of the
network, as a result of which the exponent gamma decreases from 3 to 2 for
increasing m.Comment: 5 pages including 2 figures and computer progra
Klein-Gordon and Dirac particles in non-constant scalar-curvature background
The Klein-Gordon and Dirac equations are considered in a semi-infinite lab
() in the presence of background metrics and with . These metrics have non-constant scalar-curvatures. Various aspects of the
solutions are studied. For the first metric with , it is shown
that the spectrums are discrete, with the ground state energy for spin-0 particles. For , the spectrums are
found to be continuous. For the second metric with , each
particle, depends on its transverse-momentum, can have continuous or discrete
spectrum. For Klein-Gordon particles, this threshold transverse-momentum is
, while for Dirac particles it is . There is no solution for
case. Some geometrical properties of these metrics are also
discussed.Comment: 14 pages, LaTeX, to be published in Int. Jour. Mod. Phys.
Slow light in moving media
We review the theory of light propagation in moving media with extremely low
group velocity. We intend to clarify the most elementary features of
monochromatic slow light in a moving medium and, whenever possible, to give an
instructive simplified picture
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