58,633 research outputs found
Suppression of compressible edge channels and spatial spin polarization in the integer quantum Hall regime
We perform systematic numerical studies of the structure of spin-resolved
compressible strips in split-gate quantum wires taking into account the
exchange and correlation interactions within the density functional theory in
the local spin-density approximation. We find that for realistic parameters of
the wire the exchange interaction can completely suppress the formation of the
compressible strips. As the depletion length or magnetic field are increased,
the compressible strips starts to form first for the spin-down and then for
spin-up edge channels. We demonstrate that the widths of these strips plus the
spatial separation between them caused by the exchange interaction are equal to
the width of the compressible strip calculated in the Hartree approximation for
spinless electrons. We also discuss the effect of electron density on the
suppression of the compressible strips in quantum wires.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Quantum walks with an anisotropic coin I: spectral theory
We perform the spectral analysis of the evolution operator U of quantum walks
with an anisotropic coin, which include one-defect models, two-phase quantum
walks, and topological phase quantum walks as special cases. In particular, we
determine the essential spectrum of U, we show the existence of locally
U-smooth operators, we prove the discreteness of the eigenvalues of U outside
the thresholds, and we prove the absence of singular continuous spectrum for U.
Our analysis is based on new commutator methods for unitary operators in a
two-Hilbert spaces setting, which are of independent interest.Comment: 26 page
Massless and massive one-loop three-point functions in negative dimensional approach
In this article we present the complete massless and massive one-loop
triangle diagram results using the negative dimensional integration method
(NDIM). We consider the following cases: massless internal fields; one massive,
two massive with the same mass m and three equal masses for the virtual
particles. Our results are given in terms of hypergeometric and
hypergeometric-type functions of external momenta (and masses for the massive
cases) where the propagators in the Feynman integrals are raised to arbitrary
exponents and the dimension of the space-time D. Our approach reproduces the
known results as well as other solutions as yet unknown in the literature.
These new solutions occur naturally in the context of NDIM revealing a
promising technique to solve Feynman integrals in quantum field theories
Implications of a new light gauge boson for neutrino physics
We study the impact of light gauge bosons on neutrino physics. We show that
they can explain the NuTeV anomaly and also escape the constraints from
neutrino experiments if they are very weakly coupled and have a mass of a few
GeV. Lighter gauge bosons with stronger couplings could explain both the NuTeV
anomaly and the positive anomalous magnetic moment of the muon. However, in the
simple model we consider in this paper (say a purely vectorial extra U(1)
current), they appear to be in conflict with the precise measurements of \nu-e
elastic scattering cross sections. The surprising agreement that we obtain
between our naive model and the NuTeV anomaly for a Z' mass of a few GeV may be
a coincidence. However, we think it is interesting enough to deserve attention
and perhaps a more careful analysis, especially since a new light gauge boson
is a very important ingredient for the Light Dark Matter scenario.Comment: 9 page
The dilute A_L models and the integrable perturbations of unitary minimal CFTs
Recently, a set of thermodynamic Bethe ansatz equations is proposed by Dorey,
Pocklington and Tateo for unitary minimal models perturbed by \phi_{1,2} or
\phi_{2,1} operator. We examine their results in view of the lattice analogues,
dilute A_L models at regime 1 and 2. Taking M_{5,6}+\phi_{1,2} and
M_{3,4}+\phi_{2,1} as the simplest examples, we will explicitly show that the
conjectured TBA equations can be recovered from the lattice model in a scaling
limit.Comment: 14 pages, 2 figure
Vacuum type of SU(2) gluodynamics in maximally Abelian and Landau gauges
The vacuum type of SU(2) gluodynamics is studied using Monte-Carlo
simulations in maximally Abelian (MA) gauge and in Landau (LA) gauge, where the
dual Meissner effect is observed to work. The dual Meissner effect is
characterized by the coherence and the penetration lengths. Correlations
between Wilson loops and electric fields are evaluated in order to measure the
penetration length in both gauges. The coherence length is shown to be fixed in
the MA gauge from measurements of the monopole density around the static
quark-antiquark pair. It is also shown numerically that a dimension 2 gluon
operator A^+A^-(s) and the monopole density has a strong correlation as
suggested theoretically. Such a correlation is observed also between the
monopole density and A^2(s)= A^+A^-(s) + A^3A^3(s) condensate if the remaining
U(1) gauge degree of freedom is fixed to U(1) Landau gauge (U1LA). The
coherence length is determined numerically also from correlations between
Wilson loops and A^+A^-(s) and A^2(s) in MA + U1LA gauge. Assuming that the
same physics works in the LA gauge, we determine the coherence length from
correlations between Wilson loops and A^2(s). Penetration lengths and coherence
lengths in the two gauges are almost the same. The vacuum type of the
confinement phase in both gauges is near to the border between the type 1 and
the type 2 dual superconductors.Comment: 13 pages, 22 figures, RevTeX 4 styl
Fourth Order Algorithms for Solving the Multivariable Langevin Equation and the Kramers Equation
We develop a fourth order simulation algorithm for solving the stochastic
Langevin equation. The method consists of identifying solvable operators in the
Fokker-Planck equation, factorizing the evolution operator for small time steps
to fourth order and implementing the factorization process numerically. A key
contribution of this work is to show how certain double commutators in the
factorization process can be simulated in practice. The method is general,
applicable to the multivariable case, and systematic, with known procedures for
doing fourth order factorizations. The fourth order convergence of the
resulting algorithm allowed very large time steps to be used. In simulating the
Brownian dynamics of 121 Yukawa particles in two dimensions, the converged
result of a first order algorithm can be obtained by using time steps 50 times
as large. To further demostrate the versatility of our method, we derive two
new classes of fourth order algorithms for solving the simpler Kramers equation
without requiring the derivative of the force. The convergence of many fourth
order algorithms for solving this equation are compared.Comment: 19 pages, 2 figure
One-loop N-point equivalence among negative-dimensional, Mellin-Barnes and Feynman parametrization approaches to Feynman integrals
We show that at one-loop order, negative-dimensional, Mellin-Barnes' (MB) and
Feynman parametrization (FP) approaches to Feynman loop integrals calculations
are equivalent. Starting with a generating functional, for two and then for
-point scalar integrals we show how to reobtain MB results, using
negative-dimensional and FP techniques. The point result is valid for
different masses, arbitrary exponents of propagators and dimension.Comment: 11 pages, LaTeX. To be published in J.Phys.
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