11,517 research outputs found
Super Landau Models on Odd Cosets
We construct d=1 sigma models of the Wess-Zumino type on the SU(n|1)/U(n)
fermionic cosets. Such models can be regarded as a particular supersymmetric
extension (with a target space supersymmetry) of the classical Landau model,
when a charged particle possesses only fermionic coordinates. We consider both
classical and quantum models, and prove the unitarity of the quantum model by
introducing the metric operator on the Hilbert space of the quantum states,
such that all their norms become positive-definite. It is remarkable that the
quantum n=2 model exhibits hidden SU(2|2) symmetry. We also discuss the planar
limit of these models. The Hilbert space in the planar n=2 case is shown to
carry SU(2|2) symmetry which is different from that of the SU(2|1)/U(1) model.Comment: 1 + 33 pages, some typos correcte
Array of Josephson junctions with a non-sinusoidal current-phase relation as a model of the resistive transition of unconventional superconductors
An array of resistively and capacitively shunted Josephson junctions with
nonsinusoidal current-phase relation is considered for modelling the transition
in high-T superconductors. The emergence of higher harmonics, besides the
simple sinusoid , is expected for dominant \emph{d}-wave
symmetry of the Cooper pairs, random distribution of potential drops, dirty
grains, or nonstationary conditions. We show that additional cosine and sine
terms act respectively by modulating the global resistance and by changing the
Josephson coupling of the mixed superconductive-normal states. First, the
approach is applied to simulate the transition in disordered granular
superconductors with the weak-links characterized by nonsinusoidal
current-phase relation. In granular superconductors, the emergence of
higher-order harmonics affects the slope of the transition. Then, arrays of
intrinsic Josephson junctions, naturally formed by the CuO planes in
cuprates, are considered. The critical temperature suppression, observed at
values of hole doping close to , is investigated. Such suppression,
related to the sign change and modulation of the Josephson coupling across the
array, is quantified in terms of the intensities of the first and second
sinusoids of the current-phase relation. Applications are envisaged for the
design and control of quantum devices based on stacks of intrinsic Josephson
junctions.Comment: Added: comparison with experiments; reference
Enhancement of magnetic ordering by the stress fields of grain boundaries in ferromagnets
In the paper we predict a distinctive change of magnetic properties and
considerable increase of the Curie temperature caused by the strain fields of
grain boundaries in ferromagnetic films. It is shown that a sheet of
spontaneous magnetization may arise along a grain boundary at temperatures
greater than the bulk Curie temperature. The temperature dependence and space
distribution of magnetization in a ferromagnetic film with grain boundaries are
calculated. We found that grain boundaries can produce long-range
strain fields that results in the width of the magnetic sheet along the
boundary of the order of at temperatures grater than the
bulk Curie temperature by about K.Comment: 5 pages, 3 Figures include
Electroproduction of Charmonia off Protons and Nuclei
Elastic virtual photoproduction of charmonia on nucleons is calculated in a
parameter free way with the light-cone dipole formalism and the same input:
factorization in impact parameters, light-cone wave functions for the photons
and the charmonia, and the universal phenomenological dipole cross section
which is fitted to other data. The charmonium wave functions are calculated
with four known realistic potentials, and two models for the dipole cross
section are tested. Very good agreement with data for the cross section of
charmonium electroproduction is found in a wide range of and . Using
the ingredients from those calculations we calculate also exclusive
electroproduction of charmonia off nuclei. Here new effects become important,
(i) color filtering of the pair on its trajectory through nuclear
matter, (ii) dependence on the finite lifetime of the fluctuation
(coherence length) and (iii) gluon shadowing in a nucleus compared to the one
in a nucleon. Total coherent and incoherent cross sections for C, Cu and Pb as
functions of are presented. The results can be tested with future
electron-nucleus colliders or in the peripheral collisions of relativistic
heavy ions.Comment: Talk at 2-nd International Workshop on Hadron Physics, 25-29
September 2002, Coimbra, Portugal. To appear in the Workshop Proceedings
(will be published by the American Institute of Physics
Quark model description of the tetraquark state X(3872) in a relativistic constituent quark model with infrared confinement
We explore the consequences of treating the X(3872) meson as a tetraquark
bound state. As dynamical framework we employ a relativistic constituent quark
model which includes infrared confinement in an effective way. We calculate the
decay widths of the observed channels X-> Jpsi+2\pi (3\pi) and X-> \bar
D0+D0+\pi0 via the intermediate off--shell states X-> Jpsi+\rho(\omega) and X->
\bar D + D*. For reasonable values of the size parameter of the X(3872) we find
consistency with the available experimental data. We also discuss the possible
impact of the X(3872) in a s-channel dominance description of the
Jpsi-dissociation cross section.Comment: 9 pages, 5 figures; discussion and references added, accepted in
Phys. Rev.
Nonlinear Realization of Spontaneously Broken N=1 Supersymmetry Revisited
This paper revisits the nonlinear realization of spontaneously broken N=1
supersymmetry. It is shown that the constrained superfield formalism can be
reinterpreted in the language of standard realization of nonlinear
supersymmetry via a new and simpler route. Explicit formulas of actions are
presented for general renormalizable theories with or without gauge
interactions. The nonlinear Wess-Zumino gauge is discussed and relations are
pointed out for different definitions of gauge fields. In addition, a general
procedure is provided to deal with theories of arbitrary Kahler potentials.Comment: 1+18 pages, LaTe
The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/d-wave superconductor contact
The influence of phase shifts of electron waves passing through and reflected
by the potential barrier on the Andreev reflection in a
ferromagnet/isolator/d-wave superconductor (FIS) contact is studied. It is
found that in a superconductor the surface spin-dependent Andreev bound states
inside the superconducting gap are formed as a result of the interference of
electron-like and hole-like quasiparticles due to repeated Andreev reflections.
The peak in the conductance of the FIS contact at the zero potential for the
(110)-oriented superconductor disappears rapidly as the polarization of a
ferromagnet increases, whereas for the (100)-oriented superconductor it
appears. The physical reason for this behavior of conductance is discussed.Comment: 8 pages, 4 figure
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