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$_c$ superconductors. The emergence of higher harmonics, besides the simple sinusoid $I_{c}\sin\phi$, 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$_2$ planes in cuprates, are considered. The critical temperature suppression, observed at values of hole doping close to $p=1/8$, 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 $45^\circ$ grain boundaries can produce long-range strain fields that results in the width of the magnetic sheet along the boundary of the order of $0.5 \div 1 \mu m$ at temperatures grater than the bulk Curie temperature by about $10^2$ 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 $s$ and $Q^2$. 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 $c\bar c$ pair on its trajectory through nuclear matter, (ii) dependence on the finite lifetime of the $c\bar c$ 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 $s$ 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