20,407 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
Non-Anticommutative Deformations of N=(1,1) Supersymmetric Theories
We discuss chirality-preserving nilpotent deformations of four-dimensional
N=(1,1) Euclidean harmonic superspace and their implications in N=(1,1)
supersymmetric gauge and hypermultiplet theories, basically following
[hep-th/0308012] and [hep-th/0405049]. For the SO(4) x SU(2) invariant
deformation, we present non-anticommutative Euclidean analogs of the N=2 gauge
multiplet and hypermultiplet off-shell actions. As a new result, we consider a
specific non-anticommutative hypermultiplet model with N=(1,0) supersymmetry.
It involves free scalar fields and interacting right-handed spinor fields.Comment: Latex file, 15 pages, Submitted to Proceedings of the Seminar
``Classical and Quantum Integrable Systems'' (Dubna, Russia, January 26-29,
2004), v.2 with minor correction
Self-Dual N=2 Born-Infeld Theory Through Auxiliary Superfields
There is an evidence that the N=2 Born-Infeld theory with spontaneously
broken N=4 supersymmetry exhibits self-duality. We perform a further check of
this hypothesis by constructing a new representation for the N=2 Born-Infeld
action through the auxiliary chiral superfield U. In such a formulation,
self-duality is equivalent to U(1) invariance of the U interaction. We
explicitly calculate the auxiliary interaction up to the 10th order and show
its U(1) duality invariance, thus proving that the original action is self-dual
to the same order. We also suggest a new method of recursive computation of the
N=2 Born-Infeld action in the standard formulation, based solely on the
nonlinear realization of the N=4 central charge on the N=2 superfield strengths
W, \bar W.Comment: 1 + 31 pages, substantial revision: an important Note and Appendix C
added; section 2 corrected and expanded; some typos, eq. (5.13) and Appendix
B correcte
Quantum diffusion of dipole-oriented indirect excitons in coupled quantum wells
A model for diffusion of statistically-degenerate excitons in (coupled)
quantum wells is proposed and analysed. Within a microscopic approach, we
derive a quantum diffusion equation, calculate and estimate the self-diffusion
coefficient for excitons in quantum wells and derive a modified Einstein
relation adapted to statistically-degenerated quasi-two-dimensional bosons. It
is also shown that the dipole-dipole interaction of indirect excitons
effectively screens long-range-correlated disorder in quantum wells. Numerical
calculations are given for indirect excitons in GaAs/AlGaAs coupled quantum
wells.Comment: To appear in Europhysics Letter
SU(2) reductions in N=4 multidimensional supersymmetric mechanics
We perform an su(2) Hamiltonian reduction in the bosonic sector of the
su(2)-invariant action for two free (4, 4, 0) supermultiplets. As a result, we
get the five dimensional N=4 supersymmetric mechanics describing the motion of
an isospin carrying particle interacting with a Yang monopole. We provide the
Lagrangian and Hamiltonian descriptions of this system. Some possible
generalizations of the action to the cases of systems with a more general
bosonic action, a four-dimensional system which still includes eight fermionic
components, and a variant of five-dimensional N=4 mechanics constructed with
the help of the ordinary and twisted N=4 hypermultiplets were also considered.Comment: 11 pages, LaTeX file, no figures; 3 references added, minor
correction
Dielectric response of Anderson and pseudogapped insulators
Using a combination of analytic and numerical methods, we study the
polarizability of a (non-interacting) Anderson insulator in one, two, and three
dimensions and demonstrate that, in a wide range of parameters, it scales
proportionally to the square of the localization length, contrary to earlier
claims based on the effective-medium approximation. We further analyze the
effect of electron-electron interactions on the dielectric constant in
quasi-1D, quasi-2D and 3D materials with large localization length, including
both Coulomb repulsion and phonon-mediated attraction. The phonon-mediated
attraction (in the pseudogapped state on the insulating side of the
Superconductor-Insulator Transition) produces a correction to the dielectric
constant, which may be detected from a linear response of a dielectric constant
to an external magnetic field.Comment: 9 page
High harmonic generation in crystals using Maximally Localized Wannier functions
In this work, the nonlinear optical response, and in particular, the high
harmonic generation of semiconductors is addressed by using the Wannier gauge.
One of the main problems in the time evolution of the Semiconductor Bloch
equations resides in the fact that the dipole couplings between different bands
can diverge and have a random phase along the reciprocal space and this leads
to numerical instability. To address this problem, we propose the use of the
Maximally Localized Wannier functions that provide a framework to map ab-initio
calculations to an effective tight-binding Hamiltonian with great accuracy. We
show that working in the Wannier gauge, the basis set in which the Bloch
functions are constructed directly from the Wannier functions, the dipole
couplings become smooth along the reciprocal space thus avoiding the problem of
random phases. High harmonic generation spectrum is computed for a 2D monolayer
of hBN as a numerical demonstration
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