53 research outputs found
Two electrons in an external oscillator potential: hidden algebraic structure
It is shown that the Coulomb correlation problem for a system of two
electrons (two charged particles) in an external oscillator potential possesses
a hidden -algebraic structure being one of recently-discovered
quasi-exactly-solvable problems. The origin of existing exact solutions to this
problem, recently discovered by several authors, is explained. A degeneracy of
energies in electron-electron and electron-positron correlation problems is
found. It manifests the first appearence of hidden -algebraic structure
in atomic physics.Comment: 7 pages (plus one figure avaliable via direct request), LaTeX,
Preprint IFUNAM FT 94-4
Physical realization of the parity anomaly and quantum hall effect
We present the lattice version of the anomalous Dirac operator in (2+1) dimensions. This version is associated with a group of magnetic translations rather than translations. This group naturally provided homologically nontrivial fiber bundles, the first Chern class of which is directly related with the number of zero modes and spectral asymmetry of the Dirac operator. The results are in agreement with the lattice fermions doubling phenomenon. The relation of the parity anomaly in (2+1) and the Hall effect is elucidated
Raman scattering and anomalous current algebra in Mott insulators
We present a theory of large shift Raman scattering in Mott insulators and show that inelastic light scattering provides information about electronic current algebra. We argue that the recent experiment where a new excitation below the optical absorption threshold was observed in crossed polarizations gives evidence of anomalous terms in the current alegebra. We show that it suggests there exists an exciton bound state with a topological magnetic excitation with odd parity with respect to a spatial reflection
Hierarchical Structure of Azbel-Hofstader Problem: Strings and loose ends of Bethe Ansatz
We present numerical evidence that solutions of the Bethe Ansatz equations
for a Bloch particle in an incommensurate magnetic field (Azbel-Hofstadter or
AH model), consist of complexes-"strings". String solutions are well-known from
integrable field theories. They become asymptotically exact in the
thermodynamic limit. The string solutions for the AH model are exact in the
incommensurate limit, where the flux through the unit cell is an irrational
number in units of the elementary flux quantum.
We introduce the notion of the integral spectral flow and conjecture a
hierarchical tree for the problem. The hierarchical tree describes the topology
of the singular continuous spectrum of the problem. We show that the string
content of a state is determined uniquely by the rate of the spectral flow
(Hall conductance) along the tree. We identify the Hall conductances with the
set of Takahashi-Suzuki numbers (the set of dimensions of the irreducible
representations of with definite parity).
In this paper we consider the approximation of noninteracting strings. It
provides the gap distribution function, the mean scaling dimension for the
bandwidths and gives a very good approximation for some wave functions which
even captures their multifractal properties. However, it misses the
multifractal character of the spectrum.Comment: revtex, 30 pages, 6 Figs, 8 postscript files are enclosed, important
references are adde
Theta-terms in nonlinear sigma-models
We trace the origin of theta-terms in non-linear sigma-models as a
nonperturbative anomaly of current algebras. The non-linear sigma-models emerge
as a low energy limit of fermionic sigma-models. The latter describe Dirac
fermions coupled to chiral bosonic fields. We discuss the geometric phases in
three hierarchies of fermionic sigma-models in spacetime dimension (d+1) with
chiral bosonic fields taking values on d-, d+1-, and d+2-dimensional spheres.
The geometric phases in the first two hierarchies are theta-terms. We emphasize
a relation between theta-terms and quantum numbers of solitons.Comment: 10 pages, no figures, revtex, typos correcte
Quantum Group and Magnetic Translations. Bethe-Ansatz Solution for Azbel-Hofstadter Problem
We present a new approach to the problem of Bloch electrons in magnetic (
sometimes called Azbel-Hofstadter problem) field, by making explicit a natural
relation between the group of magnetic translations and the quantum group
. The approach allows us to express the "mid" band spectrum of the
model and the Bloch wave function as solutions of the Bethe-Ansatz equations
typical for completely integrable quantum systems. The zero mode wave functions
are found explicitly in terms of -deformed classical orthogonal
polynomials.In this paper we present solution for the isotropic problem. We
also present a class of solvable quasiperiodic equations related to
.Comment: 19 pages, Revte
Energy Reflection Symmetry of Lie-Algebraic Problems: Where the Quasiclassical and Weak Coupling Expansions Meet
We construct a class of one-dimensional Lie-algebraic problems based on sl(2)
where the spectrum in the algebraic sector has a dynamical symmetry E -> - E.
All 2j+1 eigenfunctions in the algebraic sector are paired, and inside each
pair are related to each other by simple analytic continuation x -> ix, except
the zero mode appearing if j is integer. At j-> infinity the energy of the
highest level in the algebraic sector can be calculated by virtue of the
quasiclassical expansion, while the energy of the ground state can be
calculated as a weak coupling expansion. The both series coincide identically.Comment: Latex, 16 pages, 3 figures. Minor styllistic changes made, typos
corrected, a remark on the energy-reflection symmetry in the
quantum-algebraic Hamiltonians emerging in finite-difference problems added.
Final version, to be published in Physical Review
Topological Mechanism of Superconductivity
We outline the basic ideas of the topological mechanisms of
superconductivity. A gauged model of correlated electronic system where a
topological fluid is formed as a result of a strong interaction is discussed.Comment: 38 pages, latex, no figure
Ground state energy and quasiparticle gaps in FQHE states
Applying the transformation of fermion operators to new fermion
quasiparticles introduced by Halperin, Lee, and Read we estimate a scaling
behavior of the ground state energy and quasiparticle gaps as a function of
filling fraction for a "principal sequence" of FQHE
states converging towards the gapless state at half filling. The exponent
describing the shape of the cusp is
found to be greater than one and to depend nontrivially on the interaction
potential. The dependence of quasiparticle gaps agrees with the results of
recent measurements by R.R.Du et al.Comment: 15 pages, TeX, C Version 3.0, preprint ETH-TH/93-3
Anderson-Yuval approach to the multichannel Kondo problem
We analyze the structure of the perturbation expansion of the general
multichannel Kondo model with channel anisotropic exchange couplings and in the
presence of an external magnetic field, generalizing to this case the
Anderson-Yuval technique. For two channels, we are able to map the Kondo model
onto a generalized resonant level model. Limiting cases in which the equivalent
resonant level model is solvable are identified. The solution correctly
captures the properties of the two channel Kondo model, and also allows an
analytic description of the cross-over from the non Fermi liquid to the Fermi
liquid behavior caused by the channel anisotropy.Comment: 23 pages, ReVTeX, 4 figures av. on reques
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