903 research outputs found
Time-Loop Formalism for Irreversible Quantum Problems: Steady State Transport in Junctions with Asymmetric Dynamics
Non-unitary quantum mechanics has been used in the past to study
irreversibility, dissipation and decay in a variety of physical systems. In
this letter, we propose a general scheme to deal with systems governed by
non-Hermitian Hamiltonians. We argue that the Schwinger-Keldysh formalism gives
a natural description for those problems. To elucidate the method, we study a
simple model inspired by mesoscopic physics --an asymmetric junction. The
system is governed by a non-Hermitian Hamiltonian which captures essential
aspects of irreversibility.Comment: 4 pages, 4 figure
Deep inelastic scattering and final state interaction in an exactly solvable relativistic model
In the theory of deep inelastic scattering (DIS) the final state interaction
(FSI) between the struck quark and the remnants of the target is usually
assumed to be negligible in the Bjorken limit. This assumption, still awaiting
a full validation within nonperturbative QCD, is investigated in a model
composed by two relativistic particles, interacting via a relativistic harmonic
oscillator potential, within light-cone hamiltonian dynamics. An
electromagnetic current operator whose matrix elements behave properly under
Poincar\'e transformations is adopted. It is shown that: i) the parton model is
recovered, once the standard parton model assumptions are adopted; and ii) when
relativistic, interacting eigenfunctions are exactly taken into account for
both the initial and final states, the values of the structure functions,
averaged over small, but finite intervals of the Bjorken variable , coincide
with the results of the parton model in the Bjorken limit.Comment: 26 pages, to appear in Phys. Rev. C (May 1998
Tunneling currents in ferromagnetic systems with multiple broken symmetries
SHORTENED ABSTRACT: A system exhibiting multiple simultaneously broken
symmetries offers the opportunity to influence physical phenomena such as
tunneling currents by means of external control parameters. In this paper, we
consider the broken SU(2) (internal spin) symmetry of ferromagnetic systems
coexisting with \textit{i)} the broken U(1) symmetry of superconductors and
\textit{ii)} the broken spatial inversion symmetry induced by a Rashba term in
a spin-orbit coupling Hamiltonian. In order to study the effect of these broken
symmetries, we consider tunneling currents that arise in two different systems;
tunneling junctions consisting of non-unitary spin-triplet ferromagnetic
superconductors and junctions consisting of ferromagnets with spin-orbit
coupling.Comment: Accepted for publication in Phys. Rev.
Random Matrix Theory and higher genus integrability: the quantum chiral Potts model
We perform a Random Matrix Theory (RMT) analysis of the quantum four-state
chiral Potts chain for different sizes of the chain up to size L=8. Our
analysis gives clear evidence of a Gaussian Orthogonal Ensemble statistics,
suggesting the existence of a generalized time-reversal invariance.
Furthermore a change from the (generic) GOE distribution to a Poisson
distribution occurs when the integrability conditions are met. The chiral Potts
model is known to correspond to a (star-triangle) integrability associated with
curves of genus higher than zero or one. Therefore, the RMT analysis can also
be seen as a detector of ``higher genus integrability''.Comment: 23 pages and 10 figure
Perspectives: Quantum Mechanics on Phase Space
The basic ideas in the theory of quantum mechanics on phase space are
illustrated through an introduction of generalities, which seem to underlie
most if not all such formulations and follow with examples taken primarily from
kinematical particle model descriptions exhibiting either Galileian or
Lorentzian symmetry. The structures of fundamental importance are the relevant
(Lie) groups of symmetries and their homogeneous (and associated) spaces that,
in the situations of interest, also possess Hamiltonian structures. Comments
are made on the relation between the theory outlined and a recent paper by
Carmeli, Cassinelli, Toigo, and Vacchini.Comment: "Quantum Structures 2004" - Meeting of the International Quantum
Structures Association; Denver, Colorado; 17-22 July, 200
Relativistic Partial Wave Analysis Using the Velocity Basis of the Poincare Group
The velocity basis of the Poincare group is used in the direct product space
of two irreducible unitary representations of the Poincare group. The velocity
basis with total angular momentum j will be used for the definition of
relativistic Gamow vectors.Comment: 14 pages; revte
Realism and the wave-function
Realism -- the idea that the concepts in physical theories refer to 'things'
existing in the real world -- is introduced as a tool to analyze the status of
the wave-function. Although the physical entities are recognized by the
existence of invariant quantities, examples from classical and quantum physics
suggest that not all the theoretical terms refer to the entities: some terms
refer to properties of the entities, and some terms have only an epistemic
function. In particular, it is argued that the wave-function may be written in
terms of classical non-referring and epistemic terms. The implications for
realist interpretations of quantum mechanics and on the teaching of quantum
physics are examined.Comment: No figure
Wigner Crystal in One Dimension
A one--dimensional gas of electrons interacting with long--range Coulomb
forces () is investigated. The excitation spectrum consists
of separate collective charge and spin modes, with the charge excitation
energies in agreement with RPA calculations. For arbitrarily weak Coulomb
repulsion density correlations at wavevector decay extremely slowly and
are best described as those of a one--dimensional Wigner crystal. Pinning of
the Wigner crystal then leads to the nonlinear transport properties
characteristic of CDW. The results allow a consistent interpretation of the
plasmon and spin excitations observed in one--dimensional semiconductor
structures, and suggest an interpretation of some of the observed features in
terms of ``spinons''. A possible explanation for nonlinear transport phenomena
is given.Comment: 10 pages, RevTe
The Question of Low-Lying Intruder States in and Neighboring Nuclei
The presence of not yet detected intruder states in e.g. a
intruder at 9 excitation would affect the shape of the -delayed alpha spectra of and . In order to test the
plausibility of this assumption, shell model calculations with up to excitations in (and up to excitations in
) were performed. With the above restrictions on the model spaces, the
calculations did not yield any low-lying intruder state in . Another
approach -the simple deformed oscillator model with self-consistent frequencies
and volume conservation gives an intruder state in which is lower in
energy than the above shell model results, but its energy is still considerably
higher than 9 .Comment: 16 pages (RevTeX), 1 PS figure. To appear in Phys. Rev.
Semiclassical approach to discrete symmetries in quantum chaos
We use semiclassical methods to evaluate the spectral two-point correlation
function of quantum chaotic systems with discrete geometrical symmetries. The
energy spectra of these systems can be divided into subspectra that are
associated to irreducible representations of the corresponding symmetry group.
We show that for (spinless) time reversal invariant systems the statistics
inside these subspectra depend on the type of irreducible representation. For
real representations the spectral statistics agree with those of the Gaussian
Orthogonal Ensemble (GOE) of Random Matrix Theory (RMT), whereas complex
representations correspond to the Gaussian Unitary Ensemble (GUE). For systems
without time reversal invariance all subspectra show GUE statistics. There are
no correlations between non-degenerate subspectra. Our techniques generalize
recent developments in the semiclassical approach to quantum chaos allowing one
to obtain full agreement with the two-point correlation function predicted by
RMT, including oscillatory contributions.Comment: 26 pages, 8 Figure
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