286 research outputs found
Sensitivity to perturbations and quantum phase transitions
The local density of states or its Fourier transform, usually called fidelity
amplitude, are important measures of quantum irreversibility due to imperfect
evolution. In this Rapid Communication we study both quantities in a
paradigmatic many body system, the Dicke Hamiltonian, where a single-mode
bosonic field interacts with an ensemble of N two-level atoms. This model
exhibits a quantum phase transition in the thermodynamic limit, while for
finite instances the system undergoes a transition from quasi-integrability to
quantum chaotic. We show that the width of the local density of states clearly
points out the imprints of the transition from integrability to chaos but no
trace remains of the quantum phase transition. The connection with the decay of
the fidelity amplitude is also established.Comment: 5 pages, 4 figures, accepted for publication PRE rapid communicatio
Mass sum rules for singly and doubly heavy-flavored hadrons
Regularities in the hadron interaction energies are used to obtain formulas
relating the masses of ground-state hadrons, most of which contain heavy
quarks. Inputs are the constituent quark model, the Feynman-Hellmann theorem,
and the structure of the colormagnetic interaction of QCD. Some of the formulas
can also be obtained from heavy quark effective theory or from
diquark-antiquark supersymmetry. It is argued that the sum rules are more
general than the model from which they are obtained. Where data exist, the
formulas agree quite well with experiment, but most of the sum rules proposed
provide predictions of heavy baryon masses that will be useful for future
measurements.Comment: 13 pages, Plain TeX, no figure
Quasiprobability distribution functions for periodic phase-spaces: I. Theoretical Aspects
An approach featuring -parametrized quasiprobability distribution
functions is developed for situations where a circular topology is observed.
For such an approach, a suitable set of angle-angular momentum coherent states
must be constructed in appropriate fashion.Comment: 13 pages, 3 figure
PREDICTING THE MASSES OF BARYONS CONTAINING ONE OR TWO HEAVY QUARKS
The Feynman-Hellmann theorem and semiempirical mass formulas are used to
predict the masses of baryons containing one or two heavy quarks. In
particular, the mass of the is predicted to be MeV, a
value consistent with measurements.Comment: 11 pages, Plain TeX, 2 figures (not included, available on request
from [email protected]
Band Distributions for Quantum Chaos on the Torus
Band distributions (BDs) are introduced describing quantization in a toral
phase space. A BD is the uniform average of an eigenstate phase-space
probability distribution over a band of toral boundary conditions. A general
explicit expression for the Wigner BD is obtained. It is shown that the Wigner
functions for {\em all} of the band eigenstates can be reproduced from the
Wigner BD. Also, BDs are shown to be closer to classical distributions than
eigenstate distributions. Generalized BDs, associated with sets of adjacent
bands, are used to extend in a natural way the Chern-index characterization of
the classical-quantum correspondence on the torus to arbitrary rational values
of the scaled Planck constant.Comment: 12 REVTEX page
Resonance-assisted tunneling in near-integrable systems
Dynamical tunneling between symmetry related invariant tori is studied in the
near-integrable regime. Using the kicked Harper model as an illustration, we
show that the exponential decay of the wave functions in the classically
forbidden region is modified due to coupling processes that are mediated by
classical resonances. This mechanism leads to a substantial deviation of the
splitting between quasi-degenerate eigenvalues from the purely exponential
decrease with 1 / hbar obtained for the integrable system. A simple
semiclassical framework, which takes into account the effect of the resonance
substructure on the KAM tori, allows to quantitatively reproduce the behavior
of the eigenvalue splittings.Comment: 4 pages, 2 figures, gzipped tar file, to appear in Phys. Rev. Lett,
text slightly condensed compared to first versio
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