741 research outputs found
Scaling limit of a non-relativistic model
I calculate the structure function for scattering from the two-body bound
state in its lowest level in a non-relativistic model of confined scalar
``quarks'' of masses and . The scaling limit in exists and is non-vanishing only for the values
and which correspond to the fractions of
the momentum of the two-body system carried by each of the ``quarks.'' In the
scaling limit, the interference from scattering off of the two ``quarks''
vanishes. Thus the scaling limit of this model agrees with the parton picture.Comment: 10 pages, 3 figures not included, in LaTex, UMD 92-22
Pentaquark state in pole-dominated QCD sum rules
We propose a new approach in QCD sum rules applied for exotic hadrons with a
number of quarks, exemplifying the pentaquark Theta^{+} (I=0,J=1/2) in the
Borel sum rule. Our approach enables reliable extraction of the pentaquark
properties from the sum rule with good stability in a remarkably wide Borel
window. The appearance of its valid window originates from a favorable setup of
the correlation functions with the aid of it chirality of the interpolating
fields on the analogy of the Weinberg sum rule for the vector currents. Our
setup leads to large suppression of the continuum contributions which have
spoiled the Borel stability in the previous analyses, and consequently enhances
importance of the higher-dimensional contributions of the OPE, which are
indispensable for investigating the pentaquark properties. Implementing the OPE
analysis up to dimension 15, we find that the sum rules for the chiral-even and
odd parts independently give the Theta^{+} mass of 1.68 pm 0.22 GeV with
uncertainties of the condensate values. Our sum rule indeed gives rather flat
Borel curves almost independent of the continuum thresholds both for the mass
and pole residue. Finally, we also discuss possible isolation of the observed
states from the KN scattering state on view of chiral symmetry.Comment: 8 pages, 7 figure
Experimental demonstration of Aharonov-Casher interference in a Josephson junction circuit
A neutral quantum particle with magnetic moment encircling a static electric
charge acquires a quantum mechanical phase (Aharonov-Casher effect). In
superconducting electronics the neutral particle becomes a fluxon that moves
around superconducting islands connected by Josephson junctions. The full
understanding of this effect in systems of many junctions is crucial for the
design of novel quantum circuits. Here we present measurements and quantitative
analysis of fluxon interference patterns in a six Josephson junction chain. In
this multi-junction circuit the fluxon can encircle any combination of charges
on five superconducting islands, resulting in a complex pattern. We compare the
experimental results with predictions of a simplified model that treats fluxons
as independent excitations and with the results of the full diagonalization of
the quantum problem. Our results demonstrate the accuracy of the fluxon
interference description and the quantum coherence of these arrays
Tunable disorder in a crystal of cold polar molecules
In the present work, we demonstrate the possibility of controlling by an
external field the dynamics of collective excitations (excitons) of molecules
on an optical lattice. We show that a suitably chosen two-species mixture of
ultracold polar molecules loaded on an optical lattice forms a phononless
crystal, where exciton-impurity interactions can be controlled by applying an
external electric field. This can be used for the controlled creation of
many-body entangled states of ultracold molecules and the time-domain quantum
simulation of disorder-induced localization and delocalization of quantum
particles
QCD radiative and power corrections and Generalized GDH sum rules
We extend the earlier suggested QCD-motivated model for the -dependence
of the generalized Gerasimov-Drell-Hearn (GDH) sum rule which assumes the
smooth dependence of the structure function , while the sharp dependence
is due to the contribution and is described by the elastic part of the
Burkhardt-Cottingham sum rule. The model successfully predicts the low crossing
point for the proton GDH integral, but is at variance with the recent very
accurate JLAB data. We show that, at this level of accuracy, one should include
the previously neglected radiative and power QCD corrections, as boundary
values for the model. We stress that the GDH integral, when measured with such
a high accuracy achieved by the recent JLAB data, is very sensitive to QCD
power corrections. We estimate the value of these power corrections from the
JLAB data at . The inclusion of all QCD corrections leads
to a good description of proton, neutron and deuteron data at all .Comment: 10 pages, 4 figures (to be published in Physical Review D
Axial anomaly: the modern status
The modern status of the problem of axial anomaly in QED and QCD is reviewed.
Two methods of the derivation of the axial anomaly are presented: 1) by
splitting of coordinates in the expression for the axial current and 2) by
calculation of triangle diagrams, where the anomaly arises from the surface
terms in momentum space. It is demonstrated, that the equivalent formulation of
the anomaly can be given, as a sum rule for the structure function in
dispersion representation of three point function of AVV interaction. It is
argued, that such integral representation of the anomaly has some advantages in
the case of description of the anomaly by contribution of hadronic states in
QCD. The validity of the t'Hooft consistency condition is discussed. Few
examples of the physical application of the axial anomaly are given.Comment: 17 pages, 3 figures, to be published in International Journal of
Modern Physics A, few minor correction were done, two references were adde
The Franke-Gorini-Kossakowski-Lindblad-Sudarshan (FGKLS) Equation for Two-Dimensional Systems
Open quantum systems are, in general, described by a density matrix that is
evolving under transformations belonging to a dynamical semigroup. They can
obey the Franke-Gorini-Kossakowski-Lindblad-Sudarshan (FGKLS) equation. We
exhaustively study the case of a Hilbert space of dimension . First, we find
final fixed states (called pointers) of an evolution of an open system, and we
then obtain a general solution to the FGKLS equation and confirm that it
converges to a pointer. After this, we check that the solution has physical
meaning, i.e., it is Hermitian, positive and has trace equal to , and find a
moment of time starting from which the FGKLS equation can be used - the range
of applicability of the semigroup symmetry. Next, we study the behavior of a
solution for a weak interaction with an environment and make a distinction
between interacting and non-interacting cases. Finally, we prove that there
cannot exist oscillating solutions to the FGKLS equation, which would resemble
the behavior of a closed quantum system.Comment: 27 p.
Entropy-driven phase transition in a polydisperse hard-rods lattice system
We study a system of rods on the 2d square lattice, with hard-core exclusion.
Each rod has a length between 2 and N. We show that, when N is sufficiently
large, and for suitable fugacity, there are several distinct Gibbs states, with
orientational long-range order. This is in sharp contrast with the case N=2
(the monomer-dimer model), for which Heilmann and Lieb proved absence of phase
transition at any fugacity. This is the first example of a pure hard-core
system with phases displaying orientational order, but not translational order;
this is a fundamental characteristic feature of liquid crystals
Bosonic model with fractionalization
Bosonic model with unfrustrated hopping and short-range repulsive interaction
is constructed that realizes fractionalized insulator phase in two
dimensions and in zero magnetic field. Such phase is characterized as having
gapped charged excitations that carry fractional electrical charge 1/3 and also
gapped vortices above the topologically ordered ground state.Comment: 7 pages, 3 figure
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