496 research outputs found
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
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
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
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
Violation of Ioffe-Regel condition but saturation of resistivity of the high Tc cuprates
We demonstrate that the resistivity data of a number of high Tc cuprates, in
particular La(2-x)SrxCuO4, are consistent with resistivity saturation, although
the Ioffe-Regel condition is strongly violated. By using the f-sum rule
together with calculations of the kinetic energy in the t-J model, we show that
the saturation resistivity is unusually large. This is related to the strong
reduction of the kinetic energy due to strong correlation effects. The
fulfilment of the Ioffe-Regel condition for conventional transition metal
compounds is found to be somewhat accidental.Comment: 4 pages, RevTeX, 2 eps figures, additional material available at
http://www.mpi-stuttgart.mpg.de/andersen/saturation
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
Testing QCD Sum Rule Techniques on the Lattice
Results for the first test of the ``crude'' QCD continuum model, commonly
used in QCD Sum Rule analyses, are presented for baryon correlation functions.
The QCD continuum model is found to effectively account for excited state
contributions to the short-time regime of two-point correlation functions and
allows the isolation of ground state properties. Confusion in the literature
surrounding the physics represented in point-to-point correlation functions is
also addressed. These results justify the use of the ``crude'' QCD continuum
model and lend credence to the results of rigorous QCD Sum Rule analyses.Comment: Discussion of systematic uncertainties augmente
Damping in high-frequency metallic nanomechanical resonators
We have studied damping in polycrystalline Al nanomechanical resonators by
measuring the temperature dependence of their resonance frequency and quality
factor over a temperature range of 0.1 - 4 K. Two regimes are clearly
distinguished with a crossover temperature of 1 K. Below 1 K we observe a
logarithmic temperature dependence of the frequency and linear dependence of
damping that cannot be explained by the existing standard models. We attribute
these phenomena to the effect of the two-level systems characterized by the
unexpectedly long (at least two orders of magnitude longer) relaxation times
and discuss possible microscopic models for such systems. We conclude that the
dynamics of the two-level systems is dominated by their interaction with
one-dimensional phonon modes of the resonators.Comment: 5 pages, 3 figure
Higgs signals and hard photons at the Next Linear Collider: the -fusion channel in the Standard Model
In this paper, we extend the analyses carried out in a previous article for
-fusion to the case of Higgs production via -fusion within the Standard
Model at the Next Linear Collider, in presence of electromagnetic radiation due
real photon emission. Calculations are carried out at tree-level and rates of
the leading order (LO) processes e^+e^-\rightarrow e^+e^- H \ar e^+e^- b\bar b
and e^+e^-\rightarrow e^+e^- H \ar e^+e^- WW \ar e^+e^- \mathrm{jjjj} are
compared to those of the next-to-leading order (NLO) reactions
e^+e^-\rightarrow e^+e^- H (\gamma)\ar e^+e^- b\bar b \gamma and
e^+e^-\rightarrow e^+e^- H (\gamma)\ar e^+e^- WW (\gamma) \ar e^+e^-
\mathrm{jjjj}\gamma, in the case of energetic and isolated photons.Comment: 12 pages, LaTeX, 5 PostScript figures embedded using epsfig and
bitmapped at 100dpi, complete paper including high definition figures
available at ftp://axpa.hep.phy.cam.ac.uk/stefano/cavendish_9611.ps or at
http://www.hep.phy.cam.ac.uk/theory/papers
Smoothing effect and delocalization of interacting Bose-Einstein condensates in random potentials
We theoretically investigate the physics of interacting Bose-Einstein
condensates at equilibrium in a weak (possibly random) potential. We develop a
perturbation approach to derive the condensate wavefunction for an amplitude of
the potential smaller than the chemical potential of the condensate and for an
arbitrary spatial variation scale of the potential. Applying this theory to
disordered potentials, we find in particular that, if the healing length is
smaller than the correlation length of the disorder, the condensate assumes a
delocalized Thomas-Fermi profile. In the opposite situation where the
correlation length is smaller than the healing length, we show that the random
potential can be significantly smoothed and, in the meanfield regime, the
condensate wavefunction can remain delocalized, even for very small correlation
lengths of the disorder.Comment: The word "screening" has been changed to "smoothing" to avoid
confusions with other effects discussed in the literature. This does not
affect the content of paper, nor the results, nor the physical discussio
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