18,998 research outputs found
The Sigma Commutator from Lattice QCD
As a direct source of information on chiral symmetry breaking within QCD, the
sigma commutator is of considerable importance. Since hadron structure is a
non-perturbative problem, numerical calculations on a space-time lattice are
currently the only rigorous approach. With recent advances in the calculation
of hadron masses within full QCD, it is of interest to see whether the sigma
commutator can be calculated directly from the dependence of the nucleon mass
on the input quark mass. We show that, provided the correct chiral behaviour of
QCD is respected in the extrapolation to realistic quark masses, one can indeed
obtain a fairly reliable determination of the sigma commutator using present
lattice data. For two-flavour dynamical fermion QCD the sigma commutator lies
between 45 and 55 MeV based on recent data from CP-PACS and UKQCD.Comment: 4 pages, 3 figures, uses espcrc1.sty and epsfig.sty. Contribution to
the proceedings of the International Conference on Quark Nuclear Physics held
in Adelaide Feb. 200
Cryogenic Data Center Activities Semiannual Progress Report, 1 Jan. - 30 Jun. 1966
Activities of Data Compilation and Documentation unit
Chiral Nonanalytic Behaviour: The Edinburgh Plot
The Edinburgh Plot is a scale independent way of presenting lattice QCD
calculations over a wide range of quark masses. In this sense it is appealing
as an indicator of how the approach to physical quark masses is progressing.
The difficulty remains that even the most state of the art calculations are
still at quark masses that are too heavy to apply dimensionally-regulated
chiral perturbation theory. We present a method allowing predictions of the
behaviour of the Edinburgh plot, in both the continuum, and on the lattice.Comment: 3 pages, 4 figures, Lattice2002(Spectrum
Archimedean-type force in a cosmic dark fluid: II. Qualitative and numerical study of a multistage Universe expansion
In this (second) part of the work we present the results of numerical and
qualitative analysis, based on a new model of the Archimedean-type interaction
between dark matter and dark energy. The Archimedean-type force is linear in
the four-gradient of the dark energy pressure and plays a role of
self-regulator of the energy redistribution in a cosmic dark fluid. Because of
the Archimedean-type interaction the cosmological evolution is shown to have a
multistage character. Depending on the choice of the values of the model
guiding parameters,the Universe's expansion is shown to be perpetually
accelerated, periodic or quasiperiodic with finite number of
deceleration/acceleration epochs. We distinguished the models, which can be
definitely characterized by the inflation in the early Universe, by the
late-time accelerated expansion and nonsingular behavior in intermediate
epochs, and classified them with respect to a number of transition points.
Transition points appear, when the acceleration parameter changes the sign,
providing the natural partition of the Universe's history into epochs of
accelerated and decelerated expansion. The strategy and results of numerical
calculations are advocated by the qualitative analysis of the instantaneous
phase portraits of the dynamic system associated with the key equation for the
dark energy pressure evolution.Comment: 15 pages, 12 figures, Part II, typos corrected, Fig.4 replaced,
references correcte
Adiabatic Compressibility of Electrolytic Solutions and the X-Ray Diffraction Intensity Distributions
A study of the adiabatic compressibility and the X-ray diffraction intensity distributions of twenty-six strong electrolytes shows a correlation to the following extent. If one compares the rate of change of adiabatic compressibility per mole with the rate of change of the minor X-ray diffraction peak per mole in two thirds of the twenty-six samples these values increase in magnitude together. If one plots the values of the former, changing from one to eight times, and of the latter varying sixty times, the points are included within an angle of about 35° (with one exception). This approximate correspondence adds credence to the view-obtained on other grounds, that the water structure alters by the breaking of H bonds and that this is the chief cause of the variations in the adiabatic compressibility
Baryon Mass Extrapolation
Consideration of the analytical properties of pion-induced baryon
self-energies leads to new functional forms for the extrapolation of light
baryon masses. These functional forms reproduce the leading non-analytic
behavior of chiral perturbation theory, the correct heavy-quark limit and have
the advantage of containing information on the extended structure of hadrons.
The forms involve only three unknown parameters which may be optimized by
fitting to present lattice data. Recent dynamical fermion results from CP-PACS
and UK-QCD are extrapolated using these new functional forms. We also use these
functions to probe the limit of the chiral perturbative regime and shed light
on the applicability of chiral perturbation theory to the extrapolation of
present lattice QCD results.Comment: LATTICE99 (QCD Spectrum and Quark Masses
Chiral Corrections to Baryon Masses Calculated within Lattice QCD
Consideration of the analytic properties of pion-induced baryon self energies
leads to new functional forms for the extrapolation of light baryon masses.
These functional forms reproduce the leading non-analytic behavior of chiral
perturbation theory, the correct non-analytic behavior at the threshold
and the appropriate heavy-quark limit. They involve only three unknown
parameters, which may be obtained by fitting lattice QCD data. Recent dynamical
fermion results from CP-PACS and UKQCD are extrapolated using these new
functional forms. We also use these functions to probe the limit of
applicability of chiral perturbation theory.Comment: 4 pages, 2 figures, Contribution to the Proceedings of the 15th
Particles and Nuclei International Conference (PANIC 99), Uppsala, Sweden,
June 10-16, 199
A Note on the Instability of Lorentzian Taub-NUT-Space
I show that there are no SU(2)-invariant (time-dependent) tensorial
perturbations of Lorentzian Taub-NUT space. It follows that the spacetime is
unstable at the linear level against generic perturbations. I speculate that
this fact is responsible for so far unsuccessful attempts to define a sensible
thermodynamics for NUT-charged spacetimes.Comment: 13 pages, no figure
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