47,325 research outputs found
Chiral extrapolation and physical insights
It has recently been established that finite-range regularisation in chiral
effective field theory enables the accurate extrapolation of modern lattice QCD
results to the chiral regime. We review some of the highlights of
extrapolations of quenched lattice QCD results, including spectroscopy and
magnetic moments. The resonance displays peculiar chiral features in
the quenched theory which can be exploited to demonstrate the presence of
significant chiral corrections.Comment: 6 pages, 5 figures, presented at LHP2003, Cairns, Australi
Hadron structure on the back of an envelope
In order to remove a little of the mysticism surrounding the issue of
strangeness in the nucleon, we present simple, physically transparent estimates
of both the strange magnetic moment and charge radius of the proton. Although
simple, the estimates are in quite good agreement with sophisticated
calculations using the latest input from lattice QCD. We further explore the
possible size of systematic uncertainties associated with charge symmetry
violation (CSV) in the recent precise determination of the strange magnetic
moment of the proton. We find that CSV acts to increase the error estimate by
0.003 \mu_N such that G_M^s = -0.046 +/- 0.022 \mu_N.Comment: 9 pages, 1 figure, Invited talk at First Workshop on Quark-Hadron
Duality and the Transition to pQCD, Frascati, June 6-8 200
Chiral Symmetry and the Intrinsic Structure of the Nucleon
Understanding hadron structure within the framework of QCD is an extremely
challenging problem. In order to solve it, it is vital that our thinking should
be guided by the best available insight. Our purpose here is to explain the
model independent consequences of the approximate chiral symmetry of QCD for
two famous results concerning the structure of the nucleon. We show that both
the apparent success of the constituent quark model in reproducing the ratio of
the proton to neutron magnetic moments and the apparent success of the Foldy
term in reproducing the observed charge radius of the neutron are coincidental.
That is, a relatively small change of the current quark mass would spoil both
results.Comment: RevTeX, 10 pages, 2 figure
Extrapolation of lattice QCD results beyond the power-counting regime
Resummation of the chiral expansion is necessary to make accurate contact
with current lattice simulation results of full QCD. Resummation techniques
including relativistic formulations of chiral effective field theory and
finite-range regularization (FRR) techniques are reviewed, with an emphasis on
using lattice simulation results to constrain the parameters of the chiral
expansion. We illustrate how the chiral extrapolation problem has been solved
and use FRR techniques to identify the power-counting regime (PCR) of chiral
perturbation theory. To fourth-order in the expansion at the 1% tolerance
level, we find 0 \le m_pi \le 0.18 GeV for the PCR, extending only a small
distance beyond the physical pion mass.Comment: 12 pages, 5 figures, plenary talk at BARYONS 2004, Paris, Oct. 25-2
Extracting nucleon strange and anapole form factors from world data
The complete world set of parity violating electron scattering data up to
Q^2~0.3 GeV^2 is analysed. We extract the current experimental determination of
the strange electric and magnetic form factors of the proton, as well as the
weak axial form factors of the proton and neutron, at Q^2 = 0.1 GeV^2. Within
experimental uncertainties, we find that the strange form factors are
consistent with zero, as are the anapole contributions to the axial form
factors. Nevertheless, the correlation between the strange and anapole
contributions suggest that there is only a small probability that these form
factors all vanish simultaneously.Comment: 4 pages, 3 figs; v2: version to appear in PR
Chiral and Continuum Extrapolation of Partially-Quenched Lattice Results
The vector meson mass is extracted from a large sample of partially quenched,
two-flavor lattice QCD simulations. For the first time, discretisation,
finite-volume and partial quenching artefacts are treated in a unified
framework which is consistent with the low-energy behaviour of QCD. This
analysis incorporates the leading infrared behaviour dictated by chiral
effective field theory. As the two-pion decay channel cannot be described by a
low-energy expansion alone, a highly-constrained model for the decay channel of
the rho-meson is introduced. The latter is essential for extrapolating lattice
results from the quark-mass regime where the rho is observed to be a physical
bound state.Comment: 9 pages, 3 figures; revised version appearing in PL
Chiral and Continuum Extrapolation of Partially-Quenched Hadron Masses
Using the finite-range regularisation (FRR) of chiral effective field theory,
the chiral extrapolation formula for the vector meson mass is derived for the
case of partially-quenched QCD. We re-analyse the dynamical fermion QCD data
for the vector meson mass from the CP-PACS collaboration. A global fit,
including finite lattice spacing effects, of all 16 of their ensembles is
performed. We study the FRR method together with a naive polynomial approach
and find excellent agreement ~1% with the experimental value of M_rho from the
former approach. These results are extended to the case of the nucleon mass.Comment: 6 pages, Contribution to Lattice2005, PoS styl
Coping with Poorly Understood Domains: the Example of Internet Trust
The notion of trust, as required for secure operations over the Internet, is important for ascertaining the source of received messages. How can we measure the degree of trust in authenticating the source? Knowledge in the domain is not established, so knowledge engineering becomes knowledge generation rather than mere acquisition. Special techniques are required, and special features of KBS software become more important than in conventional domains. This paper generalizes from experience with Internet trust to discuss some techniques and software features that are important for poorly understood domains
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