1,711 research outputs found
Sigma terms from an SU(3) chiral extrapolation
We report a new analysis of lattice simulation results for octet baryon
masses in 2+1-flavor QCD, with an emphasis on a precise determination of the
strangeness nucleon sigma term. A controlled chiral extrapolation of a recent
PACS-CS Collaboration data set yields baryon masses which exhibit remarkable
agreement both with experimental values at the physical point and with the
results of independent lattice QCD simulations at unphysical meson masses.
Using the Feynman-Hellmann relation, we evaluate sigma commutators for all
octet baryons. The small statistical uncertainty, and considerably smaller
model-dependence, allows a signifcantly more precise determination of the
pion-nucleon sigma commutator and the strangeness sigma term than hitherto
possible, namely {\sigma}{\pi}N=45 \pm 6 MeV and {\sigma}s = 21 \pm 6 MeV at
the physical point.Comment: 4 pages, 4 figure
Progress in resolving charge symmetry violation in nucleon structure
Recent work unambiguously resolves the level of charge symmetry violation in
moments of parton distributions using 2+1-flavor lattice QCD. We introduce the
methods used for that analysis by applying them to determine the strong
contribution to the proton-neutron mass difference. We also summarize related
work which reveals that the fraction of baryon spin which is carried by the
quarks is in fact structure-dependent rather than universal across the baryon
octet.Comment: 8 pages, 4 figures; presented at "The Seventh International Symposium
on Chiral Symmetry in Hadrons and Nuclei", BeiHang Univ. Beijing, Chin
Updated Analysis of the Mass of the H Dibaryon from Lattice QCD
Recent lattice QCD calculations from the HAL and NPLQCD Collaborations have
reported evidence for the existence of a bound state with strangeness -2 and
baryon number 2 at quark masses somewhat higher than the physical values. A
controlled chiral extrapolation of these lattice results to the physical point
suggested that the state, identified with the famed H dibaryon, is most likely
slightly unbound (by 13 14 MeV) with respect to the
threshold. We report the results of an updated analysis which finds the H
unbound by 26 11 MeV. Apart from the insight it would give us into how
QCD is realized in Nature, the H is of great interest because of its potential
implications for the equation of state of dense matter and studies of neutron
stars. It may also explain the enhancement above the
threshold already reported experimentally. It is clearly of great importance
that the latter be pursued in experiments at the new J-PARC facility.Comment: Invited presentation at APPC12 (12th Asia Pacific Physics
Conference), July 14-19, 2013, Chiba, Japa
System f2lp – computing answer sets of first-order formulas
Abstract. We present an implementation of the general language of stable models proposed by Ferraris, Lee and Lifschitz. Under certain conditions, system f2lp turns a first-order theory under the stable model semantics into an answer set program, so that existing answer set solvers can be used for computing the general language. Quantifiers are first eliminated and then the resulting quantifier-free formulas are turned into rules. Based on the relationship between stable models and circumscription, f2lp can also serve as a reasoning engine for general circumscriptive theories. We illustrate how to use f2lp to compute the circumscriptive event calculus.
Off-forward gluonic structure of vector mesons
United States. Department of Energy (DE-SC0010495)United States. Department of Energy (DE-SC0011090
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