78,414 research outputs found
Interplay of Spin and Orbital Angular Momentum in the Proton
We derive the consequences of the Myhrer-Thomas explanation of the proton
spin problem for the distribution of orbital angular momentum on the valence
and sea quarks. After QCD evolution these results are found to be in very good
agreement with both recent lattice QCD calculations and the experimental
constraints from Hermes and JLab
Pure sea-quark contributions to the magnetic form factors of baryons
We propose the pure sea-quark contributions to the magnetic form factors of
baryons, and , as priority
observables for the examination of sea-quark contributions to baryon structure,
both in present lattice QCD simulations and possible future experimental
measurement. , the -quark contribution to the magnetic form
factor of , and , the -quark contribution to the
magnetic form factor of , are similar to the strange quark
contribution to the magnetic form factor of the nucleon, but promise to be
larger by an order of magnitude. We explore the size of this quantity within
chiral effective field theory, including both octet and decuplet intermediate
states. The finite range regularization approach is applied to deal with
ultraviolet divergences. Drawing on an established connection between quenched
and full QCD, this approach makes it possible to predict the sea quark
contribution to the magnetic form factor purely from the meson loop. In the
familiar convention where the quark charge is set to unity . We find a value of , which is
about seven times larger than the strange magnetic moment of the nucleon found
in the same approach. Including quark charge factors, the -quark
contribution to the magnetic moment exceeds the strange quark
contribution to the nucleon magnetic moment by a factor of 14.Comment: 5 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1312.337
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
Decoherence of spin echoes
We define a quantity, the so-called purity fidelity, which measures the rate
of dynamical irreversibility due to decoherence, observed e.g in echo
experiments, in the presence of an arbitrary small perturbation of the total
(system + environment) Hamiltonian. We derive a linear response formula for the
purity fidelity in terms of integrated time correlation functions of the
perturbation. Our relation predicts, similarly to the case of fidelity decay,
faster decay of purity fidelity the slower decay of time correlations is. In
particular, we find exponential decay in quantum mixing regime and faster,
initially quadratic and later typically gaussian decay in the regime of
non-ergodic, e.g. integrable quantum dynamics. We illustrate our approach by an
analytical calculation and numerical experiments in the Ising spin 1/2 chain
kicked with tilted homogeneous magnetic field where part of the chain is
interpreted as a system under observation and part as an environment.Comment: 22 pages, 10 figure
Liquid-gas phase transition in nuclear matter including strangeness
We apply the chiral SU(3) quark mean field model to study the properties of
strange hadronic matter at finite temperature. The liquid-gas phase transition
is studied as a function of the strangeness fraction. The pressure of the
system cannot remain constant during the phase transition, since there are two
independent conserved charges (baryon and strangeness number). In a range of
temperatures around 15 MeV (precise values depending on the model used) the
equation of state exhibits multiple bifurcates. The difference in the
strangeness fraction between the liquid and gas phases is small when they
coexist. The critical temperature of strange matter turns out to be a
non-trivial function of the strangeness fraction.Comment: 15 pages, 7 figure
Towards a Connection Between Nuclear Structure and QCD
As we search for an ever deeper understanding of the structure of hadronic
matter one of the most fundamental questions is whether or not one can make a
connection to the underlying theory of the strong interaction, QCD. We build on
recent advances in the chiral extrapolation problem linking lattice QCD at
relatively large ``light quark'' masses to the physical world to estimate the
scalar polarizability of the nucleon. The latter plays a key role in modern
relativistic mean-field descriptions of nuclei and nuclear matter (such as QMC)
and, in particular, leads to a very natural saturation mechanism. We
demonstrate that the value of the scalar polarizability extracted from the
lattice data is consistent with that needed for a successful description of
nuclei within the framework of QMC. In a very real sense this is the first hint
of a direct connection between QCD and the properties of finite nuclei.Comment: Lecture presented at: 18th Nishinomiya-Yukawa Memorial Symposium On
Strangeness In Nuclear Matter : 4-5 Dec 2003, Nishinomiya, Japa
Neutron stars and strange stars in the chiral SU(3) quark mean field model
We investigate the equations of state for pure neutron matter and strange
hadronic matter in -equilibrium, including , and
hyperons. The masses and radii of pure neutron stars and strange hadronic stars
are obtained. For a pure neutron star, the maximum mass is about , while for a strange hadronic star, the maximum mass is
around . The typical radii of pure neutron stars and
strange hadronic stars are about 11.0-12.3 km and 10.7-11.7 km, respectively.Comment: 18 pages, 7 figure
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
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