643 research outputs found
Chiral Behaviour of the Rho Meson in Lattice QCD
In order to guide the extrapolation of the mass of the rho meson calculated
in lattice QCD with dynamical fermions, we study the contributions to its
self-energy which vary most rapidly as the quark mass approaches zero; from the
processes and . It turns out that in
analysing the most recent data from CP-PACS it is crucial to estimate the
self-energy from using the same grid of discrete momenta as
included implicitly in the lattice simulation. The correction associated with
the continuum, infinite volume limit can then be found by calculating the
corresponding integrals exactly. Our error analysis suggests that a factor of
10 improvement in statistics at the lowest quark mass for which data currently
exists would allow one to determine the physical rho mass to within 5%.
Finally, our analysis throws new light on a long-standing problem with the
J-parameter.Comment: 13 pages, 7 figures. Full analytic forms of the self-energies are
included and a correction in the omega-pi self-energ
Chiral extrapolation of nucleon magnetic form factors
The extrapolation of nucleon magnetic form factors calculated within lattice
QCD is investigated within a framework based upon heavy baryon chiral
effective-field theory. All one-loop graphs are considered at arbitrary
momentum transfer and all octet and decuplet baryons are included in the
intermediate states. Finite range regularisation is applied to improve the
convergence in the quark-mass expansion. At each value of the momentum transfer
(), a separate extrapolation to the physical pion mass is carried out as a
function of alone. Because of the large values of involved, the
role of the pion form factor in the standard pion-loop integrals is also
investigated. The resulting values of the form factors at the physical pion
mass are compared with experimental data as a function of and demonstrate
the utility and accuracy of the chiral extrapolation methods presented herein.Comment: 19 pages, 10 figure
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
Chiral Extrapolations and Exotic Meson Spectrum
We examine the chiral corrections to exotic meson masses calculated in
lattice QCD. In particular, we ask whether the non-linear chiral behavior at
small quark masses, which has been found in other hadronic systems, could lead
to large corrections to the predictions of exotic meson masses based on linear
extrapolations to the chiral limit. We find that our present understanding of
exotic meson decay dynamics suggests that open channels may not make a
significant contribution to such non-linearities whereas the virtual, closed
channels may be important.Comment: 13 pagers, 2 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
Modelling the quark propagator
The quark propagator is at the core of lattice hadron spectrum calculations
as well as studies in other nonperturbative schemes. We investigate the quark
propagator with an improved staggered action (Asqtad) and an improved gluon
action, which provides good quality data down to small quark masses. This is
used to construct ans\"{a}tze suitable for model hadron calculations as well as
adding to our intuitive understanding of QCD.Comment: Lattice2002(spectrum
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
- …