90 research outputs found
Angular Momentum Decomposition for an Electron
We calculate the orbital angular momentum of the `quark' in the scalar
diquark model as well as that of the electron in QED (to order ). We
compare the orbital angular momentum obtained from the Jaffe-Manohar
decomposition to that obtained from the Ji relation and estimate the importance
of the vector potential in the definition of orbital angular momentum
Spin structure of the pion from the instanton vacuum
We investigate the spin structure of the pion within the framework of the
nonlocal chiral quark model from the instanton vacuum. We first evaluate the
tensor form factors of the pion for the first and second moment (n=1,2) and
compare it with the lattice data. Combining the tensor form factor of the pion
with the electromagnetic one, we determine the impact-parameter dependent
probability density of transversely polarized quarks inside the pion. It turns
out that the present numerical results for the tensor form factor as well as
those for the probability density are in good agreement with the lattice data.
We also discuss the distortion of the spatial distribution of the quarks in the
transverse plane inside the pion.Comment: 9 pages, 10 figures, accepted for publication in Phys. Lett.
Renormalization constants of local operators for Wilson type improved fermions
Perturbative and non-perturbative results are presented on the
renormalization constants of the quark field and the vector, axial-vector,
pseudoscalar, scalar and tensor currents. The perturbative computation, carried
out at one-loop level and up to second order in the lattice spacing, is
performed for a fermion action, which includes the clover term and the twisted
mass parameter yielding results that are applicable for unimproved Wilson
fermions, as well as for improved clover and twisted mass fermions. We consider
ten variants of the Symanzik improved gauge action corresponding to ten
different values of the plaquette coefficients. Non-perturbative results are
obtained using the twisted mass Wilson fermion formulation employing two
degenerate dynamical quarks and the tree-level Symanzik improved gluon action.
The simulations are performed for pion masses in the range of 480 MeV to 260
MeV and at three values of the lattice spacing, a, corresponding to beta=3.9,
4.05, 4.20. For each renormalization factor computed non-perturbatively we
subtract its perturbative O(a^2) terms so that we eliminate part of the cut-off
artifacts. The renormalization constants are converted to MS-bar at a scale of
mu=2 GeV. The perturbative results depend on a large number of parameters and
are made easily accessible to the reader by including them in the distribution
package of this paper, as a Mathematica input file.Comment: 36 pages, 11 figures and 6 tables. The results are included in
electronic form (Mathematica files
Minnesota Historical and Cultural Heritage (Legacy) Grant Program: LSA Survey Results and Recommendations
In August 2017, the Legacy Strategic Agenda (LSA) Collaborative Priority Action Team (PAT) for Grants conducted a survey of Minnesota cultural heritage organizations about the Minnesota Historical and Cultural Heritage (Legacy) grant program managed by the Minnesota Historical Society. The presenters will provide a background about the survey and share the results and recommendations that came out of the survey
Legacy Grants: Assessment, Feedback, & Action
Members of the Legacy Strategic Agenda (LSA) Grants Priority Action Team (PAT) will provide an update on the recommendations presented at last year’s MALHM conference. The session will include: A quick overview of our assessment process and the recommendations that were developed Information on how feedback from the 2018 MALHM conference impacted the process Recommendation prioritization and implementation timeline Implementation updates
The session will conclude with an opportunity for attendees to provide additional feedback on the project
Gravitational and higher-order form factors of the pion in chiral quark models
The gravitational form factor of the pion is evaluated in two chiral quark
models and confronted to the recent full-QCD lattice data. We find good
agreement for the case of the Spectral Quark Model, which builds in the
vector-meson dominance for the charge form factor. We derive a simple relation
between the gravitational and electromagnetic form factors, holding in the
considered quark models in the chiral limit. The relation implies that the
gravitational mean squared radius is half the electromagnetic one. We also
analyze higher-order quark generalized form factors of the pion, related to
higher moments in the symmetric Bjorken X-variable of the generalized parton
distribution functions, and discuss their perturbative QCD evolution, needed to
relate the quark-model predictions to the lattice data. The values of the
higher-order quark form factors at t=0, computed on the lattice, also agree
with our quark model results within the statistical and method uncertainties.Comment: 12 pages, 4 figures, discussion and references adde
Moments of generalized parton distributions and quark angular momentum of the nucleon
The internal structure of hadrons is important for a variety of topics,
including the hadron form factors, proton spin and spin asymmetry in polarized
proton scattering.
For a systematic study generalized parton distributions (GPDs) encode
important information on hadron structure in the entire impact parameter space.
We report on a computation of nucleon GPDs based on simulations with two
dynamical non-perturbatively improved Wilson quarks with pion masses down to
350MeV. We present results for the total angular momentum of quarks with chiral
extrapolation based on covariant baryon chiral perturbation theory.Comment: Presented at 25th International Symposium on Lattice Field Theory,
Regensburg, Germany, 30 Jul - 4 Aug 200
Low-Lying Nucleons from Chirally Improved Fermions
We report on our preliminary results on the low-lying excited nucleon spectra
which we obtain through a variational basis formed with three different
interpolators.Comment: Contributed to Lattice 2003(spectrum), Tsukub
The pion mass dependence of the nucleon form-factors of the energy momentum tensor in the chiral quark-soliton model
The nucleon form factors of the energy-momentum tensor are studied in the
large-Nc limit in the framework of the chiral quark-soliton model for model
parameters that simulate physical situations in which pions are heavy. This
allows for a direct comparison to lattice QCD results.Comment: 17 pages, 12 figure
Flavor Twisted Boundary Conditions, Pion Momentum, and the Pion Electromagnetic Form Factor
We investigate the utility of partially twisted boundary conditions in
lattice calculations of meson observables. For dynamical simulations, we show
that the pion dispersion relation is modified by volume effects. In the isospin
limit, we demonstrate that the pion electromagnetic form factor can be computed
on the lattice at continuous values of the momentum transfer. Furthermore, the
finite volume effects are under theoretical control for extraction of the pion
charge radius.Comment: 15 pages, 8 figures, revisions to text, refs adde
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