622 research outputs found
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
Using personas to promote inclusive education in an online course
Inclusion and diversity are themes at the forefront of education development and the subject of much institutional level policy. However, there are differences that can be made at the course or even module level by local teams that will both compliment institutional policy and have an immediate impact on students. This paper aims to describe the process taken to embed diversity and inclusion into an online career development short course. We will explain how user experience personas, created in the design phase of the course, developed into an integral part of the course curriculum and how they are used to show diversity to a fully asynchronous online cohort. We discuss how theories of pedagogy and design can be combined to have a positive impact on the sense of belong for all students. Finally, we explore how these theories can be applied to wider practice and offer suggestions for how other courses can use our process to embed elements of diversity into their programmes, and hopefully increase a sense of student belonging
Improvement, dynamical fermions, and heavy quark screening in QCD_3
First results from simulations of improved actions for both gauge fields and
staggered fermion fields in three dimensional QCD are presented. This work
provides insight into some issues of relevance to lattice theories in four
dimensions. In particular, the renormalization of the bare lattice coupling is
dramatically reduced when the tree-level improved action is used. Naik
improvement of the staggered fermion action produces little reduction in
scaling violations of the rho meson mass. String breaking in the heavy quark
potential in the unquenched theory is also clearly resolved, using Wilson loops
to bound the ground state energy.Comment: LATTICE98(improvement), 3 pages, 3 figures (psfig format
Baryon structure from Lattice QCD
We present recent lattice results on the baryon spectrum, nucleon
electromagnetic and axial form factors, nucleon to transition form
factors as well as the electromagnetic form factors. The masses of the
low lying baryons and the nucleon form factors are calculated using two
degenerate flavors of twisted mass fermions down to pion mass of about 270 MeV.
We compare to the results of other collaborations. The nucleon to
transition and form factors are calculated in a hybrid scheme, which
uses staggered sea quarks and domain wall valence quarks. The dominant dipole
nucleon to transition form factor is also evaluated using dynamical
domain wall fermions. The transverse density distributions of the in
the infinite momentum frame are extracted using the form factors determined
from lattice QCD.Comment: Invited talk at the Workshop on the Physics of excited nucleons
NSTAR2009, Beijing, April 19-22, 2009, 9 page
Advanced aeronatics design: Project based engineering education at WPI
One element of WPI\u27s project-based curriculum is its interdisciplinary Advanced Aeronautics Design Program. Students participating in the program are involved in the design, construction, and flight testing of non-traditional aircraft such as an ultralight solar-powered vehicle, microwave-powered long endurance aircraft, or a flying oblique wing. The WPI project philosophy and character are described and illustrated using examples from the AAD program
Hadronic Vacuum Polarization Contribution to g-2 from the Lattice
We give a short description of the present situation of lattice QCD
simulations. We then focus on the computation of the anomalous magnetic moment
of the muon using lattice techniques. We demonstrate that by employing improved
observables for the muon anomalous magnetic moment, a significant reduction of
the lattice error can be obtained. This provides a promising scenario that the
accuracy of lattice calculations can match the experimental errors.Comment: Proceedings of the International Workshop on e+e- collisions from Phi
to Psi (PHIPSI11), Sep. 19-22, 2011, BINP, Novosibirsk, Russi
Non-Perturbative Mass Renormalization in Quenched QED from the Worldline Variational Approach
Following Feynman's successful treatment of the polaron problem we apply the
same variational principle to quenched QED in the worldline formulation. New
features arise from the description of fermions by Grassmann trajectories, the
supersymmetry between bosonic and fermionic variables and the much more
singular structure of a renormalizable gauge theory like QED in 3+1 dimensions.
We take as trial action a general retarded quadratic action both for the
bosonic and fermionic degrees of freedom and derive the variational equations
for the corresponding retardation functions. We find a simple analytic,
non-perturbative, solution for the anomalous mass dimension gamma_m(alpha) in
the MS scheme. For small couplings we compare our result with recent four-loop
perturbative calculations while at large couplings we find that gamma_m(alpha)
becomes proportional to (alpha)^(1/2). The anomalous mass dimension shows no
obvious sign of the chiral symmetry breaking observed in calculations based on
the use of Dyson-Schwinger equations, however we find that a perturbative
expansion of gamma_m(alpha) diverges for alpha > 0.7934. Finally, we
investigate the behaviour of gamma_m(alpha) at large orders in perturbation
theory.Comment: 18 pages, 1 Figure, RevTeX; the manuscript has been substantially
revised and enlarged in order to make it selfcontained; accepted for
publication in Phys. Rev.
Gluon Propagator on Coarse Lattices in Laplacian Gauges
The Laplacian gauge is a nonperturbative gauge fixing that reduces to Landau
gauge in the asymptotic limit. Like Landau gauge, it respects Lorentz
invariance, but it is free of Gribov copies; the gauge fixing is unambiguous.
In this paper we study the infrared behavior of the lattice gluon propagator in
Laplacian gauge by using a variety of lattices with spacings from
to 0.35 fm, to explore finite volume and discretization effects. Three
different implementations of the Laplacian gauge are defined and compared. The
Laplacian gauge propagator has already been claimed to be insensitive to finite
volume effects and this is tested on lattices with large volumes.Comment: RevTex 4.0, 14 pages, 9 colour figures; Correction to Reference
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