43,140 research outputs found

### Structure Functions, Form Factors, and Lattice QCD

We present results towards the calculation of the pion electric form factor
and structure function on a $16^3\times 24$ lattice using charge overlap. By
sacrificing Fourier transform information in two directions, it is seen that
the longitudinal four point function can be extracted with reasonable error
bars at low momentum.Comment: 3 pages (contribution to "Lattice 93"), UNIX SHAR file includes the
LaTeX source and three encapsulated PS figures (which will print on
appropriate drivers but can not be previewed), BU-HEP-93-0

### Lattice Charge Overlap: Towards the Elastic Limit

A numerical investigation of time-separated charge overlap measurements is
carried out for the pion in the context of lattice QCD using smeared Wilson
fermions. The evolution of the charge distribution function is examined and the
expected asymptotic time behavior $\sim e^{-(E_{q}-m_{\pi})t}$, where $t$
represents the charge density relative time separation, is clearly visible in
the Fourier transform. Values of the pion form factor are extracted using
point-to-smeared correlation functions and are seen to be consistent with the
expected monopole form from vector dominance. The implications of these results
for hadron structure calculations is briefly discussed.Comment: 8 pages, 7 figures appended as ps file

### Disconnected Electromagnetic Form Factors

Preliminary results of a calculation of disconnected nucleon electromagnetic
factors factors on the lattice are presented. The implementation of the
numerical subtraction scheme is outlined. A comparison of results for electric
and magnetic disconnected form factors on two lattice sizes with those of the
Kentucky group is presented. Unlike previous results, the results found in this
calculation are consistent with zero in these sectors.Comment: Lattice 2000 (Hadronic Matrix Elements), 4 pages, 6 fig

### Continuum Moment Equations on the Lattice

An analysis is given as to why one can not directly evaluate continuum moment
equations, i.e., equations involving powers of the position variable times
charge, current, or energy/momentum operators, on the lattice. I examine two
cases: a three point function evaluation of the nucleon magnetic moment and a
four point function (charge overlap) evaluation of the pseudoscalar charge
radius.Comment: 9 pages; 1 ps figur

### Lattice Charge Overlap I: Elastic Limit of Pi and Rho Mesons

Using lattice QCD on a $16^{3}\times 24$ lattice at $\beta=6.0$, we examine
the elastic limit of charge overlap functions in the quenched approximation for
the pion and rho meson; results are compared to previous direct current
insertion calculations. A good signal is seen for the pion, but the electric
and magnetic rho meson results are considerably noisier. We find that the pion
and rho results are characterized by a monopole mass to rho mass ratio of
$0.97(8)$ and $0.73(10)$, respectively. Assuming the functional form of the
electric and magnetic form factors are the same, we also find a rho meson
g-factor of $g=2.25(34)$, consistent with the nonrelativistic quark model.Comment: 19 pages a uuencoded, compressed file (LateX). Uses more
configurations and computes correlated chi-squareds on fits. Figures still
w/o label

### Finite Volume Effects in Self Coupled Geometries

By integrating the pressure equation at the surface of a self coupled
curvilinear boundary, one may obtain asymptotic estimates of energy shifts,
which is especially useful in lattice QCD studies of nonrelativistic bound
states. Energy shift expressions are found for periodic (antiperiodic) boundary
conditions on antipodal points, which require Neumann (Dirichlet) boundary
conditions for even parity states and Dirichlet (Neumann) boundary conditions
for odd parity states. It is found that averaging over periodic and
antiperiodic boundary conditions is an effective way of removing the asymptotic
energy shifts from the boundary. Asymptotic energy shifts from boxes with self
coupled walls are also considered and shown to be effectively antipodal. The
energy shift equations are illustrated by the solution of the bounded harmonic
oscillator and hydrogen atoms.Comment: 17 pages LaTeX, to appear in Ann. Phy

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