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