Explorations of the quark substructure of the nucleon in lattice QCD
Name
720726520-MIT.pdf
Description
Full printable version
Size
14.15 MB
Format
Adobe PDF
Checksum (MD5)
5b49be9f5f052cfd54bad3b2ad3b02b3
Author(s)
Bratt, Jonathan D. (Jonathan Daniel)
Advisor(s)
John W. Negele.
Date Issued
2009
Publisher
Massachusetts Institute of Technology
Abstract
Lattice gauge theory is a valuable tool for understanding how properties of the nucleon arise from the fundamental interactions of QCD. Numerical computations on the lattice can be used not only for first principles calculations of experimentally accessible quantities, but also for calculations of quantities that are not (yet) known from experiment. This thesis presents two lattice studies of the quark substructure of nucleons. The first study used overlaps calculated on the lattice to evaluate the goodness of trial nucleon sources. A variational study was performed to find the trial source that best approximated the true nucleon ground state. In this exploratory work with relatively simple trial sources on quenched lattices, we obtained overlaps as high as 80%. The second study was performed using domain wall valence fermions on Asqtad improved staggered lattices provided by the MILC collaboration, with pion masses as low as 290 MeV. We compute nucleon matrix elements of local quark operators: (F', S'l@P(0) F{Il Dt12 ... i D 0 (0)P, S), where F" E {y", -y"-y, -io*}. These operators are parameterized by generalized form factors, which in the infinite momentum frame can be unambiguously interpreted in terms of Fourier transforms of the transverse spatial distributions of quarks in a nucleon. By calculating the local operators at many different values of nucleon momentum, we extract a complete set of generalized form factors for the lowest two moments of the vector, axial and tensor operators. From the form factors, we compute a variety of quantities characterizing the internal structure of the nucleon. Finally, we explore chiral extrapolations of the lattice results to the physical pion mass.
Description
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 163-166).
Subjects
Physics.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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