Recent experimental evidence for the Theta^+(1540) has given rise to much
theoretical interest in exotic baryons. The Theta^+ is a baryon that has
strangeness S=+1, meaning that it contains an anti-strange quark. Thus it
cannot be constructed from three quarks, unlike all other known baryons; it
needs at least an extra quark-antiquark pair. It is usually modeled as a
pentaquark state in the 10 bar representation of flavor SU(3), with flavor
content \bar{s}uudd.
This thesis considers possible heavy pentaquarks, in which the antiquark is
charmed or bottom rather than strange. In the context of the diquark model of
Jaffe and Wilczek, it is argued that negative-parity pentaquarks of this type
may be lighter than their positive-parity counterparts, and hence are likely to
be stable against strong decay. Estimates are made for their masses, and their
weak decays are discussed. Isospin relations are found between the decay rates
for different possible decay channels.
Negative-parity heavy pentaquarks are also considered in a less
model-dependent way, in the context of a 1/N_c expansion, where N_c is the
number of colors. Heavy quark effective theory is also employed. Mass relations
are found between the mass splittings of heavy pentaquarks and those of
nonexotic baryons, and SU(3)-breaking corrections to these relations are
computed. The results could be helpful in interpreting experimental data if
heavy pentaquarks are observed.Comment: PhD thesis; 84 pages, 22 figure
