Jose L. Goity

Bounds on {Delta}B = 1 couplings in the supersymmetric standard model

The most general supersymmetric model contains baryon number violating terms of the form {lambda}{sub ijk} {bar D}{sub i}{bar D}{sub j}{bar U}{sub k} in the superpotential. The authors reconsider the bounds on these couplings, assuming that lepton number conservation ensures proton stability. These operators can mediate n-{anti n} oscillations and double nucleon decay. They show that neutron oscillations do not, as previously claimed, constrain the {lambda}{sub dsu} coupling; they do provide a bound on the {lambda}{sub dbu} coupling, which they calculate. They find that the best bound on {lambda}{sub dsu} arises from double nucleon decay into two kaons; the calculation is discussed in detail. There are no published limits on this process; experimenters are urged to examine this nuclear decay mode. Finally, the other couplings can be bounded by the requirement of perturbative unification.

Masses of the 70- baryons in large Nc QCD

The masses of the negative parity 70-plet baryons are analyzed in large N(c) QCD to order 1/N(c) and to first order in SU(3) symmetry breaking. The existing experimental data are well reproduced and 20 new observables are predicted. The leading order SU(6) spin-flavor symmetry breaking is small and, as it occurs in the quark model, the subleading in 1/N(c) hyperfine interaction is the dominant source of the breaking. It is found that the Lambda(1405) and Lambda(1520) are well described as three-quark states and spin-orbit partners. New relations between splittings in different SU(3) multiplets are found.

Chiral perturbation theory for SU(3) breaking in heavy-meson systems

The SU(3)-breaking effects due to light-quark masses on heavy-meson masses, decay constants ({ital F}{sub {ital D}},{ital F}{sub {ital D}{ital s}}), and the form factor for semileptonic {ital {bar B}}{r arrow}{ital D}{sup (*)}{ital l}{bar {nu}}{sub {ital l}} transitions are formulated in chiral perturbation theory, using a heavy-meson effective Lagrangian and expanding in inverse powers of the heavy-meson mass. To leading order in this expansion, the leading chiral logarithms and the required counterterms are determined. At this level, a nonanalytic correction to the mass splittings of {ital O}({ital p}{sup 3}) appears, similar to the one found in light baryons. The correction to {ital F}{sub {ital D}{ital s}}/{ital F}{sub {ital D}} is roughly estimated to be of the order of 10% and, therefore, experimentally accessible, while the correction to the form factor is likely to be substantially smaller. We explicitly check that the heavy-quark symmetry is preserved by the chiral loops.

Operator analysis of L=1 baryon masses in large N{sub c} QCD

The authors consider in detail the mass operator analysis for the nonstrange L=1 excited baryons in large N{sub c} QCD. They present a straightforward procedure for constructing the large N{sub c} baryon wavefunctions, and provide complete analytic expressions for the matrix elements of all the independent isosinglet mass operators. They discuss the relationship between the old-fashioned operator analyses based on nonrelativistic SU(6) symmetry and the modern large N{sub c} approach, which has a firmer theoretical foundation. They then suggest a possible dynamical interpretation for the subset of operators preferred strongly by the data.

Nc limit of spin-flavor breaking in excited baryon levels

Spin-flavor symmetry breaking in the levels of excited Baryons are studied to leading order in the 1/N{sub c} expansion. This breaking occurs at zeroth order. For non-strange Baryons with a single quark excited, it is shown that to first order of perturbation theory the breaking is given by one 1-body operator (spin-orbit), and three 2-body operators, all involving the orbital angular momentum of the excited quark. Higher-body operators can be reduced to that set of operators. As illustration, p-wave Baryons are briefly discussed.

Negative Parity 70-plet Baryon Masses in the 1/N{sub c} Expansion

The masses of the negative parity

Masses of orbitally excited baryons in large Nc QCD

\mathrm{SU}(6)

Analysis of the [56,2+] baryon masses in the 1/Nc expansion

70-plet baryons are analyzed in the

Radiative transitions in heavy mesons in a relativistic quark model

{1/N}_{c}

Soft pion emission in semileptonic B-meson decays.

expansion to order