arXiv subjects

J. L. Goity

Publications and source records attributed to J. L. Goity.

42 records · Page 3Linked to original sources

arXiv1994

Bounds on $ΔB=1$ Couplings in the Supersymmetric Standard Model

The most general supersymmetric model contains baryon number violating terms of the form $λ_{ijk}\;\ov{D}_i\, \ov{D}_j\, \ov{U}_k$ in the superpotential. We reconsider the bounds on these couplings, assuming that lepton number conservation ensures proton stability. These operators can mediate $n - \ov{n}$ oscillations and double nucleon decay. We show that neutron oscillations do not, as previously claimed, constrain the $λ_{dsu}$ coupling; they do provide a bound on the $λ_{dbu}$ coupling, which we calculate. We find that the best bound on $λ_{dsu}$ 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.

hep-ph↗

arXiv1994

Soft Pion Emission in Semileptonic $B$-Meson Decays

An analysis of semileptonic decays of $B$ mesons with the emission of a single soft pion is presented in the framework of the heavy-quark limit using an effective Lagrangian which implements chiral and heavy-quark symmetries. The analysis is performed at leading order of the chiral and inverse heavy mass expansions. In addition to the ground state heavy mesons some of their resonances are included. The estimates of the various effective coupling constants and form factors needed in the analysis are obtained using a chiral quark model. As the main result, a clear indication is found that the $0^{+}$ and $1^{+}$ resonances substantially affect the decay mode with a $D^{\ast}$ in the final state, and a less dramatic effect is also noticed in the $D$ mode. An analysis of the decay spectrum in the $D^{(\ast)}-π$ squared invariant mass is carried out, showing the main effects of including the resonances. The obtained rates show promising prospects for studies of soft pion emission in semileptonic $B$-meson decays in a $B$-meson factory where, modulo experimental cuts, about $10^5$ such decays in the $D$ meson mode and $10^4$ in the $D^{\ast}$ mode could be observed per year.

hep-ph↗

arXiv1993

Chemical Relaxation Times in a Hadron Gas at Finite Temperature

The relaxation times of particle numbers in hot hadronic matter with vanishing baryon number are estimated using the ideal gas approximation and taking into account resonance decays and annihilation processes as the only sources of particle number fluctuations. Near the QCD critical temperature the longest relaxation times turn out to be of the order of 10 fm and grow roughly exponentially to become of the order of $10^{3}$ fm at temperatures around 100 MeV. As a consequence of such long relaxation times, a clear departure from chemical equilibrium must be observed in the momentum distribution of secondary particles produced in high energy nuclear collisions.

hep-ph↗

arXiv1993

Production, Collection and Utilization of Very Long-Lived Heavy Charged Leptons

If a fourth generation of leptons exists, both the neutrino and its charged partner must be heavier than 45 GeV. We suppose that the neutrino is the heavier of the two, and that a global or discrete symmetry prohibits intergenerational mixing. In that case, non-renormalizable Planck scale interactions will induce a very small mixing; dimension five interactions will lead to a lifetime for the heavy charged lepton of $O(1-100)$ years. Production of such particles is discussed, and it is shown that a few thousands can be produced and collected at a linear collider. The possible uses of these heavy leptons is also briefly discussed.

hep-ph↗

arXiv1992

Electromagnetic Mass Splittings in Heavy Mesons

The electromagnetic contribution to the isomultiplet mass splittings of heavy mesons is reanalyzed within the framework of the heavy mass expansion. It is shown that the leading term in the expansion is given to a good approximation by the elastic term. $1/m_{Q}$-corrections can only be estimated, the main source of uncertainty now being inelastic contributions. The $1/m_{Q}$-corrections to the elastic term turn out to be relatively small in both D and B pseudoscalar mesons.

hep-ph↗

arXiv1992

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 ($F_{D}, F_{D_{s}}$) and the form factor for semileptonic $\overline{B}\rightarrow D^{(\ast)} l\barν_{l}$ 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 non-analytic correction to the mass splittings of ${\cal O}(p^3)$ appears, similar the the one found in light baryons. The correction to $F_{D_{s}}/F_{D}$ 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.

hep-ph↗