Neutron--Antineutron Oscillations at the Surface of Nuclei

We discuss some aspects of possible neutron--antineutron oscillations in nuclei. The phenomenon occurs mostly at the surface of nuclei, and hence {\sl i)} is not very sensitive to medium corrections and {\sl ii)} makes use of the antinucleon-nucleus interaction in a region probed by experiments at CERN.Comment: Contr. Oak Ridge Workshop on Workshop on Baryon Instability, Latex, 4 pages, comments to [email protected]

Widths of Ξ\Xi Hypernuclear States

The $\Lambda$ and neutron decay widths of $\Xi$ hypernuclear states, based on calculated \Xi N \to \lala mixing amplitudes, are estimated. The widths which result from using the Nijmegen Model D interaction are sufficiently small, of order 1.5 MeV, that experiments to observe $\Xi$ hypernuclear states using the $(K^-,K^+)$ reaction may be feasible.Comment: 20 pages, LaTex with one postscript figure in accompanying file, to appear in Progress of Theoretical Physics Supplement No. 11

Limits on \boldmath n {\bar n} oscillations from nuclear stability

The relationship between the lower limit on the nuclear stability lifetime as derived from the non disappearance of `stable` nuclei ($T_{d}~\gtrsim~5.4~\times~10^{31}$ yr), and the lower limit thus implied on the oscillation time $(\tau_{n \bar n})$ of a possibly underlying neutron-antineutron oscillation process, is clarified by studying the time evolution of the nuclear decay within a simple model which respects unitarity. The order-of-magnitude result $\tau_{n \bar n} \approx 2 (T_{d}/\Gamma_{\bar n})^{1/2} > 2 \times 10^{8}$ sec, where $\Gamma_{\bar n}$ is a typical $\bar n$ nuclear annihilation width, agrees as expected with the limit on $\tau_{n \bar n}$ established by several detailed nuclear physics calculations, but sharply disagreeing by 15 orders of magnitude with a claim published recently in Phys. Rev. CRAP.Comment: 8 pages; this PRC version (accepted for publication, November 4 1999) differs from the original version only by a few minor editorial change

The influence of strength of hyperon-hyperon interactions on neutron star properties

An equation of state of neutron star matter with strange baryons has been obtained. The effects of the strength of hyperon-hyperon interactions on the equations of state constructed for the chosen parameter sets have been analyzed. Numerous neutron star models show that the appearance of hyperons is connected with the increasing density in neutron star interiors. The performed calculations have indicated that the change of the hyperon-hyperon coupling constants affects the chemical composition of a neutron star. The obtained numerical hyperon star models exclude large population of strange baryons in the star interior.Comment: 18 pages, 22 figures, accepted to be published in Journal of Physics G: Nuclear and Particle Physic

Loosely bound hyperons in the SU(3) Skyrme model

Hyperon pairs bound in deuteron like states are obtained within the SU(3) Skyrme model in agreement with general expectations from boson exchange models. The central binding from the flavor symmetry breaking terms increases with the strangeness contents of the interacting baryons whereas the kinetic non-linear $\sigma$-model term fixes the spin and isospin of the bound pair. We give a complete account of the interactions of octet baryons within the product approximation to baryon number $B=2$ configurations.Comment: 35 pages REVTEX including 2 figs, with 3 further figs available on request from [email protected] or from [email protected] SI-94-TP3S2; STPHY-Th/94-

Rates for the reactions antiproton-proton --> pi phi and gamma phi

We study antiproton-proton annihilation at rest into $\pi\phi$ and $\gamma\phi$. Rescattering by $\overline{K^*}K+K^*\overline{K}$ and $\rho^{+}\rho^{-}$ for $\overline{p}p\rightarrow\pi\phi$ states is sizable, of order $(0.90\, {\rm to}\,2.6)\times 10^{-4}$ in the branching ratio, but smaller than experiment. For $\overline{p}p\rightarrow\gamma\phi$ the rescattering contributions are negligible, but the $\gamma\phi$ channel is well explained by a $\rho\phi$ intermediate state combined with vector meson dominance.Comment: 12 pages, plain latex, 2 postscript figures available upon request, PSI-PR-93-2

Production of Strange Clusters and Strange Matter in Nucleus-Nucleus Collisions at the AGS

Production probabilities for strange clusters and strange matter in Au+Au collisions at AGS energy are obtained in the thermal fireball model. The only parameters of the model, the baryon chemical potential and temperature, were determined from a description of the rather complete set of hadron yields from Si+nucleus collisions at the AGS. For the production of light nuclear fragments and strange clusters the results are similar to recent coalescence model calculations. Strange matter production with baryon number larger than 10 is predicted to be much smaller than any current experimental sensitivities.Comment: 9 Pages (no figures

Model-independent constraints on spin observables

We discuss model-independent constraints on spin observables in exclusive and inclusive reactions, with special attention to the case of photoproduction.Comment: 6 pages, 5 figures, Talk by J.-M. Richard at NSTAR 2009, IHEP, Beijing (China), April 19-22, 2009, Proc. to appear in "Chinese Physics C

Hypernuclei as chiral solitons

The identification of flavored multiskyrmions with the ground states of known hypernuclei is successful for several of them, e.g. for isodoublet H(Lambda) - He(Lambda), A=4, isoscalars He(Lambda) (A=5) and Li(Lambda) (A=7). In other cases agreement is not so good, but the behaviour of the binding energy with increasing baryon number is in qualitative agreement with data. Charmed or beauty hypernuclei within this approach are predicted to be bound stronger than strange hypernuclei. This conclusion is stable against variation of poorly known heavy flavor decay constants.Comment: 9 pages, 1 Fig. Presented at the International Workshops on Nuclear and Particle Physics at 50-Gev PS, NP01 (KEK, Japan, December 2001) and NP02 (Kyoto, Japan, September 2002). Some additions and corrections of numerical results are mad

Neutron Star Constraints on the H Dibaryon

We study the influence of a possible H dibaryon condensate on the equation of state and the overall properties of neutron stars whose population otherwise contains nucleons and hyperons. In particular, we are interested in the question of whether neutron stars and their masses can be used to say anything about the existence and properties of the H dibaryon. We find that the equation of state is softened by the appearance of a dibaryon condensate and can result in a mass plateau for neutron stars. If the limiting neutron star mass is about that of the Hulse-Taylor pulsar a condensate of H dibaryons of vacuum mass 2.2 GeV and a moderately attractive potential in the medium could not be ruled out. On the other hand, if the medium potential were even moderately repulsive, the H, would not likely exist in neutron stars. If neutron stars of about 1.6 solar mass were known to exist, attractive medium effects for the H could be ruled out. Certain ranges of dibaryon mass and potential can be excluded by the mass of the Hulse-Taylor pulsar which we illustrate graphically.Comment: Revised by the addition of a figure showing the region of dibaryon mass and potential excluded by the Hulse-Taylor pulsar. 18 pages, 11 figures, latex (submitted to Phys. Rev. C