Radhey Shyam

Photoproduction of hypernuclei within the quark–meson coupling model

Abstract We study the photoproduction of the 12ΛB hypernucleus within a fully covariant effective Lagrangian based model, employing Λ bound state spinors derived from the latest quark–meson coupling model. The kaon production vertex is described via creation, propagation and decay of N ∗ ( 1650 ) , N ∗ ( 1710 ) , and N ∗ ( 1720 ) intermediate baryonic resonant states in the initial collision of the photon with a target proton in the incident channel. The parameters of the resonance vertices are fixed by describing the total and differential cross section data on the elementary γ p → Λ K + reaction in the energy regime relevant to the hypernuclear production. It is found that the hypernuclear production cross sections calculated with the quark model based hyperon bound state spinors differ significantly from those obtained with the phenomenological Dirac single particle wave functions.

Dilepton production in nucleon-nucleon collisions reexamined

We present a fully relativistic and gauge-invariant framework for calculating the cross sections of dilepton production in nucleon-nucleon (NN) collisions that is based on the meson-exchange approximation for the NN-scattering amplitudes. Predictions of our model are compared with those of other covariant models that have been used earlier to describe this reaction. Our results are also compared with those of the semiclassical models that are employed to get the input elementary cross sections in the transport model calculations of the dilepton production in nucleus-nucleus collisions. It is found that cross sections obtained within the semiclassical and quantum mechanical models differ noticeably from each other.

BINDING OF HYPERNUCLEI, AND PHOTOPRODUCTION OF Λ-HYPERNUCLEI IN THE LATEST QUARK-MESON COUPLING MODEL

We study the binding of hypernuclei based on the latest version of quark-meson coupling model, and estimate the photoproduction cross sections for the reaction using the bound Λ spinors obtained in the model.

Double-Λ hypernuclei within a Skyrme–Hartree–Fock approach

We extend our Skyrme–Hartree–Fock (SHF) approach, which was used earlier to describe successfully the single-Λ hypernuclei, to investigate the binding and the ΛΛ bond energies of the double-Λ hypernuclei. The nucleon–nucleon (NN) and Λ-nucleon (ΛN) interactions are taken from our previous study. For the ΛΛ force, several Skyrme-like potentials available in the literature have been used. We discuss the sensitivity of the calculated ΛΛ binding and bond energies to the ΛΛ and ΛN force parameters. It is found that the existing ΛΛ hypernuclear data do not allow to distinguish between various ΛΛ force parameter sets used by us. However, they show some selectivity for a particular set of the ΛN potential determined in our previous work.

Magnetic moment of the deuteron and nucleon--nucleon spin-orbit potentials

The change in the magnetic moment of the deutcron arising from the presence of the spin-orbit potential in the nucleon-nucleon interaction has been estimated for the Yala, Hamada-Johnston, and Reid potentials. The present estimates are more close to experimect than those obtained previously from some old fashioned potentials. (auth)