Equivalence of model space techniques and the renormalization group for a separable model problem

Lee-Suzuki similarity transformations and Krencigowa-Kuo folded diagrams are two common methods used to derive energy independent model space effective interactions for nuclear many-body systems. We demonstrate that these methods are equivalent to a Renormalization Group (RG) analysis of a separable potential model. The effective low-momentum potentials V_{eff} are shown to give the same scaling equation that RG arguments predict. We find the new result that the different model space techniques considered in this paper yield a unique low-momentum V_{eff} when applied to the toy model problem.Comment: 10 pages. Minor content and stylistic change

Antikaons and hyperons in nuclear matter with saturation

We evaluate the antikaon and hyperon spectral functions in a self-consistent and covariant many-body approach. The computation is based on coupled-channel dynamics derived from the chiral SU(3) Lagrangian. A novel subtraction scheme is developed that avoids kinematical singularities and medium-induced power divergencies all together. Scalar and vector mean fields are used to model nuclear binding and saturation. The effect of the latter is striking for the antikaon spectral function that becomes significantly more narrow at small momenta. Attractive mass shifts of about 30 and 40 MeV are predicted for the Lambda(1405) and Sigma(1385) resonances. Once scalar and vector mean fields for the nucleon are switched on the Lambda(1520) resonances dissolves almost completely in nuclear matter. All together only moderate attraction is predicted for the nuclear antikaon systems at saturation density. However, at larger densities we predict a sizable population of soft antikaon modes that arise from the coupling of the antikaon to a highly collective Lambda(1115) nucleon-hole state. This may lead to the formation of exotic nuclear systems with strangeness and antikaon condensation in compact stars at moderate densities.Comment: 49 pages, 13 figures, The revised manuscript contains additional material at twice nuclear saturation density. An unexpected and novel mechanism is unravelled that may have dramatic implications on the formation of exotic nuclear systems with strangeness and antikaon condensation in compact star

On the role of the Δ(1232)\Delta (1232) on the transverse nuclear response in the (e,e′)(e,e') reaction

The transverse nuclear response to an electromagnetic probe which is limited to create (or destroyed) a particle-hole ($ph$) or delta-hole ($\Delta h$) pair is analyzed. Correlations of the random phase approximation (RPA) type and self energy insertions are considered. For RPA correlations we have developed a scheme which includes explicitly the $\Delta$ and the exchange terms. Self energy insertions over $ph$ and $\Delta h$ bubbles are studied. Several residual interactions based on a contact plus a ($\pi + \rho$)-meson exchange potential are used. All calculations are performed in non-relativistic nuclear matter. The main effect of the $\Delta$ is to reduce the intensity over the nuclear quasi-elastic peak. Exchange RPA terms are very important, while the self energy depends strongly on the residual interaction employed. We compare our final result with data for $^{40}Ca$ at momentum transfer $q=410$ and $q=550$ MeV/c.Comment: 42 pages, 18 Postscript figure