Soft-pion correction to the Skyrmion, chiral vacuum effects in the bag and double-delta formation in pion absorption

Soft-pion corrections to the Skyrme-soliton are considered to one loop order. Starting from Weinberg's low-energy expansion, a consistent effective description to one-loop order is constructed which contains Skyrme's model in the classical limit. Soft-pion contributions to the nucleon and Δ-isobar masses are evaluated, and their relevance to baryon dynamics discussed. It is shown that under chiral SU(2) x SU(2) boundary conditions of the hedgehog type, the Dirac vacuum in the chiral bag model up non-trivial chiral terms. Double-Δ(1232) formation following pion absorption on heavy nuclei in and above the (3,3) resonance region is compared to the standard πNN→ΔN→NN two-nucleon process. This mechanism is shown to be a substantial, if the ΔN→ΔΔ interactions follows SU(4) quark model rules. It is able to explain some of the striking features observed in proton emission spectra following π/sup +/-/-nucleus absorption in the Δ resonance region. The double-Δ mechanism is further examined in the 4He(π,4N) reaction. It is found that this mechanism contributes appreciably to the total absorption cross section in the energy range of 450-600 MeV