Delta Excitation Calculation Studies in Compressed Finite Spherical Nucleus ^(40)Ca

With an oscillator basis,the nuclear Hamiltonian is defined in a no-core model space.It consists of an effective nucleon-nucleon interaction obtained with Brueckner theory from the Reid soft core interaction,a Coulomb potential,nucleon-delta transition potentials,and delta-delta interaction terms.By performing spherical Hartree-Fock(SHF) calculations with the realistic baryon Hamiltonian,the ground state properties of 40Ca are studied.For an estimate of how the delta degree of freedom is excited,SHF calculations are performed with a radial constraint to compress the nucleus.The delta degree of freedom is gradually populated as the nucleus is compressed.The number of Δ's is decreased by increasing model space.Large amount of the compressive energy is delivered to create massive Δ in the nucleus.There is a significant reduction in the static compression modulus for RSC static compressions which is reduced by including the Δ excitations.The static compression modulus is decreased significantly by en larging the nucleon model space.The results suggest that inclusion of the delta in the nuclear dynamics could head to a significant softening of the nuclear equation of state.