Spin-isospin Excitations Research Articles

Pion condensation in symmetric nuclear matter

The problem of pion condensation in isospin symmetric nuclear matter is investigated in the framework of the σ-model with a residual nucleon-nucleon interaction ( g′ σ 1 · σ 2 τ 1 · τ 2 δ( x)) and Δ-isobars. The equation of state for the pion condensed phase is calculated and applied to a low-energy heavy-ion collision in the TDHF approximation. The effective particle-hole interaction and the response to spin-isospin excitation are used to determine the magnitude of the Landau-Migdal parameter g′. For a reasonable range of g′(0.5 < g′ ≦ in units of g 2/4 m 2 N = 410 MeV · fm 3) pion condensation occurs at densities above normal nuclear matter density and leads to an equation of state with no stable density isomer.

The splitting of the isospin and spin-isospin dipole resonances in 12C

The splitting of the spin-isospin dipole resonance, which has been observed in the recent measurements of the cross section for electro-excitation of 12C, is discussed together with the splitting of the isospin dipole resonance on the basis of the deformed nuclear model. The obtained distribution of the isospin and spin-isospin excitation strength over the giant resonance region is in good agreement with experiment. In particular, it is found that the strong spin-isospin transition should appear in the same energy region (≈ 23 MeV) as that of the isospin mode. This result provides a reasonable fit with the cross section for electron scattering from 12C observed at backward angles with high-momentum transfer which could not be explained by previous studies.