Low- and intermediate-energy nucleon-nucleon interactions and the analysis of deuteron photodisintegration within the dispersion relation technique

The nucleon-nucleon interaction in the region of the nucleon kinetic energy up to 1000 MeV is analysed together with the reaction $\gamma d \to pn$ in the photon energy range $E_{\gamma}=0-400$ MeV. Nine nucleon-nucleon $s$-channel partial amplitudes are reconstructed in the dispersion relation $N/D$ method: $^1S_0$, $^3S_1-^3D_1$, $^3P_0$, $^1P_1$, $^3P_1$, $^3P_2$, $^1D_2$, $^3D_2$ and $^3F_3$. Correspondingly, the dispersive representation of partial amplitudes $N\Delta \to pn$, $NN^* \to pn$ and $NN\pi \to pn$ is given. Basing on that, we have performed parameter-free calculation of the amplitude $\gamma d \to pn$, taking into account: $(i)$ pole diagram, $(ii)$ nucleon-nucleon final-state rescattering $\gamma d \to pn \to pn$, and $(iii)$ inelastic final-state rescatterings $\gamma d \to N\Delta(1232) \to pn$, $\gamma d \to NN^*(1400) \to pn$ and $\gamma d \to NN\pi \to pn$. The $\gamma d \to pn$ partial amplitudes for nine above-mentioned channels are found. It is shown that the process $\gamma d \to pn \to pn$ is significant for the waves $^1S_0$, $^3P_0$, $^3P_1$, at $E_{\gamma} =50 -100$ MeV, while $\gamma d \to N\Delta \to pn$ for the waves $^3P_2$, $^1D_2$,$^3F_3$ dominates at $E_{\gamma} > 300$ MeV. Meson exchange current contributions into the deuteron disintegration are estimated: they are significant at $E_\gamma =100-400$ MeV.Comment: 22 pages, LaTeX, epsfig.sty, tabl

Self-consistent treatment of the quark condensate and hadrons in nuclear matter

We calculate the contribution of pions to the $\bar qq$-expectation value $\kappa(\rho)=$ in symmetric nuclear matter. We employ exact pion propagator renormalized by nucleon-hole and isobar-hole excitations. Conventional straightforward calculation leads to the "pion condensation" at unrealistically small values of densities, causing even earlier restoration of chiral symmetry. This requires a self-consistent approach, consisting in using the models, which include direct dependence of in-medium mass values on $\kappa(\rho)$, e.g. the Nambu-Jona-Lasinio-model. We show, that in the self-consistent approach the $\rho$-dependence of the condensate is described by a smooth curve. The "pion condensate " point is removed to much higher values of density. The chiral restoration does not take place at least while $\rho<2.8\rho_0$ with $\rho_0$ being the saturation value. Validity of our approach is limited by possible accumulation of heavier baryons (delta isobars) in the ground state of nuclear matter. For the value of effective nucleon mass at the saturation density we found $m^*(\rho_0)=0.6m$, consistent with nowadays results of other authors.Comment: 26 pages, LaTeX, 9 PostScript figures, epsfig.sty; sent to the European Physical Journal

Solutions of the dispersion equation in the region of overlapping of zero-sound and particle-hole modes

In this paper the solutions of the zero-sound dispersion equation in the random phase approximation (RPA) are considered. The calculation of the damped zero-sound modes \omega_s(k) (complex frequency of excitation) in the nuclear matter is presented. The method is based on the analytical structure of the polarization operators \Pi(\omega,k). The solutions of two dispersion equations with \Pi(\omega,k) and with Re(\Pi(\omega,k)) are compared. It is shown that in the first case we obtain one-valued smooth solutions without "thumb-like" forms. Considering the giant resonances in the nuclei as zero-sound excitations we compare the experimental energy and escape width of the giant dipole resonance (GDR) in the nucleus A with \omega_s(k) taken at a definite wave vector k=k_A.Comment: 14 pages, 5 figures; revised versio