The usefulness of the quon expansion to treat Pauli principle violations and many-body correlations in many-fermion systems is investigated within two models, namely, the Lipkin and the two level pairing models. The q deformation parameter of the quon algebra is fixed through a dynamical criterion. The spectra obtained are compared with the random-phase approximation (RPA), usual boson expansion, and exact results. The quonic expansion is shown to take into account correlations which are not included either in the second order boson expansion or in the RPA approach.

Various global characteristics of the coupling between bound and scattering states are explicitly studied on the basis of the realistic shell model embedded in the continuum. The characteristics are related to those of the scattering ensemble. It is found that in the region of high level density, the coupling matrix elements to the continuum are consistent with the assumptions of the statistical model. However, the assumption of channel equivalence is, in general, violated and the real part of the coupling matrix elements cannot be neglected.

Properties of nuclear matter are calculated in the Dirac-Hartree-Fock approximation within the Zimányi and Moszkowski model, which considers a derivative coupling in the scalar field. The present model improves the previous $\sigma -\omega$ version, by the inclusion of the charged mesons $\pi$ and $\rho .$ The $\pi N$ interaction is a mixing of pseudoscalar and pseudovector couplings. The introduction of the $\pi$ degrees of freedom has a strong influence on the nucleon effective mass, while keeping the compression modulus in a range of values in agreement with experiments. Effects on the spin-orbit splitting are also discussed.

Medium modified effective two nucleon interactions have been defined for protons incident upon ${}^{12}\mathrm{C}$ with energies ranging from 40 to 800 MeV. Those effective interactions have been folded with ground state density matrices from a large space shell model of ${}^{12}\mathrm{C}$ to give complex nonlocal optical potentials. With those the elastic scattering differential cross sections and analyzing powers have been analyzed. Good results are obtained when the effective interactions are linked to $\mathrm{NN}$ interactions that fit $\mathrm{NN}$ scattering data and when exchange amplitudes in scattering that lead to strong nonlocality in the optical potentials are taken into account.

We have studied the isotope dependence of deeply bound pionic states in Sn and Pb in order to examine the possibility of obtaining important information on neutron density distribution and the modification of the pion decay constant $f_{\pi }$ in a nuclear medium. Formation cross sections of the pionic states are calculated in the ${(d,}^3\mathrm{He})$ reactions. The present results indicate that the isotope dependence of the pionic states can be deduced from the experimental data with accessible energy resolution. The effects of the neutron skin for the formation cross sections are also examined and are found to affect the ${(d,}^3\mathrm{He})$ spectra significantly.

Fission and evaporation residue cross sections, and fission fragment anisotropies, for the reaction ${}^{34}\mathrm{S}{+}^{168}\mathrm{Er}$ have been measured to energies where the fission barrier no longer controls the fission process. Anisotropies calculated with the transition state model were found to be in excess of the measured anisotropies. Such an effect can be explained by assuming that the high angular momentum trajectories that lead to fission have some memory of the broad entrance-channel K distribution.

Total reaction cross sections ${\sigma }_R$ of $(30\mathrm{}–60)A\mathrm{MeV}$ ${}^{4,6,8}\mathrm{He}$ and ${}^{6,7,8,9,11}\mathrm{Li}$ on Pb, and $2n$-removal cross sections ${\sigma }_{-2n}$ of ${}^{6,8}\mathrm{He}$ and ${}^{11}\mathrm{Li}$ on Pb, were measured by injecting magnetically separated, focused, monoenergetic, secondary beams of those projectiles into a telescope containing Pb targets separated by thin Si detectors. All these ${\sigma }_R$’s (except ${}^4\mathrm{He}),$ and ${\sigma }_{-2n}$ for ${}^6\mathrm{He}$ and ${}^{11}\mathrm{Li},$ are underpredicted by microscopic model calculations which include only nuclear forces. Better agreement is achieved by including electromagnetic dissociation in the model, for those projectiles for which either the electric dipole response functions or the dominant photodissociation cross sections were known. The cross sections ${\sigma }_{-4n}$ for ${}^8\mathrm{He},$ ${\sigma }_{-\mathrm{xn}}$ for ${}^{7,8,9}\mathrm{Li},$ and $({\sigma }_{-3n}+{\sigma }_{-4n})$ for ${}^{11}\mathrm{Li}$ were found to be ⩽0.7 b. All ${\sigma }_R$’s were measured to better than 5% accuracy, showing that the method is usable for other target elements sandwiched into a Si telescope.

Multipion production in high energy nucleus-nucleus collisions is considered within the model of the pion radiation by classical current. Strong coherent effects of narrowing of the pion longitudinal and transverse momentum distributions are predicted at RHIC energies. The coherence enhances the large pseudorapidities, producing a bump in the distribution. The growth of the average pion multiplicity and oscillation effect in the multiplicity distribution are caused by the coherence as well.

We present a model for dressing the nucleon propagator and vertices. In the model the use of a K-matrix approach (unitarity) and dispersion relations (analyticity) are combined. The principal application of the model lies in pion-nucleon scattering where we discuss effects of the dressing on the phase shifts.

It is shown that the “folding model” approximation to Glauber’s theory of the high-energy scattering of composites of strongly absorbed particles always overestimates the reaction cross section.

We calculate the order ${\alpha }_s$ finite temperature correction to dilepton production in quark-gluon plasma arising from the two-loop photon self-energy diagrams for high invariant mass $M\gg T.\mathrm{}$

We show that the collision term in extended temperature-dependent Hartree-Fock not only induces a damping of collective states but also leads to a coupling between random-phase approximation states. This coupling may reorganize the collective response and may induce a transition from zero to first sound. Applying this formalism to the monopole and dipole responses in the calcium nucleus, it is found that the coupling between collective states through their decay channel remains small up to several MeV temperature. Therefore, the computed effect appears not to be strong enough to bring the considered nucleus in the first sound regime.

We discuss medium modifications of the unitarized pion-pion interaction in the nuclear medium. We incorporate both the effects of chiral symmetry restoration and the influence of collective nuclear pionic modes originating from the p-wave coupling of the pion to delta-hole configurations. We show in particular that the dropping of the sigma-meson mass significantly enhances the low-energy structure created by the in-medium collective pionic modes.

Bose-Einstein correlations of two identically charged pions are derived when these particles, the most abundantly produced in relativistic heavy-ion collisions, are confined in finite volumes. Boundary effects on a single-pion spectrum are also studied. Numerical results emphasize that the conventional formulation usually adopted to describe two-pion interferometry should not be used when the source size is small, since this is the most sensitive case to boundary effects. Specific examples are considered for better illustration.

Three related features of the astrophysical S-factor, $S_{17},$ for low energies are an upturn as the energy of the proton goes to zero, a pole at the proton separation energy, and a long-ranged radial integral peaking at approximately 40 fm. These features, particularly the last, mean $S_{17}$ at threshold is largely determined by the asymptotic normalization of the proton bound-state wave function. In this paper we identify the pole contribution to the S-factor without any explicit consideration of the asymptotic behavior of the bound-state wave function. This allows us to calculate $S_{17}$ in terms of purely short-range integrals involving the two-body potential. Much of the discussion is relevant to other radiative capture processes with weakly bound final states.

Pion-nucleus scattering has been analyzed using an equivalent local potential to calculate the differential cross sections for pions elastically scattered from ${}^{12}\mathrm{C},{\hspace{0.5em}}^{16}\mathrm{O},{\hspace{0.5em}}^{28}\mathrm{Si},$ and ${}^{40,44,48}\mathrm{Ca}$ in the energy range of 30 to 292 MeV. The DWUCK4 computer program was used to predict observables of pion-nucleus elastic scattering. Our results are successfully compared to recent data. The skin neutrons in ${}^{44,48}\mathrm{Ca}$ contribute to ${\pi }^{\pm }$ elastic scattering in this energy range more than the protons.

The deeply bound pionic states ${\mathrm{}(1s,2p)\mathrm{}}_{{\pi }^{-}}{\otimes }^{207}\mathrm{Pb}$ were observed for the first time, by investigating the ${}^{208}\mathrm{Pb}{(d,}^3\mathrm{He})$ reaction at a beam energy of $T_d=604.3\mathrm{}\mathrm{MeV}$ and at ejectile angles around 0°. The measured momentum distribution of the ${}^3\mathrm{He}$ particles was used to determine the Q value spectrum in the region $-145\mathrm{MeV}<Q<\mathrm{}-120\mathrm{MeV}$ with a systematic uncertainty of ±120 keV and a full width at half maximum resolution of $480\pm 60\mathrm{keV}.$ This spectrum shows a prominent peak at $Q\simeq -135.5\mathrm{MeV},$ corresponding to the pionic $2p$ state, coupled mainly to the ${3p}_{1/2}$ and ${3p}_{3/2}$ neutron hole states in ${}^{207}\mathrm{Pb}.$ A shoulder is seen on the tail of this dominant peak, and is attributed to the population of the pionic $1s$ state. The cross section for the continuum component at these high excitation energies is $d^2\sigma /\left(d\Omega dE\right)=4.7\mathrm{}\mu \mathrm{b}/\mathrm{s}\mathrm{r}\mathrm{}\mathrm{MeV}.$ The net cross section for production of ${\pi }^{-}$ states in the bound pion region $-140\mathrm{MeV}<Q<\mathrm{}-133\mathrm{MeV}$ above the continuum amounts to $d\sigma /d\Omega =76\mathrm{}\mu \mathrm{b}/\mathrm{s}\mathrm{r}.$

We find a remarkable agreement of the excitation energy spectrum of the ${}^{208}\mathrm{Pb}{(d,}^3\mathrm{He})$ reaction measured at $T_d=600\mathrm{}\mathrm{MeV}$ near the ${\pi }^{-}$ production threshold with its theoretical prediction. Their comparison leads us to assign the distinct narrow peak observed at about 5 MeV below the threshold to the formation of bound pionic states ${\pi }^{-}{\otimes }^{207}\mathrm{Pb}$ of the quasisubstitutional configurations ${\mathrm{}\left(2p\right)\mathrm{}}_{{\pi }^{-}}{(3p}_{3/2}{,3p}_{1/2}{)}_n^{-1}.$ A small bump observed on the tail of the peak is assigned to the pionic $1s$ state. The binding energies ${(B}_{\mathrm{nl}})$ and the widths $\left({\Gamma }_{\mathrm{nl}}\right)$ of the pionic orbitals are deduced to be $B_{2p}=5.13\mathrm{}\pm 0.02\mathrm{}\left(\mathrm{stat}\right)\mathrm{}\pm 0.12\mathrm{}\left(\mathrm{syst}\right)\mathrm{}\mathrm{}\mathrm{MeV}$ and ${\Gamma }_{2p}=0.43\mathrm{}\pm 0.06\mathrm{}\left(\mathrm{stat}\right)\mathrm{}\pm 0.06\mathrm{}\left(\mathrm{syst}\right)\mathrm{}\mathrm{}\mathrm{MeV}$ by decomposing the experimental spectrum into the pionic $1s$ and $2p$ components. While $B_{2p}$ and ${\Gamma }_{2p}$ are determined with small ambiguity, $B_{1s}$ and ${\Gamma }_{1s}$ are strongly correlated with each other, and are affected by the relative $1s/2p$ cross section ratio assumed, since the $1s$ component is observed only as an unresolved bump. Thus, we have to allow large uncertainties $6.6\mathrm{MeV}<B_{1s}<6.9\mathrm{}\mathrm{MeV}$ and $0.4\mathrm{MeV}<{\Gamma }_{1s}<1.2\mathrm{}\mathrm{MeV}.$ The experimental binding energies and widths are compared with theoretically calculated values based on various optical potential parameter sets, and are jointly used to deduce the effective ${\pi }^{-}$ mass in the nuclear medium.

We calculate for the first time the surface tension and curvature coefficient of a first-order phase transition between two possible phases of cold nuclear matter, a normal nuclear matter phase in equilibrium with a kaon-condensed phase, at densities a few times the saturation density. We find the surface tension is proportional to the difference in energy density between the two phases squared. Furthermore, we show the consequences for the geometrical structures of the mixed-phase region in a neutron star.