Consideration of Coulomb energies for ${}^{12}\mathrm{O}$ and ${}^{12}\mathrm{Be},$ combined with other information, strongly suggests that the ${}^{12}\mathrm{Be}$(g.s.) contains about 52% of the configuration ${}^{10}\mathrm{Be}(\mathrm{g}.\mathrm{s}.\mathrm{})\otimes (2s\frac{1}{2}{)}^2.$

The reaction $A(\pi ,\pi \pi )X$ has been studied at low energies, paying particular attention to the interaction of the two final pions in the scalar isoscalar $\mathrm{}(I=J=0\mathrm{})\mathrm{}$ channel. We have developed a microscopic model for the pion production, and then implemented the two pion final state interaction by using the results of a nonperturbative unitary coupled-channel method based in standard chiral Lagrangians. The resulting model describes well the reaction on the nucleon for all different isospin channels. Finally, we have considered the reaction in nuclei. Our calculation takes into account Fermi motion, Pauli blocking, pion absorption, and also the strong modification of the $\pi \pi$ interaction in the nuclear medium.

The first measurements of $f_{\mathrm{LT}}^{\prime },$ known as the fifth response function, have been made for the ${}^2\mathrm{H}\left(\overrightarrow{e}{,e}^{\prime }p\right)$ and ${}^{12}\mathrm{C}\left(\overrightarrow{e}{,e}^{\prime }p\right)$ reactions. This response is directly related to the imaginary part of the interference between the transverse and longitudinal nuclear electromagnetic currents. Its observation requires longitudinally polarized electron beams and out-of-plane detection, the latter made possible by the newly developed out-of-plane spectrometer system. The initial measurements were made by using a 560-MeV polarized electron beam and quasielastic kinematics at $Q^2=3.3\mathrm{}\hspace{0.5em}{\mathrm{fm}}^{-2}.$ The development of the methodology for out-of-plane physics, and the analysis of the data from the initial experiments are described in detail. The measured fifth response and the related asymmetry in the coincidence cross section are in agreement, albeit with large statistical errors, with the theoretical predictions. Future extensions of the out-of-plane program are also discussed.

The neutron-rich argon isotope ${}^{43}\mathrm{Ar}$ has been studied by quasielastic and inelastic proton scattering performed in inverse kinematics. The measured inelastic angular distribution for the second excited state is in good agreement with an $L=2\mathrm{}$ transition. Assuming this transition to be $E2,$ yields a ${\beta }_2$ value for this state of $0.25\pm 0.03$ when compared with distorted-wave Born approximation calculations. This value is comparable to the one reported for the stable isotope ${}^{40}\mathrm{Ar}.$ Moreover it is similar to those measured by Coulomb excitation for the neighboring even-even isotopes ${}^{42}\mathrm{Ar}$ and ${}^{44}\mathrm{Ar}$ indicating that the structure of the argon isotopes is stable as a function of neutron number.

We discuss the origin of the difference between the harmonic value of the width of the multiphonon giant resonances and the smaller observed value. Analytical expressions are derived for both the effective width and the average cross section. The contribution of the Brink-Axel mechanism in resolving the discrepancy is pointed out.

We deal with two different aspects of an exactly soluble statistical model of fragmentation. First we show, using zero range force and finite temperature Thomas-Fermi theory, that a common link can be found between finite temperature mean field theory and the statistical fragmentation model. We show the latter naturally arises in the spinodal region. Next we show that although the exact statistical model is a canonical model and uses temperature, microcanonical results which use constant energy rather than constant temperature can also be obtained from the canonical model using saddle-point approximation. The methodology is extremely simple to implement and at least in all the examples studied in this work is very accurate.

The expansion and hadronization of a quark meson plasma is studied using an effective chiral interaction Lagrangian. The particles we consider are light as well as strange quarks, which can form pions, kaons, and η mesons via collision processes. The transport equations for the system are solved using a QMD-type algorithm. We find that at vanishing baryon density at high temperatures the strange quark mass is considerably higher than the strange current quark mass and becomes even higher if we assume an initial state free of strange quarks. This leads to a considerably higher production threshold. In contrast to simpler scenarios, like the thermodynamics of free quarks with their bare mass, we observe that strangeness production in a baryon-free plasma is hindered and not favored. The different particle species created during the evolution become separated in coordinate as well as in momentum space. Thus the radial collective velocity, seen in the CERN experiments, may as well originate from a plasma expansion and not necessarily from a hadronic scenario.

We use a generalized Nambu–Jona-Lasinio (NJL) model to study pseudoscalar–axial-vector mixing for K mesons. As in a corresponding study of the pion, we find a series doublets in the confining field. When the short-range NJL interaction is included, one member of each doublet moves down in energy to a significant extent and has a small mixing angle. (Those states may be said to be “kaonlike,” while the other states may be called “mixed” states.) We find a mixing angle of -7.04° for the kaon and a kaon-quark coupling constant $g_{\mathrm{Kqq}}=\mathrm{8.09.}\mathrm{}$ With these values we find $f_K=115\mathrm{}\mathrm{MeV},$ which is quite close to the experimental value of $113.0\pm 1.3\mathrm{MeV}.$ (In the absence of pseudoscalar–axial-vector mixing, we have $g_{\mathrm{Kqq}}=5.77\mathrm{}$ and $f_K=85.7\mathrm{}\mathrm{MeV}.)$ The experimentally observed state $K\left(1460\right)\mathrm{}$ is a (nodeless) mixed state in our model and is calculated to be at 1369 MeV. (The value of the mass for this state is given in the data tables as being in the vicinity of 1400 or 1460 MeV, depending upon which of two experimental determinations one consid ers.) We find a total of six states with mass less than 2.0 GeV and provide mixing angles and coupling constants for these states.

The unitary quark model of Törnqvist and Roos provides an extremely interesting description of the properties of the scalar meson nonet. The model is quite phenomenological and has six parameters. In this work we are interested in seeing whether a theoretical foundation for the unitary quark model can be created using our generalized Nambu–Jona-Lasinio (NJL) model, which includes a covariant model of confinement. To make contact with Törnqvist’s work, it is necessary to go beyond the leading vacuum polarization diagram of the NJL model, ${J(P}^2),$ which is of order $n_c,$ and calculate the (complex) function ${K(P}^2),$ which is of order 1, and which describes the decay of $q\overline{q}$ states to the continuum of two-meson states. The central issue is the creation of a model for the regularization of the one-loop amplitudes with three vertices. We choose a regulator that has been used in our recent study of $f_0$ mesons. The same regularization is used for the πη, $K\overline{K},$ and $\pi {\eta }^{\prime }$ channels, when studying the properties of the $a_0\mathrm{}\left(980\right)\mathrm{}$ resonance. The coupling to the decay channels described by ${K(P}^2)$ is an important feature of the model, since the mass of the $a_0$ mass would be 1090 MeV in the absence of such coupling. The peak width obtained for the $a_0\mathrm{}\left(980\right)\mathrm{}$ resonance is 23 MeV, which is smaller than the values of 50–100 MeV usually quoted. (Larger values may be obtained in our calculation with another form of the regulator.) While our model is not parameter free, we believe we have made significant progress toward putting the unitary quark model on a firmer foundation.

A nonperturbative s-wave renormalization of the pion in a hot and baryon-rich medium is presented. This approach proceeds via a mapping of the canonical pion into the axial Noether’s charge. The mapping was made dynamical in the Hartree-Fock-Bogoliubov random-phase approximation. It is shown that this approach, while order mixing, is still symmetry conserving both in the baryon-free and baryon-rich sectors, at zero as well as finite temperature. The systematic character of this approach is emphasized and it is particularly argued that it may constitute an interesting alternative for the nonperturbative assessment of the nuclear matter saturation properties.

We discuss properties of quark matter at finite baryon densities and zero temperature in a Vlasov approach. We use a screened interquark Richardson’s potential consistent with the indications of lattice QCD calculations. We analyze the choices of the quark masses and the parameters entering the potential which reproduce the binding energy of infinite nuclear matter. There is a transition from nuclear to quark matter at densities five times above normal nuclear matter density. The transition could be revealed from the determination of the position of the shifted meson masses in dense baryonic matter. A scaling form of the meson masses in dense matter is given.

We calculate the spin polarizabilities of the nucleon by means of the dispersion relations applied to model-independent pion photoproduction amplitudes both in the $N\pi$ and $\Delta \pi$ channels. Here, we follow the idea of the ${1/N}_c$ expansion. By careful application of dispersion relations we show that the spin polarizabilities coincide with those in heavy baryon chiral perturbation theory, if we take the narrow decay-width limit of the $\Delta$ particle.

The problem of the near vanishing of the Gamow-Teller transition (GT) in the $A=14\mathrm{}$ system between the lowest ${J=0\mathrm{}}^{+}\hspace{0.5em}T=1\mathrm{}$ and ${J=1\mathrm{}}^{+}\hspace{0.5em}T=0\mathrm{}$ states is revisited. The model space is extended from the valence space ${(p}^{-2})$ to the valence space plus all $2ħ\omega$ excitations. The question is addressed as to what features of the effective nucleon-nucleon interaction in the medium are required to obtain the vanishing GT strength in this extended space. It turns out that a combination of a realistic strength of the tensor force combined with a spin-orbit interaction which is enhanced as compared to the free interaction yields a vanishing GT strength. Such an interaction can be derived from a microscopic meson exchange potential if the enhancement of the small component of the Dirac spinors for the nucleons is taken into account.

We report a significant improvement of an approximate method of including electron Coulomb distortion in electron-induced reactions at momentum transfers greater than the inverse of the size of the target nucleus. In particular, we have found a new parametrization for the elastic electron scattering phase shifts that works well at all electron energies greater than 300 MeV. As an illustration, we apply the improved approximation to the ${(e,e}^{\prime }p)$ reaction from medium and heavy nuclei. We use a relativistic “single-particle” model for ${(e,e}^{\prime }p)$ as as applied to ${}^{208}\mathrm{Pb}{(e,e}^{\prime }p)$ and to recently measured data at CEBAF on ${}^{16}\mathrm{O}{(e,e}^{\prime }p)$ to investigate Coulomb distortion effects.

The phenomenon of trapping of states is studied in the case of high-lying states with large angular momentum in the odd-$A$ nucleus ${}^{209}\mathrm{Pb}.$ The interaction of the single-particle mode with more complex states is calculated in the framework of the quasiparticle-phonon model while the coupling to the continuum is included by means of the projection operator method. The results obtained show a reduction of the spreading of the single-particle strength under the influence of the coupling to the continuum: the strength is concentrated on a few collective states while the remaining states are decoupled from the continuum (trapped). The results are compared with the case where continuum coupling is switched off. The influence of the continuum on the nuclear structure should be visible in nucleon transfer reactions.

We investigate the pion photoproduction off the nucleon in the $\Delta$ region in the framework of an effective chiral Lagrangian including pions, nucleon, and $\Delta \mathrm{}\left(1232\right).$ We work to third order in a small scale expansion with both $m_{\pi }$ and $M_{\Delta }-M_N$ treated as light scales. We note that in the $\Delta$ region, straightforward power counting breaks down as the amplitude becomes very large. To deal with this problem, we suggest that the appropriate way to compare the theoretical calculations with experimental data is via weighted integrals of the amplitudes through the $\Delta$ region.

A study of the ${}^{12}\mathrm{C}{(}^{16}\mathrm{O}{,}^{12}\mathrm{C}{(0\mathrm{}}_2^{+}){)}^{16}\mathrm{O}$ reaction over the energy interval $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=15\mathrm{}–34\hspace{0.5em}\mathrm{MeV}$ has been performed. A simple reaction model based on the strong absorption model with the coherent addition of a single partial wave has reproduced the main features of the excitation function. The model further suggests that two broad structures around 24 and 26.5 MeV arise from the low resolution observation of two or more overlapping peaks. With the possible exception of two $J=12\mathrm{}$ enhancements at 23.4 and 24.2 MeV, none of the structures have been definitively identified as resonances.

Three-pion interferometry is investigated for new information on the space-time structure of the pion source created in ultrarelativistic heavy-ion collisions. The two- and three-pion correlations are numerically computed for incoherent source functions based on the Bjorken hydrodynamical model, over a wide range of the kinematic variables. New information provided by three-pion interferometry, different from that provided by two-pion interferometry, should appear in the phases of the Fourier transform of the source function. Variables are identified that would be sensitive to the phases and suitable for observation. For a positive, chaotic source function, however, a variation of the three-pion phase is found to be difficult to extract from experiments. Effects of asymmetry of the source function are also examined.

We employ a bispinor gap equation to study superfluidity at nonzero chemical potential, $\mu \ne 0,$ in two- and three-color QCD, exploring the gap’s sensitivity to the nature of the quark-quark interaction. The two-color theory, ${\mathrm{QC}}_2\mathrm{D},$ is an excellent exemplar; the order of truncation of the quark-quark scattering kernel K has no qualitative impact, which allows a straightforward elucidation of the effects of $\mu$ when the coupling is strong. In the three-color theory the rainbow-ladder truncation admits diquark bound states, a defect that is eliminated by an improvement of K. The corrected gap equation describes a superfluid phase that is semiquantitatively similar to that obtained using the rainbow truncation. A model study suggests that the width of the superfluid gap and the transition point in ${\mathrm{QC}}_2\mathrm{D}$ provide reliable quantitative estimates of those quantities in QCD.

The $\beta$-delayed proton precursor ${}^{121}\mathrm{Ce}$ has been produced via the ${}^{92}\mathrm{Mo}{(}^{32}\mathrm{S},\mathrm{}3{n)}^{121}\mathrm{Ce}$ reaction and studied by using a He-jet tape transport system. The $\beta$-delayed proton spectrum populating the low-lying excited states in ${}^{120}\mathrm{Ba}$ was obtained, and the relative ratio of the proton branchs feeding the first and second excited states in ${}^{120}\mathrm{Ba}$ was measured to be 100:19. By using statistical model calculations the spin and parity for the ground state of ${}^{121}\mathrm{Ce}$ have been assigned to be ${5/2}^{+}$ or ${5/2}^{-}.$