We study a generalized ladder diagram resummation in the superfluid phase of nuclear matter. The approach is based on a conserving generalization of the usual T-matrix approximation including also anomalous self-energies and propagators. The approximation here discussed is a generalization of the usual mean-field BCS approach to superfluidity. The numerical results in this work are obtained in the quasiparticle approximation. Properties of the resulting self-energy, superfluid gap, and spectral functions are studied.

The boson-conserving one-nucleon transfer operator in the interacting boson model (IBM) is reanalyzed. Extra terms are added to the usual form used for that operator. These new terms change generalized seniority by one unit, as the ones considered up to now. The results obtained using the new form for the transfer operator are compared with those obtained with the traditional form in a simple case involving the pseudospin Bose-Fermi symmetry $U^B\mathrm{}\left(6\right)\mathrm{}\otimes U^F\mathrm{}\left(12\right)\mathrm{}$ in its $U^{\mathrm{BF}}\mathrm{}\left(5\right)\mathrm{}\otimes U^F\mathrm{}\left(2\right)\mathrm{}$ limit. Sizeable differences are found. These results are of relevance in the study of transfer reactions to check nuclear supersymmetry and in the description of $\beta$ decay within IBM.

The generalized hybrid derivative coupling model is applied to study the ground-state deformation and binding energy of even-even Ne, Mg, Si, and S isotopes. The energy surface is plotted as a function of the axial deformation.The deformation values predicted in the present calculation are closer to experimentally observed values in most nuclei in this region in comparison to other relativistic calculations. The ground state binding energy prediction, in contrast, is poorer. A number of nuclei, like ${}^{18,28}\mathrm{Ne},$ ${}^{20}\mathrm{Mg},$ ${}^{36}\mathrm{Si},$ and ${}^{38,54}\mathrm{S},$ may be triaxial in their ground state. The shape of the nuclei with $N=20\mathrm{}$ cannot be explained at the mean-field level and neutron excitation across the shell gap is expected to play a major role. The neutron number $N=8\mathrm{}$ may no longer be a magic number in the drip line nuclei in this region.

We measured the ${}^{17}\mathrm{O}(n,\alpha {)}^{14}\mathrm{C}$ reaction cross section from subthermal up to about 350 keV neutron energy. Two distinct resonances were observed at 178 and 253 keV, respectively, and a bump in our data near 2 keV could be explained by the presence of a negative-energy p-wave resonance. In the lower energy region, the cross section was shown to have a $1/v$ shape. The ${}^{17}\mathrm{O}(n,\alpha {)}^{14}\mathrm{C}$ reaction is of importance in two different applications: it is one of the major reactions responsible for the ${}^{14}\mathrm{C}$ pollution in nuclear reactors. Also, this reaction plays a role in primordial and nucleosynthesis in various astrophysical scenarios. For this application, the reaction rate at astrophysically relevant temperatures was calculated.

The double-differential cross sections and analyzing powers over an angular range of $30°<~{\theta }_{\mathrm{lab}}<~75°,$ and the induced polarizations P and polarization transfer values $D_{\mathrm{NN}}$ at $30°$ and $40°$ for the ${}^{40}\mathrm{Ca}\mathrm{}(p,n)\mathrm{}$ reaction are measured at a bombarding energy of 345 MeV. The data are compared with theoretical calculations in a semiclassical distorted wave (SCDW) model employing through three- and two-step contributions for cross sections and polarization observables, respectively. At forward angles, the SCDW calculations reproduce the observed cross sections fairly well around the quasielastic peak. The one-step contribution is dominant at ${\theta }_{\mathrm{lab}}=30\mathrm{}°,$ while the two- and three-step contributions become more important with increasing reaction angle. At backward angles the calculations underestimate the cross sections in the whole region, which indicates the significance of higher-step contributions. The $D_{\mathrm{NN}}$ values, which are sensitive to the effective nucleon-nucleon interaction in the nuclear medium, are close to those calculated with the G-matrix interaction parametrized by the Melbourne group.

A spherical optical model potential (OMP) containing a dispersive term is used to fit the available experimental database of $\sigma \left(\theta \right)$ and ${\sigma }_T$ for ${n+}^{27}\mathrm{Al}$ covering the energy range 0.1–250 MeV using relativistic kinematics and a relativistic extension of the Schrödinger equation. A dispersive OMP with parameters that show a smooth energy dependence and an energy-independent geometry are determined from fits to the entire data set. A very good overall agreement between experimental data and predictions is achieved up to 150 MeV. Inclusion of nonlocality effects in the absorptive volume potential allows one to achieve an excellent agreement up to 250 MeV.

The nonmesonic decay rates and the lifetimes of hypernuclei of mass $A=4\mathrm{}-209$ are extensively calculated based on the $1\pi ,$ correlated-$2\pi ,$ and $1\omega$ exchange potentials. Two types of new hyperon-nucleon potentials have been constructed in which the two pions are correlated and coupled to ρ and/or σ in the exchange process. The roles of these potentials and $1\omega$ exchange potential are discussed. The theoretical decay rates are consistent with the existing data for s-shell and p-shell hypernuclei within the present model. The calculated decay rate increases gradually up to $A\simeq 60$ and then tends to be almost constant for $A\gtrsim 60.$ The A-dependent behavior of the hypernuclear lifetimes tends to be constant over the mass region $A>\mathrm{}30\mathrm{}$ of hypernuclei in our model. It is most remarkable that the cooperative effect of the correlated-$2\pi$ and $1\omega$ exchanges enhances the neutron-stimulated decay rate ${\Gamma }_n$ (proton-stimulated one ${\Gamma }_p)$ by 400–450 % (20–30 %) with respect to the standard $1\pi$-exchange estimate for $A>\mathrm{}5.\mathrm{}$ As a result the ${\Gamma }_n/{\Gamma }_p$ ratios for light-to-heavy hypernuclei are calculated to be 0.4–0.5, which values are several times larger than the $1\pi$-exchange estimate. Although the experimental ratios seem still about two times larger than these theoretical values, it has revealed that the representative $2\pi$-exchange and $1\omega$ exchange mechanisms give rise to a clear improvement on the ${\Gamma }_n/{\Gamma }_p$ ratios.

Data from a number of different experimental measurements are used to construct caloric curves for five different regions of nuclear mass. These curves are qualitatively similar, and exhibit plateaus at the higher excitation energies. The limiting temperatures represented by the plateaus decrease with increasing nuclear mass, and are in very good agreement with results of recent calculations employing either a chiral symmetry model or the Gogny interaction. This agreement strongly favors a soft equation of state. Evidence is presented which suggests that critical excitation energies and critical temperatures might be determined from caloric curve measurements when the mass variations inherent in such measurements are taken into account.

We address the role of fluctuations in strongly interacting matter during the dense stages of a heavy-ion collision through its electromagnetic emission. Fluctuations of isospin charge are considered in a thermal system at rest as well as in a moving hadronic fluid at fixed proper time within a finite bin of pseudorapidity. In the former case, we use general thermodynamic relations to establish a connection between fluctuations and the spacelike screening limit of the retarded photon self-energy, which directly relates to the emissivities of dileptons and photons. Effects of hadronic interactions are highlighted through two illustrative calculations. In the latter case, we show that a finite time scale $\tau$ inherent in the evolution of a heavy-ion collision implies that equilibrium fluctuations involve both spacelike and timelike components of the photon self-energy in the system. Our study of nonthermal effects, explored here through a stochastic treatment, shows that an early and large fluctuation in isospin survives only if it is accompanied by a large temperature fluctuation at freeze-out, an unlikely scenario in hadronic phases with large heat capacity. We point out prospects for the future which include (1) a determination of the Debye mass of the system at the dilute freeze-out stage of a heavy-ion collision and (2) a delineation of the role of charge fluctuations during the dense stages of the collision through a study of electromagnetic emissivities.

We have measured the production of light nuclei $(A<~3)$ in $11.6\hspace{0.5em}\mathrm{GeV}/c$ Au-Au collisions at the Brookhaven Alternating Gradient Synchrotron (AGS). The transverse mass spectra are analyzed using a thermal fireball model, and the yields for different particle species are discussed assuming coalescence and fragmentation as possible production mechanisms. The wide acceptance range of the ${}^3\mathrm{He}$ measurements permits a broad study of the coalescence parameter $B_3$ as functions of transverse momentum and rapidity. Comparisons with data obtained previously at AGS energies suggest that the simple models are insufficient to describe fully the production mechanisms of light nuclei.

Within first-order phase transitions, we investigate pretransitional effects due to the nonperturbative, large-amplitude thermal fluctuations which can promote phase mixing before the critical temperature is reached from above. In contrast with the cosmological quark-hadron transition, we find that the rapid cooling typical of the relativistic heavy ion collider and large hadron collider experiments and the fact that the quark-gluon plasma is chemically unsaturated suppress the role of nonperturbative effects at current collider energies. Significant supercooling is possible in a (nearly) homogeneous state of quark gluon plasma.

The production of ${\Delta }^0$ and ${\Delta }^{++}$ resonances in high energy collisions of carbon nuclei with the carbon nucleus, using a 2-m propane bubble chamber, was investigated. From invariant masses of $(p,{\pi }^{\pm })$ pairs the masses and widths of the resonances were obtained. The ratios of pion production from delta decays and direct pion creation were estimated, as well as the relative number of nucleons excited to ${\Delta }^0$ at freeze-out conditions.

We investigate the electromagnetic form factors of nucleons within a simple relativistic quark spectator-diquark model using the light-cone formalism. Melosh rotations are applied to both quark and vector diquark. It is shown that the difference between vector and scalar spectator diquarks reproduces the right electric form factor of neutrons, and both the form factors $G_E{(Q}^2)$ and $G_M{(Q}^2)$ of the proton and neutron agree with experimental data well up to $Q^2=2\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^2$ in this simple model.

We study the electric and magnetic polarizability coefficients to subleading order in the inverse number of colors $N_c^{-1}$ by constructing Compton scattering amplitudes derived from a bosonized version of the Nambu– Jona-Lasinio (NJL) chiral Lagrangian with finite pion size effects included. We confirm the leading in $N_c^{-1}$ mean-field results of Bajc et al. [Nucl. Phys. $\mathbf{A}604\mathrm{},$ 406 (1996)] to $\mathcal{O}{(m}_{\pi }^2)$ in the pion mass $m_{\pi }.$ The subleading corrections arise from a gauge invariant sum of meson one-loop diagrams which is nonanalytic in $m_{\pi }^2,$ but free of any chiral or ultraviolet divergences. These corrections lead to a $\gtrsim 30\%$ reduction in the mean-field values for the polarizability coefficients of the charged pion. Use of the sum rule estimate for the NJL quark mass renders these calculations parameter free, and dependent only on the physical observables of the pion.

The proton-proton parity-violating longitudinal asymmetry is calculated in the laboratory-energy range 0–350 MeV, using a number of different, latest-generation strong-interaction potentials—Argonne $v_{18},$ Bonn-2000, and Nijmegen-I—in combination with a weak-interaction potential consisting of $\rho$- and $\omega$-meson exchanges—the model known as DDH. The complete scattering problem in the presence of parity conserving, including Coulomb, and parity-violating potentials is solved in both configuration and momentum space. The predicted parity-violating asymmetries are found to be only weakly dependent upon the input strong-interaction potential adopted in the calculation. Values for the $\rho$- and $\omega$-meson weak coupling constants $h_{\rho }^{\mathrm{pp}}$ and $h_{\omega }^{\mathrm{pp}}$ are determined by reproducing the measured asymmetries at 13.6 MeV, 45 MeV, and 221 MeV.

Parity violation in p-wave neutron resonances of the palladium isotopes 104, 105, 106, and 108 has been measured by transmission of a longitudinally polarized neutron beam through a natural palladium target. The measurements were performed at the pulsed spallation neutron source of Los Alamos Neutron Science Center. The rms weak interaction matrix elements and the corresponding spreading widths were determined for ${}^{104}\mathrm{Pd},$ ${}^{105}\mathrm{Pd},$ and ${}^{106}\mathrm{Pd}.$

Real photon scattering experiments have been performed on the $N=Z$ nucleus ${}^{32}\mathrm{S}$ to investigate energies and absolute strengths of dipole and electric quadrupole excitations up to a maximum energy of $E_x=9.9\mathrm{}\mathrm{MeV}.$ Evidence for a $2^{+}\otimes 3^{-}$ two-phonon state, which is well established in heavier nuclei, is discussed.

We examine a recently proposed nucleon-nucleon interaction, claimed by its authors both to be realistic and to lead to a standing-wave instability in symmetric nuclear matter. Contrary to these claims, we find that this interaction leads to a serious overbinding of ${}^4\mathrm{He},$ ${}^{16}\mathrm{O},$ and ${}^{40}\mathrm{Ca}$ nuclei when the Hartree-Fock method is properly applied. The resulting nuclear densities contradict the experimental data and all realistic Hartree-Fock results.

Excited states in the $T_z=\frac{1}{2}$ nucleus ${}^{85}\mathrm{Mo}$ have been observed for the first time with the reaction ${}^{58}\mathrm{Ni}{(}^{32}\mathrm{S},\alpha n\gamma )$ at 105 MeV. $\gamma$-ray transitions in this nucleus have been assigned unambiguously by combining the information from the GASP $\gamma$-ray array, the ISIS silicon ball, and the n-Ring neutron detector. Two band structures have been observed in this nucleus; they continue the smooth evolution of the known bands from the lighter $N=43\mathrm{}$ isotones and have been tentatively assigned spins and parity on this basis. After reaching a maximum of collectivity at ${}^{83}\mathrm{Zr},$ the trend with increasing mass is reversed, showing a smaller collectivity at ${}^{85}\mathrm{Mo}.$ The rotational behavior of the observed bands is discussed on the basis of the projected shell model calculations.

Triangle Feynman diagrams can be considered as describing form factors of states bound by a zero-range interaction. These form factors are calculated for scalar particles and compared to point-form and nonrelativistic results. By examining the expressions of the complete calculation in different frames, we obtain an effective boost transformation, which can be compared to the relativistic kinematical one underlying the present point-form calculations, as well as to the Galilean boost. The analytic expressions obtained in this simple model allow a qualitative check of certain results obtained in similar studies. In particular, a mismatch is pointed out between recent practical applications of the point-form approach and the one originally proposed by Dirac.