Differential and total breakup cross sections as well as vector and tensor analyzing powers for $p-d$ scattering are studied for energies above the deuteron breakup threshold up to $E_{\mathrm{lab}}=28\mathrm{}\hspace{0.5em}\mathrm{MeV}.$ The $p-d$ scattering wave function is expanded in terms of the correlated hyperspherical harmonic basis and the elastic S matrix is obtained using the Kohn variational principle in its complex form. The effects of the Coulomb interaction, which are expected to be important in this energy range, have been rigorously taken into account. The Argonne AV18 interaction and the Urbana URIX three-nucleon potential have been used to perform a comparison to the available experimental data.

Isoscalar monopole and dipole compressional modes are computed for a variety of closed-shell nuclei in a relativistic random-phase approximation to three different parametrizations of the Walecka model with scalar self-interactions. Particular emphasis is placed on the role of self-consistency which by itself, and with little else, guarantees the decoupling of the spurious isoscalar-dipole strength from the physical response and the conservation of the vector current. A powerful new relation is introduced to quantify the violation of the vector current in terms of various ground-state form factors. For the isoscalar-dipole mode two distinct regions are clearly identified: (i) a high-energy component that is sensitive to the size of the nucleus and scales with the compressibility of the model and (ii) a low-energy component that is insensitivity to the nuclear compressibility. A fairly good description of both compressional modes is obtained by using a “soft” parametrization having a compression modulus of $K=224\mathrm{}\mathrm{MeV}.$

A stochastic transport description for the single-particle density matrix is briefly discussed. It is shown that the stochastic description contains, in addition to incoherent binary collisions, a coherent damping mechanism due to coupling between mean-field fluctuations and single-particle motion, and an expression for the coherent collision term is derived. In the limit of small fluctuations around equilibrium, the collective and single-particle self-energies due to the coherent mechanism are deduced.

The ground state properties of ${}^{90}\mathrm{Zr},$ ${}^{100}\mathrm{Sn},$ and ${}^{132}\mathrm{Sn}$ at equilibrium and at large amplitude compression are investigated. We use a realistic effective baryon-baryon Hamiltonian that includes $N-N,$ $N-\Delta ,$ and $\Delta -\Delta$ interactions. We perform the calculations in no-core model spaces within the framework of the constrained spherical Hartree-Fock approximation. We specifically investigate the sensitivity to the sizes of the nucleon and $\Delta$ model spaces. At equilibrium, we find no case of mixing between nucleons and $\Delta ’\mathrm{s}$ in our largest model space of eight major nucleon shells plus 16 $\Delta$ orbitals. On the contrary, there is mixing in ${}^{90}\mathrm{Zr},$ and ${}^{132}\mathrm{Sn}$ in the smaller model space of seven major nucleon shells plus eight $\Delta$ orbitals. Expanding the nucleon model space has a larger effect on reducing the static compression modulus and softening the nuclear equation of state than increasing the number of $\Delta$ states. Most of the excitation energy delivered to the system during compression is employed by two nuclei with a neutron excess (i.e., ${}^{90}\mathrm{Zr},$ ${}^{132}\mathrm{Sn})$ to create massive $\Delta$ resonances. On the other hand, in the ${}^{100}\mathrm{Sn}$ nucleus most of the excitation energy goes to a simple reduction in the binding, suggesting a suppressed role for the $\Delta$ states. Under extreme compression, at a density 2–3 times the normal nuclear density, the excitation of nucleons to $\Delta ’\mathrm{s}$ increases sharply up to 10% of the total number of constituents. At fixed excitation energy under compression, the number of $\Delta$ excitations is not dependent on the number of $\Delta$ states over the range studied. The $\Delta$-excitation results are consistent with heavy-ion collision data, and suggest an important mean field mechanism for subthreshold pion production in particle-nucleus and nucleus-nucleus collisions.

Present precision measurements of the neutron lifetime lead to a CKM matrix element $|V_{\mathrm{ud}}|,$ which is 3 standard deviations off the value inferred from heavy quark decays, etc. We investigate the possibility whether isospin-breaking effects in the neutron-to-proton vector current transition matrix element $〈p|V_0^{+}|n〉=1+\delta g_V$ could eventually close this gap. For that we calculate in chiral perturbation theory the effect of pion and kaon loops on the matrix element $〈p|V_0^{+}|n〉$ taking into account the mass differences of the charged and neutral mesons. We find a negligibly small isospin-breaking effect of $\delta g_V\simeq -4\times {10}^{-5}.$ The crucial quantity in the analysis of neutron $\beta$-decay precision measurements is thus the radiative correction term ${\Delta }_R.$ Furthermore, we calculate in heavy baryon chiral perturbation theory the SU(3) breaking effects on the vector transition charges of weak semileptonic hyperon decays. We find for these quantities channel-dependent relative deviations from the SU(3) limit which range from -10% to +1%.

The superfluidity of neutron matter in the channel ${}^1{S}_0$ is studied by taking into account the effect of the ground-state correlations in the self-energy. To this purpose the gap equation has been solved within the generalized Gorkov approach. A sizable suppression of the energy gap is driven by the quasiparticle strength around the Fermi surface.

In neutron-deuteron scattering, four total cross sections are shown to form a complete set for the determination of the imaginary parts of the forward amplitudes by means of the optical theorem. The amplitudes are decomposed into scalar and tensor components in spin space. Contributions of three-nucleon forces (3NF) to these amplitudes are studied by Faddeev calculations. Significant effects of the 3NF on the tensor components are predicted.

Collective $E2\mathrm{}$ transitions of midshell Ba isotopes are studied by means of the boson expansion theory. The fermion Hamiltonian is comprised of the self-consistent $\mathrm{QQ}$ interaction with higher-order (many-body) terms, monopole- and quadrupole-pairing interactions in addition to the spherical limit of the Nilsson Hamiltonian. The Kishimoto-Tamura method of normal-ordered linked-cluster expansion of the modified Marumori boson mapping is applied to construct the microscopic boson image of the Hamiltonian and that of the $E2\mathrm{}$ operator. It is shown that the marked increase of quadrupole collectivity, indicated by the enhancement of experimental $B\left(E2\mathrm{}\right),$ as neutron numbers approach the midshell value of $N=66\mathrm{}$ can be reproduced naturally in terms of the microscopic boson expansion theory by using a standard value of the effective charge.

The nucleus ${}_{30}^{65}\mathrm{Zn}$ was studied using the ${}^{52}\mathrm{Cr}{(}^{16}\mathrm{O},{2pn)}^{65}\mathrm{Zn}$ reaction at a beam energy of 65 MeV. A rotational band built on the $g_{9/2}$ neutron orbital was observed to exhibit a band crossing at a rotational frequency of 0.6 MeV with an associated alignment of $7ħ.$ This alignment is interpreted as being due to a pair of $g_{9/2}$ protons. Total Routhian Surface calculations have been carried out which confirm that the shape of the nucleus changes from an oblate shape at low spin to a triaxial prolate shape at intermediate spin.

We calculate the Coulomb displacement energies (CDEs) of mirror nuclei using the recent parameter set (NL3) in the relativistic mean-field (RMF) model which includes self-coupling of the scalar meson. The results obtained are compared with the available ones calculated in the nonrelativistic Skyrme-Hartree-Fock (SHF) approach that have the best fit to the experimental data. When adjusted to reproduce the charge root-mean-square (rms) radius $r_c$ and the rms radii of the valence orbits, the results of the RMF model for the CDEs agree with those of the SHF model within $\sim 1\%.$ Our investigation also shows that, although the RMF with the NL3 parameter set reproduces the kink in the isotope variation of $r_c,$ the values obtained for CDEs are too small to account for the experimental values without the addition of the contribution due to long-range correlation effects.

A representation of the fusion barrier distributions has been deduced from the back angle quasielastic scattering cross section data in ${}^{16,18}\mathrm{O}{+}^{12,124}\mathrm{Sn}$ reactions, measured over a wide range of bombarding energies around the Coulomb barrier. The results have been compared with coupled channel calculations using the CCDEF code to study the effects of projectile and target inelastic excitations and nucleon transfer couplings on the representation of fusion barrier distributions in these systems. The present studies bring out the importance of coupling of $2n$ pickup in the ${}^{16}\mathrm{O}{+}^{120,124}\mathrm{Sn}$ reactions and $2n$ stripping in the ${}^{18}\mathrm{O}{+}^{120,124}\mathrm{Sn}$ reactions in explaining the observed barrier distributions.

We calculate the shadowing effect in nuclear photoabsorption at low photon energies (1–3 GeV) within a multiple scattering approach. We avoid some of the high energy approximations that are usually made in simple Glauber theory like the narrow width and the eikonal approximation. We find that the main contribution to nuclear shadowing at low energies stems from ${\rho }^0$ mesons with masses well below their pole mass. We also show that the possibility of scattering in nonforward directions allows for a new contribution to shadowing at low energies: the production of neutral pions as intermediate hadronic states enhances the shadowing effect in the onset region. For light nuclei and small photon energies they give rise to about 30% of the total shadowing effect.

The proton-rich nuclei ${}^{23}\mathrm{Al}$ and ${}^{27}\mathrm{P}$ were studied using the ${}^{24}\mathrm{Mg}{(}^7\mathrm{Li}{,}^8\mathrm{He}{)}^{23}\mathrm{Al}$ and ${}^{28}\mathrm{Si}{(}^7\mathrm{Li}{,}^8\mathrm{He}{)}^{27}\mathrm{P}$ reactions, respectively. Several energy levels are observed in each nucleus. The mass excess of ${}^{23}\mathrm{Al}$ was measured to be 6.773(28) MeV and the mass excess of ${}^{27}\mathrm{P}$ was measured to be $-0.670\left(41\right)\mathrm{}\hspace{0.5em}\mathrm{MeV}.$ The first excited state of ${}^{23}\mathrm{Al}$ has been resolved from the ground state for the first time at an excitation energy of $E_x=0.550\mathrm{}\left(20\right)\mathrm{}\hspace{0.5em}\mathrm{MeV}.$ The first excited state of ${}^{27}\mathrm{P}$ has been measured for the first time at an excitation energy of $E_x=1.199\mathrm{}\left(19\right)\mathrm{}\hspace{0.5em}\mathrm{MeV}.$ The astrophysical implications of these results for the reaction rates of ${}^{22}\mathrm{Mg}(p,\gamma {)}^{23}\mathrm{Al}$ and ${}^{26}\mathrm{Si}(p,\gamma {)}^{27}\mathrm{P}$ for the nucleosynthesis of ${}^{22}\mathrm{Na}$ and ${}^{26}\mathrm{Al}$ in Ne novae will be discussed.

We calculated in detail the angular distribution of γ rays and the resulting shape of the γ-ray line produced by the nuclear deexcitation of the 4.439 MeV state of ${}^{12}\mathrm{C}$ following proton and α-particle interactions with ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ in the energy range from threshold to 100 MeV per nucleon, making use of available experimental data. In the proton energy range from 8.6 to 20 MeV, the extensive data set of a recent accelerator experiment on γ-ray line shapes and angular distributions was used to deduce parametrizations for the γ-ray emission of the $2^{+},$ 4.439 MeV state of ${}^{12}\mathrm{C}$ following inelastic proton scattering off ${}^{12}\mathrm{C}$ and proton induced spallation of ${}^{16}\mathrm{O}.$ At higher proton energies and for α-particle induced reactions, optical model calculations were the main source to obtain the needed reaction parameters for the calculation of γ-ray line shapes and angular distributions. Line shapes are predicted for various interaction scenarios of accelerated protons and α particles in solar flares.

The root-mean-square radii for neutrons in nuclei and their relationship to the neutron equation of state are investigated in the relativistic Hartree model. A correlation between the neutron skin in heavy nuclei and the derivative of the neutron equation of state is found which provides a linear continuation of results obtained from nonrelativistic Hartree-Fock models. The relativistic models tend to give larger neutron radii and an associated stiffer neutron equation of state compared with the nonrelativistic models.

A model for the pionic components of nuclear wave functions is obtained from light front dynamical calculations of binding energies and densities. The pionic effects are small enough to be consistent with measured nuclear dimuon production data and with the nucleon sea. But the pion effects are large enough to predict substantial nuclear enhancement of the cross section for longitudinally polarized virtual photons for the kinematics accessible at Jefferson Laboratory.

The $\alpha$-particle width of the 6.917 MeV, $J^{\pi }{=2\mathrm{}}^{+}$ state in ${}^{16}\mathrm{O}$ is the most uncertain value in the determination of the $E2\mathrm{}$ radiative ground state transition of the astrophysically important ${}^{12}\mathrm{C}(\alpha ,\gamma {)}^{16}\mathrm{O}$ reaction at energies relevant to stellar helium burning. As discussed previously in literature it is possible in principle to derive a precise value of the $\alpha$ width of the 6.917 MeV state by measuring the $E2\mathrm{}$ direct capture into this state. Here the theory based on the R-matrix formalism connecting the cascade direct capture and the $E2\mathrm{}$ ground state transition is described in more complete form than hitherto and resulting direct capture cross sections are estimated. In addition, conditional fits are made to existing data and the resulting value of the $\alpha$-particle width is discussed. From these considerations the cascade cross sections are found to be of the order of 10 nb in an extended energy range proposed to be measured. Angular distributions for the primary $\gamma$ transition are also given. Conclusions for future experiments are then drawn. The branching ratio of the $7.\overrightarrow{1}6.9\mathrm{MeV}\gamma$ transition should also be measured.

A fully microscopic interpretation of the phonon damping model (PDM) is proposed. The phonon operator, which generates the collective excitation such as giant dipole resonance (GDR), is constructed from coherent particle-hole pairs. The phonon energy is determined as the solution of dispersion equation within the random-phase approximation (RPA). The phonon structure is found in term of RPA X and Y amplitudes. The formalism is illustrated by numerical calculations within a schematic model. The results of calculations demonstrate the same feature of GDR as a function of temperature obtained previously within PDM-1, which employs structureless phonons.

We study, using molecular dynamics techniques, how boundary conditions affect the process of fragmentation of finite, highly excited, Lennard-Jones systems. We analyze the behavior of the caloric curves (CC), the associated thermal response functions (TRF), and cluster mass distributions for constrained and unconstrained hot drops. It is shown that the resulting CC for the constrained case differ from the one in the unconstrained case, mainly in the presence of a “vapor branch.” This branch is absent in the free expanding case even at high energies. This effect is traced to the role played by the collective expansion motion. On the other hand, we found that the recently proposed characteristic features of a first order phase transition taking place in a finite isolated system, i.e., abnormally large kinetic energy fluctuations and a negative branch in the TRF, are present for the constrained (dilute) as well as the unconstrained case. The microscopic origin of this behavior is also analyzed.

Uncertainty of the hyperon couplings, in particular, that of the ${\Sigma }^{-},$ in dense matter raises the question of the behavior of the electrochemical potential in neutron star matter, which is crucial to the possible presence of the kaon condensed phase. We show that regardless of this uncertainty, the $\Lambda$ hyperon, whose coupling can be constrained by its binding in nuclear matter and other observations, by itself, or also aided by the ${\Xi }^{-},$ introduces a saturation of the electrochemical potential just as the ${\Sigma }^{-}$ would otherwise do, which tends to mitigate against kaon condensation. The maximum possible mass of neutron stars appears to be $\sim (1.5\mathrm{}–{1.7)M}_{\odot }$ independent of the uncertainties, the limit being imposed by any one of hyperonization, deconfinement, or kaon condensation. Interestingly, such a limit is barely higher than the Chandrasekhar limit on the iron core mass of presupernova stars. This leaves a very small mass window for the existence of neutron stars, for the occurrence of supernovas, and therefore for a universe containing heavy elements and at least one planet with life.