Properties of the first excited state of the nucleus ${}^9$Be are discussed based on recent $(e,e^{\prime })$ and $(\gamma ,n$) experiments. The parameters of an $R$-matrix analysis of different data sets are consistent with a resonance rather than a virtual state predicted by some model calculations. The energy and the width of the resonance are deduced. Their values are rather similar for all data sets, and the energy proves to be negative. It is argued that the disagreement between the extracted $B\left(E1\right)$ values may stem from different ways of integration of the resonance. If corrected, fair agreement between the $(e,e^{\prime })$ and one of the $(\gamma ,n)$ data sets is found. A recent $(\gamma ,n)$ experiment at the HI$\gamma$S facility exhibits larger cross sections close to the neutron threshold which remain to be explained.

Cluster structures and monopole transitions in positive parity states of ${}^{16}\mathrm{O}$ are investigated based on the generator coordinate method calculation of an extended ${}^{12}\mathrm{C}$+$\alpha$ cluster model. The ground and excited states of a ${}^{12}\mathrm{C}$ cluster are taken into account by using ${}^{12}\mathrm{C}$ wave functions obtained with the method of antisymmetrized molecular dynamics. The $0_2^{+}$ state of ${}^{16}\mathrm{O}$ and its rotational members, the $2_1^{+}$ and $4_1^{+}$ states, are described well by the cluster states dominated by the ${}^{12}\mathrm{C}$($0_1^{+}$)+$\alpha$ structure. Above the ${}^{12}\mathrm{C}$($0_2^{+}$)+$\alpha$ threshold energy, I obtain a $0^{+}$ state having the ${}^{12}\mathrm{C}$($0_2^{+}$)+$\alpha$ cluster structure, which is considered to be a candidate for the $4\alpha$ cluster gas state. The band structures are discussed based on the calculated $E2$ transition strength. Isoscalar monopole excitations from the ground state are also discussed.

We report on a calculation of cross sections for charged-current quasielastic antineutrino scattering off ${}^{12}$C in the energy range of interest for the MiniBooNE experiment. We adopt the impulse approximation (IA) and use the nonrelativistic continuum random phase approximation (CRPA) to model the nuclear dynamics. An effective nucleon-nucleon interaction of the Skyrme type is used. We compare our results with the recent MiniBooNE antineutrino cross-section data and confront them with alternate calculations. The CRPA predictions reproduce the gross features of the shape of the measured double-differential cross sections. The CRPA cross sections are typically larger than those of other reported IA calculations but tend to underestimate the magnitude of the MiniBooNE data. We observe that an enhancement of the nucleon axial mass in CRPA calculations is an effective way of improving on the description of the shape and magnitude of the double-differential cross sections. The rescaling of $M_A$ is illustrated to affect the shape of the double-differential cross sections differently than multinucleon effects beyond the IA.

Shock waves constitute discontinuities in matter which are relevant in the study of plasma behavior in astrophysical scenarios and in heavy-ion collision. They can produce conical emission in relativistic collisions and are also thought to be the mechanism behind the acceleration of energetic particles in active galactic nuclei and $\gamma$-ray bursts. The shocks are mostly hydrodynamic shocks. In a magnetic background they become magnetohydrodynamic (MHD) shocks. For that reason we study the space-like and time-like shock discontinuity in a magnetic plasma. The shocks induce a phase transition in the plasma, here assuming a transition from hadron to quarks. The MHD conservation conditions are derived across the shock. The conservation conditions are solved for downstream velocities and flow angles for given upstream variables. The shock conditions are solved at different baryon densities. For the space-like shocks the anisotropy in the downstream velocity arises due to the magnetic field. The downstream velocity vector always points downward with respect to the shock normal. With the increase in density the anisotropy is somewhat reduced. The magnetic field has effectively no impact on time-like shocks. The slight anisotropy in the downstream flow velocities is caused by the boosting that brings the quantities from the fluid frame to a normal incidence frame.

The large number of high-spin bands that have been observed in $A=56–62$ nuclei are analyzed systematically within the cranked Nilsson-Strutinsky approach. Optimized Nilsson single-particle parameters are derived from investigations of energy differences between experimental and calculated rotational bands. Specifically, the relative energies of bands in neighboring nuclei whose configurations differ by having a high-$j$ orbital either filled or empty are analyzed. The level schemes calculated with the new Nilsson parameters are compared with those using standard Nilsson parameters. Some configuration assignments are revised.

In this work we investigate the coherent photoproduction of $\psi \left(1S\right)$, $\psi \left(2S\right)$, and ${\rm Y}$ states in the proton-nucleus collisions in the CERN Large Hadron Collider (LHC) energies. Predictions for the rapidity distributions are presented using the color dipole formalism and including saturation effects that are expected to be relevant at high energies. Calculations are done at the energy 5.02 TeV and also for the next LHC run at 8.8 TeV in proton-lead mode. Discussion is performed on the main theoretical uncertainties associated to the calculations.

Background: The physics of open quantum systems is an interdisciplinary area of research. The nuclear “openness” manifests itself through the presence of the many-body continuum representing various decay, scattering, and reaction channels. As the radioactive nuclear beam experimentation extends the known nuclear landscape toward the particle drip lines, the coupling to the continuum space becomes exceedingly more important. Of particular interest are weakly bound and unbound nuclear states appearing around particle thresholds. Theories of such nuclei must take into account their open quantum nature.

Purpose: To describe open quantum systems, we introduce a complex-scaling (CS) approach in the Slater basis. We benchmark it with the complex-energy Gamow shell model (GSM) by studying energies and wave functions of the bound and unbound states of the two-neutron halo nucleus ${}^6$He viewed as an $\alpha +n+n$ cluster system.

Methods: Both CS and GSM approaches are applied to a translationally invariant Hamiltonian with the two-body interaction approximated by the finite-range central Minnesota force. In the CS approach, we use the Slater basis, which exhibits the correct asymptotic behavior at large distances. To extract particle densities from the back-rotated CS solutions, we apply the Tikhonov regularization procedure, which minimizes the ultraviolet numerical noise.

Results: We show that the CS-Slater method is both accurate and efficient. Its equivalence to the GSM approach has been demonstrated numerically for both energies and wave functions of ${}^6$He. One important technical aspect of our calculation was to fully retrieve the correct asymptotic behavior of a resonance state from the complex-scaled (square-integrable) wave function. While standard applications of the inverse complex transformation to the complex-rotated solution provide unstable results, the stabilization method fully reproduces the GSM benchmark. We also propose a method to determine the smoothing parameter of the Tikhonov regularization.

Conclusions: The combined suite of CS-Slater and GSM techniques has many attractive features when applied to nuclear problems involving weakly bound and unbound states. While both methods can describe energies, total widths, and wave functions of nuclear states, the CS-Slater method—if it can be applied—can provide additional information about partial energy widths associated with individual thresholds.

We study the two-neutron decay of the unbound ${}^{26}\mathrm{O}$ nucleus with a three-body model assuming an inert ${}^{24}\mathrm{O}$ core and two valence neutrons. We first discuss the importance of the neutron-neutron final state interaction in the observed decay energy spectrum. We then show that the energy and and angular distributions for the two emitted neutrons manifest a clear evidence for the strong neutron-neutron correlation in the three-body resonance state. In particular, we find an enhancement of two-neutron emission in back-to-back directions. This is interpreted as a consequence of dineutron correlation, with which the two neutrons are spatially localized before the emission.

The properties of hot symmetric nuclear matter for a wide range of densities and temperatures are investigated by employing the $A{V}_{14}$ potential within the lowest order constrained variational (LOCV) method with the inclusion of a phenomenological three-body force as well as relativistic corrections. The relativistic corrections of many-body kinetic energies as well as the boot interaction corrections are presented for a wide range of densities and temperatures. The free energy, pressure, incompressibility, and other thermodynamic quantities of symmetric nuclear matter are obtained and discussed. The critical temperature is found, and the liquid-gas phase transition is analyzed both with and without the inclusion of three-body forces and relativistic corrections in the LOCV approach. It is shown that the critical temperature is strongly affected by the three-body forces but does not depend on the relativistic corrections. Finally, the results obtained in the present study are compared with other many-body calculations and experimental predictions.

One-neutron halo nuclei, composed of a weakly bound particle coupled to a core nucleus, are studied within a particle-plus-core model. A semi-microscopic method to generate the two-body Hamiltonian of such a system, including core excitation, is proposed. The method consists of generating the spin-independent part of the valence-core interaction using a single-folding procedure, convoluting a realistic nucleon-nucleon (NN) interaction with the core transition densities. The latter are calculated with the antisymetrized molecular dynamics (AMD) method. The prescription is applied to the well known halo nucleus, ${}^{11}$Be, as a test case. The results show an important predictive power that opens a door to the understanding of other lesser known halo nuclei. In order to show the potential usefulness of the method, it is applied to analyze the structure of ${}^{19}$C.

We extend effective field theory to the case of spontaneous symmetry breaking in genuinely finite quantum systems such as small superfluid systems, molecules, or atomic nuclei and focus on deformed nuclei. In finite superfluids, symmetry arguments alone relate the spectra of systems with different particle numbers. For systems with nonspherical intrinsic ground states such as atomic nuclei or molecules, symmetry arguments alone yield the universal features of the low-lying excitations as vibrations that are the heads of rotational bands. The low-lying excitations in deformed nuclei differ from those in molecules because of symmetry properties caused by pairing.

It was pointed out that the isoscalar dipole strength distribution in nuclei contributes to the Schiff moment. The nuclear Schiff moment is essential in the mechanism that induces parity and time-reversal violations in the atom. In this paper, we explore, theoretically, the properties and systematics of the isoscalar dipole in nuclei with an emphasis on the low-energy strength and the inverse energy-weighted sum which determines the Schiff moment. We also study the influence of the isovector dipole strength distribution on the Schiff moment. The influence of large neutron excess in exotic nuclei is examined. The centroid energies of the isoscalar giant dipole resonance and the overtone of the isovector giant dipole resonance are given for a wide range of nuclei.

An effective, nonrelativistic quantum field theory for the $dt\to n\alpha$ fusion reaction in the low-energy, resonance region is presented. The theory assumes that the reaction is dominated by an intermediate ${}^5{\mathrm{He}}^{*}$ unstable spin-$3/2^{+}$ resonance. It involves two parameters in the coupling of the $dt$ and $n\alpha$ particles to the unstable resonant state and the resonance energy level—only three real parameters in all. All Coulomb corrections to this process are computed. The resultant field theory is exactly solvable and provides an excellent description of the $dt$ fusion process.

We study the zero channel radius limit of Wigner's $R$-matrix theory for two cases and show that it corresponds to nonrelativistic effective quantum field theory. We begin with the simple problem of single-channel $np$ elastic scattering in the ${}^1{S}_0$ channel. The dependence of the $R$-matrix width $g^2$ and level energy $E_{\lambda }$ on the channel radius $a$ for fixed scattering length $a_0$ and effective range $r_0$ is determined. It is shown that these quantities have a simple pole for a critical value of the channel radius, $a_p=a_p(a_0,r_0)$. The ${}^3$H${(d,n)}^4$He reaction cross section, analyzed with a two-channel effective field theory in the previous paper [Phys. Rev. C 89, 014622 (2014)], is then examined using a two-channel, single-level $R$-matrix parametrization. The resulting $S$ matrix is shown to be identical in these two representations in the limit that $R$-matrix channel radii are taken to zero. This equivalence is established by giving the relationship between the low-energy constants of the effective field theory (couplings $g_c$ and mass $m_{*}$) and the $R$-matrix parameters (reduced width amplitudes ${\gamma }_c$ and level energy $E_{\lambda }$). An excellent three-parameter fit to the observed astrophysical factor $\overline{S}$ is found for “unphysical” values of the reduced widths, ${\gamma }_c^2<0$.

Based on previous studies that support the important role of the $N^{*}\left(2120\right)D_{13}$ resonance in the $\gamma p\to K^{+}\Lambda \left(1520\right)$ reaction, we make a re-analysis of this $\Lambda \left(1520\right)$ photoproduction reaction taking into account the recent CLAS differential cross-section data. In addition to the contact, $t$-channel $\overline{K}$ exchange, $s$-channel nucleon pole, and $N^{*}\left(2120\right)$ [previously called $N^{*}\left(2080\right)$] resonance contributions, which have been considered in previous works, we also study the $u$-channel $\Lambda \left(1115\right)$ hyperon pole term. The latter mechanism has always been ignored in all theoretical analysis, which has mostly relied on the very forward $K^{+}$ angular LEPS data. It is shown that when the contributions from the $N^{*}\left(2120\right)$ resonance and the $\Lambda \left(1115\right)$ hyperon are taken into account, both the new CLAS and the previous LEPS data can be simultaneously described. We also show that the contribution from the $u$-channel $\Lambda \left(1115\right)$ pole term produces an enhancement for large $K^{+}$ angles, and it becomes more and more relevant as the photon energy increases, being essential to describe the CLAS differential cross sections at backward angles. Furthermore, we find that the new CLAS data also favor the existence of the $N^{*}\left(2120\right)$ resonance and that these measurements can be used to further constrain its properties.

In this work, we propose a new description of nuclear spectroscopy based on the analysis of a rather complete set of observables, using the multiparticle-multihole configuration mixing and the D1S Gogny interaction. The application to the even-even $sd$-shell nuclei, for both ground and 0${}_2^{+}$, 1${}_1^{+}$, 2${}_1^{+}$, 2${}_2^{+}$, 3${}_1^{+}$, 3${}_2^{+}$, 4${}_1^{+}$ excited states, clearly shows the pertinence of this approach. The standard deviation to experiment is $\sim$500 keV for two-nucleon separation energies and $\sim$400 keV for excitation energies. The calculated magnetic dipole moments and $B\left(M1\right)$ transition probabilities are in a very good agreement with experiment. Concerning the spectroscopic quadrupole moments and $B\left(E2\right)$ transition probabilities, the experimental trends are systematically reproduced. Only a lack of quadrupole collectivity appears. A solution to improve this expected defect is suggested.

We use properties of doubly magic nuclei and ab initio calculations of low-density neutron matter to constrain Skyrme equations of state for neutron-rich conditions. All of these properties are consistent with a Skyrme functional form and a neutron-matter equation of state that depends on three parameters. With a reasonable range for the neutron-matter effective mass, the values of the two other Skyrme parameters are well constrained. This leads to predictions for other quantities. The neutron skins for ${}^{208}\mathrm{Pb}$ and ${}^{48}\mathrm{Ca}$ are predicted to be 0.182(12) and 0.173(5) fm, respectively. Other results including the dipole polarizability are discussed.

Recent experimental data have demonstrated that ${}^{76}$Ge may be a rare example of a nucleus exhibiting rigid $\gamma$ deformation in the low-spin regime. In the present work, the experimental analysis is supported by microscopic calculations using the multi-quasiparticle triaxial projected shell model (TPSM) approach. It is shown that to best describe the data of both yrast and $\gamma$-vibrational bands in ${}^{76}$Ge, a rigid-triaxial deformation parameter $\gamma \approx {30}^{\circ }$ is required. TPSM calculations are discussed in conjunction with the experimental observations and also with the published results from the spherical shell model. The occurrence of a $\gamma \gamma$ band in ${}^{76}$Ge is predicted with the bandhead at an excitation energy of $\sim$2.5 MeV. We have also performed TPSM study for the neighboring Ge and Se isotopes and the distinct $\gamma$-soft feature in these nuclei is shown to result from configuration mixing of the ground-state with multi-quasiparticle states.

Nuclei with a central region of low nucleonic density, “bubble” nuclei, are studied. In particular, the possibility of bubbles in deformed nuclei is discussed, concentrating on experimentally accessible light nuclei. Utilizing the relativistic mean field (RMF) model we find favorable candidates in the prolately deformed ${}^{24}$Ne nucleus and the mirror nuclei ${}^{32}$Si and ${}^{32}$Ar with oblate shapes.