We report results of the equation of state of neutron matter in the low-density regime, where the Fermi wave vector ranges from $0.4⩽k_F⩽1.0\hspace{0.5em}{\mathrm{fm}}^{-1}$. Neutron matter in this regime is superfluid because of the strong and attractive interaction in the ${}^1{S}_0$ channel. The properties of this superfluid matter are calculated starting from a realistic Hamiltonian that contains modern two- and three-body interactions. The ground state energy and the ${}^1{S}_0$ superfluid energy gap are calculated using the auxiliary field diffusion Monte Carlo method. We study the structure of the ground state by looking at pair distribution functions as well as the Cooper-pair wave function used in the calculations.

In a hydrodynamic model, we have studied $J/\psi$ suppression and elliptic flow in $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider (RHIC) energy $\sqrt{s}=200$ GeV. At the initial time, $J/\psi$’s are randomly distributed in the fluid. As the fluid evolves in time, the free-streaming $J/\psi$’s are dissolved if the local fluid temperature exceeds a melting temperature $T_{J/\psi }$. Sequential melting of charmonium states (${\chi }_c$, ${\psi }^{\text{'}}$, and $J/\psi$), with melting temperatures $T_{{\chi }_c}=T_{{\psi }^{\text{'}}}\approx 1.2T_c$ and $T_{J/\psi }\approx 2T_c$ and a feed-down fraction $F\approx 0.3$, is consistent with the PHENIX data on $J/\psi$ suppression and near-zero elliptic flow for $J/\psi$’s. It is also shown that the model will require substantial regeneration of charmonium if the charmonium states dissolve at a temperature close to the critical temperatures, $T_{{\chi }_c}=T_{{\psi }^{\text{'}}}⩽T_c$ and $T_{J/\psi }\approx 1.2T_c$. The regenerated charmonium will have positive elliptic flow.

The frozen spin method can be effectively used for a high-precision measurement of the tensor electric and magnetic polarizabilities of the deuteron and other nuclei in storage rings. For the deuteron, this method would provide the determination of the deuteron’s polarizabilities with absolute precision of the order of ${10}^{-43}\hspace{0.5em}{\mathrm{cm}}^3$.

We have studied positive-parity states of ${}^{28}\mathrm{Si}$ using antisymmetrized molecular dynamics and multiconfiguration mixing with constrained variation. Applying constraints to the cluster distance and the quadrupole deformation of the variational calculation, we have obtained basis wave functions that have various structures such as $\alpha \text{−}$${}^{24}\mathrm{Mg}$ and ${}^{12}\mathrm{C}\text{−}{}^{16}\mathrm{O}$ cluster structures as well as deformed structures. Superposing those basis wave functions, we have obtained a oblate ground-state band, a $\beta$ vibration band, a normal-deformed prolate band, and a superdeformed band. It is found that the normal-deformed and superdeformed bands contain large amounts of the ${}^{12}\mathrm{C}\text{−}{}^{16}\mathrm{O}$ and $\alpha \text{−}$${}^{24}\mathrm{Mg}$ cluster components, respectively. The results also suggest the presence of two excited bands with the developed $\alpha \text{−}$${}^{24}\mathrm{Mg}$ cluster structure, where the intercluster motion and the ${}^{24}\mathrm{Mg}$-cluster deformation play important roles.

Proton decay from the $3\hslash \omega$ isoscalar giant dipole resonance (ISGDR) in ${}^{58}\mathrm{Ni}$ has been measured using the ($\alpha ,{\alpha }^{\text{'}}p$) reaction at a bombarding energy of 386 MeV to investigate its decay properties. We have extracted the ISGDR strength under the coincidence condition between inelastically scattered $\alpha$ particles at forward angles and decay protons emitted at backward angles. Branching ratios for proton decay to low-lying states of ${}^{57}\mathrm{Co}$ have been determined, and the results compared with predictions of recent continuum-RPA calculations. The final-state spectra of protons decaying to the low-lying states in ${}^{57}\mathrm{Co}$ were analyzed for a more detailed understanding of the structure of the ISGDR. It is found that there are differences in the structure of the ISGDR as a function of excitation energy.

The frequency ratio of ${}^6\mathrm{Li}$ to ${}^7\mathrm{Li}$ was measured using the TITAN Penning trap mass spectrometer. This measurement resolves a $16$-ppb discrepancy between the ${}^6\mathrm{Li}$ mass of 6.015 122 795(16) u from the Atomic Mass Evaluation 2003 (AME03), which is based on a measurement by JILATRAP, and the more recent measurement of 6.015 122 890(40) u by SMILETRAP. Our measurement agrees with SMILETRAP and a more precise mass value for ${}^6\mathrm{Li}$ of 6.015 122 889(26) u is presented along with systematic evaluations of the measurement uncertainties. This result makes ${}^6\mathrm{Li}$ a solid anchor point for future mass measurements on highly charged ions with $m/q~6$.

Using a transport model coupled with a phase-space coalescence afterburner, we study the triton-${}^3\mathrm{He}$ ($t\text{−}$${}^3\mathrm{He}$) ratio with both relative and differential transverse flows in semicentral ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ reactions at a beam energy of $400$ MeV/nucleon. The neutron-proton ratios with relative and differential flows are also discussed as a reference. We find that similar to the neutron-proton pairs, the $t\text{−}$${}^3\mathrm{He}$ pairs also carry interesting information regarding the density dependence of the nuclear symmetry energy. Moreover, the nuclear symmetry energy affects more strongly the $t\text{−}$${}^3\mathrm{He}$ relative and differential flows than the ${\pi }^{-}/{\pi }^{+}$ ratio in the same reaction. The $t\text{−}$${}^3\mathrm{He}$ relative flow can be used as a particularly powerful probe of the high-density behavior of the nuclear symmetry energy.

We assume that, in equilibrium, nuclear matter at reduced density and moderate finite temperature breaks up into many fragments. Strong support for this assumption is provided by data accumulated from intermediate-energy heavy ion collisions. The breakup of hot and expanded nuclear matter according to the rules of equilibrium statistical mechanics is the multifragmentation model, which gives a first-order phase transition. This is studied in detail here. Phase-equilibrium lines for different degrees of asymmetry are computed.

The surrogate ratio method (SRM) was employed in the first experimental determination of the ${}^{231}\mathrm{Th}$$(n,f)$ cross section, relative to the ${}^{235}\mathrm{U}$$(n,f)$ cross section, over an equivalent neutron energy range of $360$ keV to $10$ MeV. The ${}^{230}\mathrm{Th}$$(n,f)$ cross section was also deduced using the SRM, relative to the ${}^{234}\mathrm{U}$$(n,f)$ cross section, over an equivalent neutron energy range of $220$ keV to $25$ MeV. The desired compound nuclei were populated using (${}^3\mathrm{He}$,${}^3\mathrm{He}$$\text{'}$) and (${}^3\mathrm{He}$$,\alpha$) reactions on targets of ${}^{232}\mathrm{Th}$ and ${}^{236}\mathrm{U}$ and relative fission decay probabilities were measured. The surrogate ${}^{230,231}\mathrm{Th}$$(n,f)$ cross sections were compared to cross section evaluations and directly-measured experimental data, where available.

We study hadronic nonlinear point-coupling (NLPC) models which reproduce numerically the binding energy, the incompressibility, and the nucleon effective mass at the nuclear matter saturation obtained by different nonlinear Walecka (NLW) models. We have investigated their behaviors as functions of the nuclear matter density to observe how they deviate from known NLW models. In our study we present a meson-exchange modified nonlinear Walecka model (MNLW) which exactly underlies a nonlinear point-coupling model (NLPC) presenting third- and fourth-order scalar density self-couplings. A discussion about naive dimensional analysis (NDA) and naturalness is also provided for a large class of NLW and NLPC models. At finite temperature, critical and flash parameters of both approaches are presented.

We introduce a microscopic approach for calculating the excitation energies of systems formed during heavy-ion collisions. The method is based on time-dependent Hartree-Fock (TDHF) theory and allows the study of the excitation energy as a function of time or ion-ion separation distance. We discuss how this excitation energy is related to the estimate of the excitation energy using the reaction $Q$-value, as well as its implications for dinuclear precompound systems formed during heavy-ion collisions.

A model is investigated that displays a picture of the symmetry energy as an energy of rotation in isospace of a Cooper pair condensate, briefly “superfluid isorotation.” The Hamiltonian is isobarically invariant and has a one- and a two-nucleon term, where the two-nucleon interaction is composed of an isovector pairing force and an interaction of isospins. It is analyzed in the Hartree-Bogolyubov plus random-phase approximation (RPA). The Hartree-Bogolyubov energy minus Lagrangian multiplier terms proportional to the number of valence nucleons and the $z$ component of the isospin is shown to be locally minimized by a product of neutron and proton Bardeen-Cooper-Schrieffer states. The equations of the RPA can be reduced to independent equations for two-neutron, two-proton, and neutron-proton quasiparticle pairs. In each of these spaces, they have a Nambu-Goldstone solution due to the global gauge invariance and isobaric invariance of the Hamiltonian. Except for the Nambu-Goldstone solutions, the RPA solutions are independent of the strength of the isospin interaction. If, in one space, the pertinent single-nucleon spectrum has a particle-hole symmetry, the RPA solutions are twofold degenerate except for the Nambu-Goldstone solution and one more solution. In an idealized case of infinitely many equidistant single-nucleon levels, the one-nucleon term in the Hamiltonian and the isospin interaction contribute terms in the symmetry energy quadratic in the isospin $T$. The pairing force and the two-neutron and two-proton RPA correlation energies do not contribute. The contribution of the neutron-proton correlation energy is dominated by the Nambu-Goldstone solution, which gives a linear term that makes the total symmetry energy proportional to $T(T+1)$. The rest of this contribution is negative and can be written as the difference of two terms of the form $\sqrt{(aT){}^2+b^2}-b$. Observations reported from Skyrme force calculations are discussed in the light of these results. Calculations with deformed Woods-Saxon single-nucleon levels give results similar to those of the idealized case. In calculations for the mass numbers $A=56$ and $A=100$ with spherical Woods-Saxon levels, the promotion of nucleons across magic gaps in the single-nucleon spectrum and the onset of superfluidity with the departure from magicity give rise to large linear terms in the symmetry energy. The calculations with Woods-Saxon single-nucleon levels reproduce surprisingly well the empirical symmetry energy. An experimental signature of superfluid isorotation is discussed.

High spin excited states in the neutron-rich nuclei ${}^{137}\mathrm{I}$ and ${}^{139}\mathrm{Cs}$ were investigated from a study of the prompt $\gamma$ rays emitted in the spontaneous fission of ${}^{252}\mathrm{Cf}$ with the Gammasphere detector array. Ten new excited levels with $18$ new deexciting transitions were observed in ${}^{139}\mathrm{Cs}$ and the level scheme of ${}^{139}\mathrm{Cs}$ was extended up to $4670$ keV. Spins and parities of levels in ${}^{139}\mathrm{Cs}$ were firmly assigned up to $25/2^{+}$. Three new levels were found in ${}^{137}\mathrm{I}$. Shell model calculations were performed to interpret the experimental results. A good agreement between theory and experiment in both nuclei was found.

We discuss the variation of the nuclear matrix element (NME) for the neutrinoless double beta ($0\nu \beta \beta$) decay of ${}^{76}\mathrm{Ge}$ when the wave functions are constrained to reproduce the experimental occupancies of the two nuclei involved in the transition. In the interacting shell model description the value of the NME is enhanced about 15% compared to previous calculations, whereas in the QRPA the NME’s are reduced by 20%–30%. This diminishes the discrepancies between both approaches. In addition, we discuss the effect of the short-range correlations on the NME in light of the recently proposed parametrizations based on a consistent renormalization of the $0\nu \beta \beta$ transition operator.

Closed shell-nuclei are described employing an interaction model which is based on the low-momentum interaction $V_{\mathrm{low}\text{−}\mathrm{k}}$. This effective two-body interaction which is determined to reproduce the nucleon-nucleon (NN) scattering data at energies below the pion threshold is supplemented by a density-dependent contact interaction fitted to reproduce the saturation properties of infinite nuclear matter within the Hartree-Fock approach. It is demonstrated that corresponding calculations for closed shell nuclei using this interaction model reproduce the bulk properties of these nuclei in a basis of plane waves discretized in a spherical box of appropriate size. This plane wave basis is very appropriate to describe weakly bound nuclei close to the neutron drip line and the transition from discrete nuclei to homogeneous matter which is supposed to occur, e.g., in the crust of neutron stars.

It is shown that the momentum-dependent kaon-antikaon interactions generated via vector-meson exchange from the standard ${\mathrm{SU}}_V(3)\times {\mathrm{SU}}_A(3)$ interaction Lagrangian lead to a nonlocal potential in coordinate space that can be incorporated without approximation into a nonrelativistic version of the Bethe-Salpeter wave equation containing a radial-dependent effective kaon mass appearing in a fully symmetrized kinetic energy operator, in addition to a local potential. Estimates of the mass and decay widths of $f_0(980)$ and $a_0(980)$, considered as $K\overline{K}$ molecules of isospin $0$ and $1$, as well as for $K^{+}{K}^{-}$ atomic bound states (kaonium) are presented and compared with previous studies of a similar nature. It is argued that without a better knowledge of hadronic form factors it is not possible to distinguish between the molecular versus elementary particle models for the structure of the light scalar mesons.

Within a parton transport model, we show that diffusion wakes and Mach cone wakes produced from energy loss by a fast parton propagating in the quark-gluon plasma lead to the observed azimuthal angular correlations of hadrons in central $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC. The magnitude and shape of the wakes are shown to be sensitive measures of the initial parton density and the parton scattering cross section. The shear viscosity to entropy density ratio, $\eta /s$, of the plasma is found to be remarkably similar to the lower bound $\eta /s=1/4\pi$ obtained in the AdS/CFT conjecture.

The level density and $\gamma$-ray strength function of ${}^{45}\mathrm{Ti}$ have been determined by use of the Oslo method. The particle-$\gamma$ coincidences from the ${}^{46}\mathrm{Ti}$$(p,d\gamma )$${}^{45}\mathrm{Ti}$ pick-up reaction with $32$-MeV protons are utilized to obtain $\gamma$-ray spectra as function of excitation energy. The extracted level density and strength function are compared with models, which are found to describe these quantities satisfactorily. The data do reveal no single-particle energy gaps of the underlying doubly magic ${}^{40}\mathrm{Ca}$ core, probably due to the strong quadruple deformation.

We propose a microscopic approach to three-body continuum states in the hyperspherical formalism. The $A$-nucleon wave functions are defined in the generator coordinate method, based on a three-cluster approximation of the system. We develop a semianalytical treatment of the matrix elements, limited to $s$ clusters. This allows a fast calculation, as well as a direct interpretation of the wave functions, in terms of nucleon exchanges. We apply the method to the $\alpha +n+n$ three-body phase shifts and confirm the existence of broad structures in the $0^{+}$ and $1^{-}$ partial waves at low energies.

We have studied neutron-rich calcium isotopes in terms of the shell model, employing a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential. The short-range repulsion of the potential is renormalized by way of the $V_{\mathrm{low}-\mathrm{k}}$ approach. The calculated results are in very good agreement with the available experimental data, thus supporting our predictions for the hitherto unknown spectra of ${}^{53-56}\mathrm{Ca}$ nuclei. In this context, the possible existence of an $N=34$ shell closure is discussed.