Background: It is known that some well established parametrizations of the nuclear energy density functional (EDF) do not always lead to converged results for nuclei. Earlier studies point towards the existence of a qualitative link between this finding and the appearance of finite-size instabilities of symmetric nuclear matter (SNM) near saturation density when computed within the random phase approximation (RPA).

Purpose: We aim to establish a stability criterion based on computationally friendly RPA calculations that can be incorporated into fitting procedures of the coupling constants of the EDF. Therefore, a quantitative and systematic connection between the impossibility to converge self-consistent calculations of nuclei and the occurrence of finite-size instabilities in SNM is investigated for the scalar-isovector ($S=0$, $T=1$) instability of the standard Skyrme EDF.

Results: Tuning the coupling constant $C_1^{\rho \Delta \rho }$ of the gradient term that triggers scalar-isovector instabilities of the standard Skyrme EDF, we find that the occurrence of instabilities in finite nuclei depends strongly on the numerical scheme used to solve the self-consistent mean-field equations. Once the critical value of the coupling constant $C_1^{\rho \Delta \rho }$ is determined in nuclei, one can extract the corresponding lowest density ${\rho }_{\text{crit}}$ at which a pole appears at zero energy in the RPA response function.

Conclusions: Instabilities of finite nuclei can be artificially hidden due to the choice of inappropriate numerical schemes or overly restrictive, e.g., spherical, symmetries. Our analysis suggests a twofold stability criterion to avoid scalar-isovector instabilities.

The extraction of detailed nuclear structure information from transfer reactions requires reliable, well-normalized data, as well as optical potentials and a theoretical framework demonstrated to work well in the relevant mass and beam energy ranges. It is rare that the theoretical ingredients can be tested well for exotic nuclei owing to the paucity of data. The halo nucleus ${}^{11}$Be has been examined through the ${}^{10}$Be($d,p$) reaction in inverse kinematics at equivalent deuteron energies of $12,15,18,$ and $21.4$ MeV. Elastic scattering of ${}^{10}$Be on protons was used to select optical potentials for the analysis of the transfer data. Additionally, data from the elastic and inelastic scattering of ${}^{10}$Be on deuterons was used to fit optical potentials at the four measured energies. Transfers to the two bound states and the first resonance in ${}^{11}$Be were analyzed using the finite-range adiabatic wave approximation. Consistent values of the spectroscopic factor of both the ground and first excited states were extracted from the four measurements, with average values of 0.71(5) and 0.62(4), respectively. The calculations for transfer to the first resonance were found to be sensitive to the size of the energy bin used and therefore could not be used to extract a spectroscopic factor.

The applicability of Coulomb dissociation reactions to determine the cross section for the inverse neutron capture reaction was explored using the reaction ${}^8$Li($\gamma$,$n$)${}^7$Li. A 69.5 MeV/nucleon ${}^8$Li beam was incident on a Pb target, and the outgoing neutron and ${}^7$Li nucleus were measured in coincidence. The deduced ($n$,$\gamma$) excitation function is consistent with data for the direct capture reaction ${}^7$Li($n$,$\gamma$)${}^8$Li and with low-energy effective field theory calculations.

In the projected-Hartree-Fock-Bogoliubov (PHFB) model, uncertainties in the nuclear transition matrix elements for the neutrinoless double-$\beta$ decay of ${}^{94,96}$Zr, ${}^{98,100}$Mo, ${}^{104}$Ru, ${}^{110}$Pd, ${}^{128,130}$Te, and ${}^{150}$Nd isotopes within mechanisms involving light Majorana neutrinos, classical Majorons, and sterile neutrinos are statistically estimated by considering sets of 16 (24) matrix elements calculated with four different parametrizations of the pairing plus multipolar type of effective two-body interaction, two sets of form factors, and two (three) different parametrizations of Jastrow type of short-range correlations. In the mechanisms involving the light Majorana neutrinos and classical Majorons, the maximum uncertainty is about 15% and in the scenario of sterile neutrinos, it varies in between approximately 4 (9)%–20 (36)% without(with) Jastrow short range correlations with the Miller-Spencer parametrization, depending on the considered mass of the sterile neutrinos.

The azimuthal anisotropy coefficients $v_2$ and $v_4$ of ${\pi }^0$ and $\eta$ mesons are measured in Au + Au collisions at $\sqrt{s_{\mathit{\text{NN}}}}=200$ GeV as a function of transverse momentum $p_T$ (1–14 GeV/$c$) and centrality. The extracted $v_2$ coefficients are found to be consistent between the two meson species over the measured $p_T$ range. The ratio of $v_4/v_2^2$ for ${\pi }^0$ mesons is found to be independent of $p_T$ for 1–9 GeV/$c$, implying a lack of sensitivity of the ratio to the change of underlying physics with $p_T$. Furthermore, the ratio of $v_4/v_2^2$ is systematically larger in central collisions, which may reflect the combined effects of fluctuations in the initial collision geometry and finite viscosity in the evolving medium.

The formation of complex nonuniform phases of nuclear matter, known as nuclear pasta, is studied with molecular dynamics (MD) simulations containing 51200 nucleons. A phenomenological nuclear interaction is used that reproduces the saturation binding energy and density of nuclear matter. Systems are prepared at an initial density of $0.10{\mathrm{fm}}^{-3}$ and then the density is decreased by expanding the simulation volume at different rates to densities of $0.01{\mathrm{fm}}^{-3}$ or less. An originally uniform system of nuclear matter is observed to form spherical bubbles (“swiss cheese”), hollow tubes, flat plates (“lasagna”), thin rods (“spaghetti”) and, finally, nearly spherical nuclei with decreasing density. We explicitly observe nucleation mechanisms, with decreasing density, for these different pasta phase transitions. Topological quantities known as Minkowski functionals are obtained to characterize the pasta shapes. Different pasta shapes are observed depending on the expansion rate. This indicates nonequilibrium effects. We use this to determine the best ways to obtain lower energy states of the pasta system from MD simulations and to place constraints on the equilibration time of the system.

Based on the Boltzmann-Langevin transport model, in which the isospin and momentum-dependent potential is incorporated, we investigate the neutron-proton effective mass splitting in central reactions using Sn isotopes at 50 MeV/nucleon. It is found that the transverse momentum, rapidity, and kinetic energy distributions of free neutron over proton ratio are sensitive to the neutron-proton effective mass splitting, especially at higher transverse momenta, at higher kinetic energies, and at larger rapidities. The calculated results favor the effective mass of neutrons less than the one of protons in comparison with the experimental data of Famiano et al. [Phys. Rev. Lett. 97, 052701 (2006)].

Recently I proposed [Jia, Phys. Rev. C 88, 044303 (2013)] a new method for solving the pairing Hamiltonian with the pair-condensate wave-function ansatz based on the Heisenberg equations of motion for the density matrix operators. In this work an improved version is given by deriving the relevant equations more carefully. I evaluate both versions in a large ensemble with random interactions, and the accuracy of the methods is given statistically in terms of root-mean-square derivations from the exact results. The widely used variational calculation is also done and the results and computing-time costs are compared.

We study the collision energy dependence of elliptic flow $v_2$ and triangular flow $v_3$ in Au+Au collisions within the energy range $\sqrt{s_{\mathit{NN}}}=5–200$ GeV, utilizing a transport + hydrodynamics hybrid model. The transport part is described by the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) approach, combined with an intermediate (3+1)-dimensional ideal hydrodynamical evolution phase using a chiral model equation of state. We find the decrease of $v_2$ produced by hydrodynamics at lower collision energies to be partially compensated by the transport dynamics. This does not apply to $v_3$, which falls to 0 in midcentral collisions at $\sqrt{s_{\mathit{NN}}}=5$ GeV. We conclude that the triangular flow provides the clearer signal for the formation of low-viscous fluid in heavy-ion collisions.

We study the dynamics of color fields as generated by simple configurations of relativistic particles with Abelian and non-Abelian [SU(2)] charges in the classical limit. We find that chromodynamic (non-Abelian) systems generally show Coulomb-like features by analogy with electrodynamics. A peculiar feature in the non-Abelian case is the additional strength of the chromoelectric and chromomagnetic fields caused by the contribution of changing the color charge. This change of color SU(2) charges results in a rotation of the color vector, which is getting very fast at close partonic distances. The presence of this non-Abelian additional term in the chromoelectric and chromomagnetic fields creates a color charge glow, which is manifested as a distinct color wave disturbance arising due to the finite distance at which the color interaction becomes active. This situation may be relevant to the hadronization phase in ultrarelativistic heavy-ion collisions, where the partonic state is governed by strong local color fluctuations.

To study partial restoration of the chiral symmetry at finite density, we investigate the density corrections of the chiral condensate up to the next-to-leading order of density expansion using the chiral Ward identity and an in-medium chiral perturbation theory. In our study, we assume that all the in-vacuum quantities for the pion, the nucleon, and the $\pi N$ interaction are determined in vacuum and focus on density expansion of the in-medium physical quantities. We perform diagrammatic analysis of the correlation functions which provide the in-medium chiral condensate. This density expansion scheme shows that the medium effect to the chiral condensate beyond the linear density comes from density corrections to the $\pi N$ $\sigma$ term as a result of the interactions between pion and nucleon in nuclear matter. We also discuss that higher-density contributions beyond the order of ${\rho }^2$ cannot be fixed only by the in-vacuum $\pi N$ dynamics and we encounter divergence in the calculation of the ${\rho }^2$-order corrections of the chiral condensate. To remove the divergence, we need $NN$ two-body contact interaction, which can be fixed in vacuum.

The $\beta$ decay of the most neutron-rich iron isotopes was investigated, leading to the first determination of the ${}^{72}$Fe half-life and new measurements of the half-lives of ${}^{69-71}$Fe. The experimental results are compared with theoretical predictions and presented in the context of the weak astrophysical rapid neutron capture process.

Fast spectrum neutron-induced fission cross-section data for transuranic isotopes are of special demand from the nuclear data community. In particular highly accurate data are needed for the new generation IV nuclear applications. The aim is to obtain precise neutron-induced fission cross sections for ${}^{240}$Pu and ${}^{242}$Pu. To do so, accurate data on spontaneous fission half-lives must be available. Also, minimizing uncertainties in the detector efficiency is a key point. We studied both isotopes by means of a twin Frisch-grid ionization chamber with the goal of improving the present data on the neutron-induced fission cross section. For the two plutonium isotopes the high $\alpha$-particle decay rates pose a particular problem to experiments due to piling-up events in the counting gas. Argon methane and methane were employed as counting gases, the latter showed considerable improvement in signal generation due to its higher drift velocity. The detection efficiency for both samples was determined, and improved spontaneous fission half-lives were obtained with very low statistical uncertainty (0.13% for ${}^{240}$Pu and 0.04% for ${}^{242}$Pu): for ${}^{240}$Pu, $T_{1/2,SF}=1.165\times {10}^{11}$ yr $(1.1\%)$, and for ${}^{242}$Pu, $T_{1/2,SF}=6.74\times {10}^{10}$ yr $(1.3\%)$. Systematic uncertainties are due to sample mass (0.4% for ${}^{240}$Pu and 0.9% for ${}^{242}$Pu) and efficiency (1%).

Beam asymmetries for the reactions $\gamma p\to p{\pi }^0$ and $\gamma p\to n{\pi }^{+}$ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged, linearly polarized photon beam with energies from 1.102–1.862 GeV. A Fourier moment technique for extracting beam asymmetries from experimental data is described. The results reported here possess greater precision and finer energy resolution than previous measurements. Our data for both pion reactions appear to favor the SAID and Bonn-Gatchina scattering analyses over the older Mainz MAID predictions. After incorporating the present set of beam asymmetries into the world database, exploratory fits made with the SAID analysis indicate that the largest changes from previous fits are for properties of the $\Delta \left(1700\right)3/2^{-}$ and $\Delta \left(1905\right)5/2^{+}$ states.

Globular clusters represent some of the oldest stellar aggregations in the universe. As such, they are used as testing grounds for theories of stellar evolution and nucleosynthesis. Astronomical observations have shown star-to-star abundance variations in light-mass elements in all galactic globular clusters that are not predicted by standard stellar evolution models. In particular, there exists a pronounced anticorrelation between Na and O in the cluster stars that is not observed in field stars of similar evolutionary state. The abundance of Na is regulated in part by the ${}^{23}\mathrm{Na}$$+p$ reaction, which is also a bridge between the NeNa and the MgAl mass regions, but the ${}^{23}\mathrm{Na}{(p,\gamma )}^{24}\mathrm{Mg}$ reaction rate is very uncertain for burning temperatures relevant to stars on the red giant and asymptotic giant branches. This uncertainty arises from an expected but unobserved resonance at $E_r^{\mathrm{c}.\mathrm{m}.}$ = 138 keV. The resonance strength upper limit has been determined to be $\omega \gamma$${}_{\mathrm{UL}}$(138 keV) $\le 5.17\times {10}^{-9}$ eV with indications of a signal at the 90% confidence level. New reaction rates have been calculated for the ${}^{23}\mathrm{Na}{(p,\gamma )}^{24}\mathrm{Mg}$ and ${}^{23}\mathrm{Na}{(p,\alpha )}^{20}\mathrm{Ne}$ reactions and the recommended value for the ${}^{23}\mathrm{Na}{(p,\gamma )}^{24}\mathrm{Mg}$ rate has been reduced by over an order of magnitude at $T_9$ = 0.07. This will have implications for the processing of material between the NeNa and MgAl mass regions.

Background: The (spin and isospin zero) $\alpha$-particle is an efficient projectile for the excitation of the isoscalar, natural-parity states of ${}^{12}$C. Among those states that have pronounced $\alpha$-cluster structure, the Hoyle state ($0_2^{+}$ state at 7.65 MeV) has been observed in many ($\alpha ,{\alpha }^{\prime }$) experiments while the second $2^{+}$ state of ${}^{12}$C, predicted at $E_x\approx 10$ MeV as an excitation of the Hoyle state, has not been observed until a recent high-precision experiment of the $\alpha +{}^{12}$C scattering at $E_{\alpha }=386$ MeV. A plausible reason is a strong population of the narrow $3_1^{-}$ state at 9.64 MeV and broad 0${}_3^{+}$ resonance at 10.3 MeV that hinders the weak $2_2^{+}$ peak in the ($\alpha ,{\alpha }^{\prime }$) spectrum.

Purpose: The accurate determination of the electric $E\lambda$ transition strengths of the isoscalar states of ${}^{12}$C, including an $E2$ component at $E_x\approx 10$ MeV that can be assigned to the $2_2^{+}$ state, based on a detailed folding-model + coupled-channels analysis of the ($\alpha ,{\alpha }^{\prime }$) data measured at $E_{\alpha }=240$ and 386 MeV.

Method: The complex optical potential and inelastic form factor given by the folding model for the $\alpha +{}^{12}$C scattering are used to calculate the ($\alpha ,{\alpha }^{\prime }$) cross sections for the known isoscalar states of ${}^{12}$C in an elaborate coupled-channels approach. The strengths of the form factors for these states are then fine tuned against the ($\alpha ,{\alpha }^{\prime }$) data to deduce the corresponding $E\lambda$ transition strengths.

Results: A significant $E2$ transition strength has been obtained for the $2_2^{+}$ state from the present analysis of the ($\alpha ,{\alpha }^{\prime }$) data measured at $E_{\alpha }=240$ and 386 MeV. The $E\lambda$ transition strengths of the $0_2^{+},3_1^{-},0_3^{+},$ and $1_1^{-}$ states were also carefully deduced, and some difference from the results of earlier analyses has been found and qualitatively understood.

Conclusion: Despite a strong hindrance by the $3_1^{-}$ and $0_3^{+}$ excitations, the presence of the $2_2^{+}$ state in the ($\alpha ,{\alpha }^{\prime }$) spectra measured at $E_{\alpha }=240$ and 386 MeV has been consistently confirmed by the present folding-model + coupled-channels analysis.

After application of an analytical transformation, a new exact representation for the nuclear isospin-symmetry-breaking correction ${\delta }_C$ to superallowed $\beta$ decay is obtained. The correction is shown to be essentially the reciprocal of the square of an energy parameter ${\Omega }_M$ which characterizes the charge-exchange monopole strength distribution. The proportionality coefficient in this relation is determined by basic properties of the ground state of the even-even parent nucleus and should be reliably calculable in any realistic nuclear model. Therefore, the single parameter ${\Omega }_M$ contains all the information about the properties of excited $0^{+}$ states needed to describe ${\delta }_C$. This parameter can possibly be determined experimentally by charge-exchange reactions. Basic quantities of interest are calculated within the isospin-consistent continuum random phase approximation, and the values of ${\delta }_C$ are compared with the corresponding results from other approaches.

Background: Theoretical investigations of the structure of the low-lying states of nuclei with $Z\approx 100$ play an important role in understanding the properties of nuclei belonging to the new region of the nuclide chart which is available now for experimental study.

Purpose: We perform the calculations of the excitation energies and wave functions of the low-lying states of nuclei with $Z\approx 100$.

Methods: The quasiparticle-phonon model, which takes into account an interaction of the quasiparticles and phonons of different multipolarities, is used as a basis for the calculations.

Results: The excitation energies and the quasiparticle-phonon structure of the low-lying states with excitation energies up to 1200 keV of the odd-proton nuclei ${}^{239–251}$Bk, ${}^{243–255}$Es, ${}^{247–257}$Md, ${}^{253,255}$Lr, and ${}^{261,263}$Db are calculated.

Conclusions: It is shown that starting from 600 keV the excitation of the phonons and the quasiparticle-phonon interaction play an important role in the description of the properties of the excited states of nuclei with $Z\approx 100$.

We study ($p,2p$) and ($p,pn$) reactions at proton energies in the range of 100 MeV–1 GeV. Our purpose is to explore the most sensitive observables in unpolarized reactions with inverse kinematics involving radioactive nuclei. We formulate a model based on the eikonal theory to describe total cross sections and momentum distributions of the recoiled residual nucleus. The model is similar to the one adopted for knockout reactions with heavy ions. We show that momentum distributions are sensitive to the angular momentum of the ejected nucleon which can be used as an spectroscopic tool. The total cross sections are sensitive to the nucleon separation energies and to multiple scattering effects. Our calculations also indicate that a beam energy around 500 MeV/nucleon has a smaller dependence on the anisotropy of the nucleon-nucleon elastic scattering.

Recently, Elshamounty et al. performed a reanalysis of the surface temperature of the neutron star in the supernova remnant Cassiopeia A on the basis of Chandra data measured during the last decade and added a new data point. We show that all reliably known temperature data of neutron stars including those belonging to Cassiopeia A can be comfortably explained in our “nuclear medium cooling” scenario of neutron stars. The cooling rates account for medium-modified one-pion exchange in dense matter, polarization effects in the pair-breaking-formation processes operating on superfluid neutrons and protons paired in the $1S_0$ state, and other relevant processes. The emissivity of the pair-breaking-formation process in the $3P_2$ state is a tiny quantity within our scenario. Crucial for a successful description of the Cassiopeia A cooling proves to be the thermal conductivity from both the electrons and nucleons being reduced by medium effects. Moreover, we exploit an equation of state which stiffens at high densities due to an excluded volume effect and is capable of describing a maximum mass of $2.1M_{\odot }$, thus including the recent measurements of PSR J1614-2230 and PSR J0348+0432.