A ${}^{76}$Ge(${}^3$He,$t$)${}^{76}$As charge-exchange experiment at an incident energy of 420 MeV has been performed with an energy resolution of 30 keV. The Gamow-Teller GT${}^{-}$ strength distribution in ${}^{76}$As, which is the intermediate nucleus in the double-beta ($\beta \beta$) decay of ${}^{76}$Ge, has been extracted. An unusually strong fragmentation of the GT${}^{-}$ strength is observed even at low excitation energies of $E_x⩽5\mathrm{MeV}$. By combining the data with those for GT${}^{+}$ transitions from a recent ${}^{76}$Se($d$,${}^2$He)${}^{76}$As measurement, the nuclear matrix element for the ${}^{76}$Ge $2\nu \beta \beta$ decay has been evaluated. A lack of correlation among the GT transition strengths feeding the same levels from the two different directions is observed. The impact on the ${}^{76}$Ge $2\nu \beta \beta$ decay nuclear matrix element is discussed.

Based on the relativistic Hartree-Bogoliubov theory, the influence of the pairing interaction strength on the dineutron correlations and the crossover from superfluidity of neutron Cooper pairs in the ${}^1{S}_0$ channel to Bose-Einstein condensation of dineutron pairs is systematically investigated in the nuclear matter. The bare nucleon-nucleon interaction Bonn-B is taken in the particle-particle channel with an effective factor to simulate the medium effects and take into account the possible ambiguity of pairing force, and the effective interaction PK1 is used in the particle-hole channel. If the effective factor is larger than $1.10$, a dineutron Bose-Einstein condensation (BEC) state appears in the low-density limit, and if it is smaller than $0.85$, the neutron Cooper pairs are found totally in the weak coupling Bardeen-Cooper-Schrieffer (BCS) region. The reference values of several characteristic quantities which characterize the BCS-BEC crossover are obtained, respectively, from the dimensionless parameter $1/\left(k_{\mathrm{Fn}}a\right)$ with $a$ the scattering length and $k_{\mathrm{Fn}}$ the neutron Fermi momentum, the zero-momentum transfer density correlation function $D\left(0\right)$, and the effective chemical potential ${\nu }_{\mathrm{n}}$.

The BCS and/or Hartree-Fock-Bogoliubov theories are extended by treating the effect of four quasiparticle states perturbatively. The approach is tested on the pairing Hamiltonian, showing that it combines the advantage of standard perturbation theory, valid at low pairing strength, and of nonperturbative approaches breaking the particle number, valid at higher pairing strength. Including the restoration of particle number further improves the description of pairing correlation. In the presented test, the agreement between the exact solution and the combined perturbative plus projection is almost perfect. The proposed method scales friendly when the number of particles increases and provides a simple alternative to other more complicated approaches.

An iterative method we previously proposed to compute nuclear strength functions [Toivanen et al., Phys. Rev. C 81, 034312 (2010)] is developed to allow it to accurately calculate properties of individual nuclear states. The approach is based on the quasiparticle random-phase approximation (QRPA) and uses an iterative non-Hermitian Arnoldi diagonalization method where the QRPA matrix does not have to be explicitly calculated and stored. The method gives substantial advantages over conventional QRPA calculations with regards to the computational cost. The method is used to calculate excitation energies and decay rates of the lowest-lying $2^{+}$ and $3^{-}$ states in Pb, Sn, Ni, and Ca isotopes using three different Skyrme interactions and a separable Gaussian pairing force.

We study time-dependent coupled-cluster theory in the framework of nuclear physics. Based on Kvaal's bi-variational formulation of this method [S. Kvaal, J. Chem. Phys. 136, 194109 (2012)], we explicitly demonstrate that observables that commute with the Hamiltonian are conserved under time evolution. We explore the role of the energy and of the similarity-transformed Hamiltonian under real and imaginary time evolution and relate the latter to similarity renormalization group transformations. Proof-of-principle computations of ${}^4$He and ${}^{16}$O in small model spaces, and computations of the Lipkin model illustrate the capabilities of the method.

Neutrino-induced production (neutrinoproduction) of photons and pions from nucleons and nuclei is important for the interpretation of neutrino-oscillation experiments, as these photons and pions are potential backgrounds in the MiniBooNE experiment [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev. Lett. 100, 032301 (2008)]. These processes are studied at intermediate energies, where the $\Delta$(1232) resonance becomes important. The Lorentz-covariant effective field theory, which is the framework used in this series of studies, contains nucleons, pions, $\Delta$s, isoscalar scalar ($\sigma$) and vector ($\omega$) fields, and isovector vector ($\rho$) fields. The Lagrangian exhibits a nonlinear realization of (approximate) $\text{SU}{\left(2\right)}_L\otimes \text{SU}{\left(2\right)}_R$ chiral symmetry and incorporates vector meson dominance. In this paper, we focus on setting up the framework. Power counting for vertices and Feynman diagrams is explained. Because of the built-in symmetries, the vector current is automatically conserved, and the axial-vector current is partially conserved. To calibrate the axial-vector transition current $(N\leftrightarrow \Delta )$, pion production from the nucleon is used as a benchmark and compared to bubble-chamber data from Argonne and Brookhaven National Laboratories. At low energies, the convergence of our power-counting scheme is investigated, and next-to-leading-order tree-level corrections are found to be small.

We present neutrino cross sections on ${}^{13}$C. The charged-current cross sections leading to various states in the daughter ${}^{13}N$ and the neutral-current cross sections leading to various states in the daughter ${}^{13}$C are given. We also provide simple polynomial fits to those cross sections for quick estimates of the reaction rates. We briefly discuss possible implications for the current and future scintillator-based experiments.

The ${}^{149}$Ce nucleus has been studied via prompt $\gamma$-ray spectroscopy using the EUROGAM2 Ge array. The 3/2${}^{-}$ ground-state band has been extended to medium spins and the 3/2${}^{+}$ band has been connected to low-spin excitations established previously in ${\beta }^{-}$ decay. No evidence for parity doublets in ${}^{149}$Ce was found.

We show that within a hybrid two-stage approach one can explain novel experimental data on the production of hypernuclei emitted from projectile residues in relativistic ion collisions. This reaction proceeds via formation of intermediate moderately excited hypernuclear systems, which decay into conventional nuclei and hyperfragments afterward. With a similar reaction mechanism one can also obtain weakly bound exotic hypernuclei (such as $\Lambda n$ and H-dibaryons), which may not be easily accessible in other processes.

We calculate the parity-violating amplitudes in the $nd$ interaction with pionless effective field theory to leading order. Matching the parity-violating low-energy constants to the coefficients of the model by Desplanques, Donoghue, and Holstein we make numerical predictions for parity-violating observables. In particular, we give predictions for the spin rotation of a neutron on a deuteron target and for target and beam asymmetries in $nd$ scattering.

A new version is proposed for the universal empirical formula, EPAX, which describes fragmentation cross sections in high-energy heavy-ion reactions. The new version, EPAX 3, is shown to yield cross sections that are in better agreement with experimental data for the most neutron-rich fragments than the previous version. At the same time, the very good agreement of EPAX 2 with data on the neutron-deficient side has been largely maintained. Comparison with measured cross sections show that the bulk of the data is reproduced within a factor of about 2, for cross sections down to the picobarn range.

The sub-barrier capture reactions ${}^{13,14,15}\mathrm{C}+{}^{232}\mathrm{Th}$, ${}^{4,6}\mathrm{He}+{}^{208,206}\mathrm{Pb}$, ${}^{32}\mathrm{S}+{}^{94,96,98,100}\mathrm{Mo}$, ${}^{100,102,104}$Ru, ${}^{104,106,108,110}$Pd, ${}^{112,116}$Sn, ${}^{36}\mathrm{S}+{}^{92}\mathrm{Mo}$, and ${}^{18}\mathrm{O}+{}^{112,118,124}\mathrm{Sn}$ with light weakly and strongly bound nuclei are studied within the quantum diffusion approach. Based on our analysis a weak influence of halo nuclei on the capture is demonstrated in the reactions mentioned. It is shown that in some cases the neutron transfer with positive $Q$ value can weakly influence or suppress the sub-barrier capture through the change of the deformations of the colliding nuclei. Capture cross sections for the reactions ${}^{13,14,15}\mathrm{C}+{}^{208}\mathrm{Pb}$, ${}^{32,36}\mathrm{S}+{}^{132}\mathrm{Sn}$, and ${}^{40,48}\mathrm{Ca}+{}^{126}\mathrm{Sn}$ are predicted.

Background: The determination of the scattering and reaction amplitudes of hadronic and electromagnetic probes on the single nucleon is of central importance in determining the resonance properties of the nucleon and, in turn, the confining properties of QCD.

Purpose: To achieve in a Chew-Mandelstam parametrization a unified description of single-pion photoproduction data, together with that of pion- and $\eta$-hadroproduction data, which is consistent with unitarity at the two-body level.

Methods: Energy-dependent and single-energy partial-wave analyses of pion photoproduction data have been performed and compared to previous SAID fits and multipoles and to those from the Mainz and Bonn-Gatchina groups.

Results: The new, unified fit is more economical, using fewer parameters, as a result of the consistent implementation of two-body unitarity. Some low-energy structures, not seen by other groups, are no longer present in the current CM12 fit. Additionally, its multipole phases, particularly that of $E_{0+}^{1/2}$, have changed. Photo-decay couplings extracted from CM12 are generally---although not completely---in agreement with an earlier SAID fit (SN11) and the PDG values; significant differences are seen in $N\left(1535\right)S_{11}$ and $N\left(1720\right)P_{13}$.

The symmetry energy effects on the location of the inner edge of neutron star crusts are studied. Three phenomenological models are employed in order to check the accuracy of the well known parabolic approximation of the equation of state for asymmetric nuclear matter in the determination of the transition density $n_t$ and transition pressure $P_t$. The results corroborate the statement that the error due to the assumption that a priori the equation of state is parabolic may introduce a large error in the determination of related properties of a neutron star as the crustal fraction of the moment of inertia and the critical frequency of rotating neutron stars.

Measurements of the $t$-$t$ and $p$-$t$ coincidence events in the ${}^3$H ($\alpha ,tt$)${}^1\text{H}$ reaction have been obtained at incident energy $E_{\alpha }=67.2$ MeV. Various appropriate angular configurations of detectors were chosen in order to observe the population of the ${}^6$He${}^{*}$ state at around 18 MeV. Its contribution appears at the relative energy of $E_{tt}=6.0$ MeV as found from an analysis of the bidimensional spectra. We found the formation of the ${}^6$He excited state at $E^{*}=18.3\pm 0.2$ MeV (with a $\Gamma$ width of 1.1 $\pm$ 0.3 MeV) by using the decay into the $t+t$ binary channel, since the threshold energy of the $t+t$ channel is 12.31 MeV. In each analyzed bidimensional energy spectrum of ($E_t$, $E_t$) and ($E_p$, $E_t$) coincidence events, resonance structures are present due to the formation of both ${}^6$He${}^{*}$ and ${}^4$He${}^{*}$ excited states. Our results on the $E^{*}$ and $\Gamma$ values regarding the ${}^6$He${}^{*}$ level of about 18 MeV are compared with the results obtained using other reactions. Moreover, we also found new $\Gamma$ width values of 0.7 $\pm$ 0.3 and 0.8 $\pm$ 0.4 MeV for the 14.0 $\pm$ 0.4 and 16.1 $\pm$ 0.4 MeV ${}^6$He levels, respectively.

Background: In atomic nuclei, a concentration of electric dipole strength around the particle threshold, commonly denoted as pygmy dipole resonance, may have a significant impact on nuclear structure properties and astrophysical scenarios. A clear identification of these states and the structure of this resonance is still under discussion.

Purpose: We present an experimental and theoretical study of the isospin character of the pygmy dipole resonance and investigation of a splitting of the electric dipole strength previously observed in experiments on $N=82$ nuclei.

Method: The pygmy dipole resonance has been studied in the semi-magic $Z=50$ nucleus ${}^{124}$Sn by means of the $(\alpha ,{\alpha }^{\prime }\gamma )$ coincidence method at $E_{\alpha }=136\mathrm{MeV}$ using the Big-Bite Spectrometer at the Kernfysisch Versneller Instituut in Groningen, The Netherlands.

Results: A splitting of the low-energy part of the electric dipole strength was identified in ${}^{124}$Sn by comparing the differential cross sections measured in $(\alpha ,{\alpha }^{\prime }\gamma )$ to results stemming from $(\gamma ,{\gamma }^{\prime })$ photon-scattering experiments. While an energetically lower-lying group of states is observed in both kinds of experiments, a higher-lying group of states is only excited in the $(\gamma ,{\gamma }^{\prime })$ reaction. In addition, theoretical calculations using the self-consistent relativistic quasiparticle time-blocking approximation and the quasiparticle-phonon model have been performed. Both calculations show a qualitative agreement with the experimental data and predict a low-lying isoscalar component that is dominated by neutron-skin oscillations as expected for the pygmy dipole resonance. Furthermore, the states at higher energies show a pronounced isovector component and a different radial dependence of the corresponding transition densities as expected for the tail of the giant dipole resonance.

Conclusions: An experimental signature of the neutron-skin oscillation of the pygmy dipole resonance has been corroborated. The combination of the presented reactions might make it possible to identify states of this resonance.

The heavy-ion reaction ${}^{22}$Ne+${}^{208}$Pb at 128 MeV beam energy has been studied using the PRISMA-CLARA experimental setup at Legnaro National Laboratories. Elastic, inelastic, and one-nucleon transfer differential cross sections are measured and global agreement is obtained with semiclassical and distorted-wave Born approximation (DWBA) calculations. In particular, the angular distribution of the 2${}^{+}$ state of ${}^{22}$Ne is analyzed by DWBA and a similar calculation is performed for the unstable ${}^{24}$Ne nucleus, using existing data from the reaction ${}^{24}$Ne+${}^{208}$Pb at 182 MeV (measured at SPIRAL with the VAMOS-EXOGAM setup). In both cases the DWBA model gives a good reproduction of the experiment, pointing to a strong reduction of the ${\beta }_2^C$ charge deformation parameter in ${}^{24}$Ne. This follows the trend predicted for the evolution of the quadrupole deformation along the Ne isotopic chain.

The dynamical development of the cooling and hadronizing quark gluon plasma (QGP) is studied in a simple model assuming critical fluctuations in the QGP to hadronic matter and a first-order transition in a small finite system. We consider an earlier determined free-energy density curve in the neighborhood of the critical point, with two local minima corresponding to the equilibrium hadronic and QGP configurations. In this approach the divergence at $e=0$ eliminates fluctuations with negative or zero energy. The barrier between the equilibrium states is obtained from an estimated value of the surface tension between the two phases. We obtain a characteristic behavior for the skewness and the kurtosis of energy density fluctuations, which can be studied via a beam energy scan program.