The aim of the present study is to calculate the nuclear distribution associated at finite temperature to any given equation of state of stellar matter based on the Wigner-Seitz approximation, for direct applications in core-collapse simulations. The Gibbs free energy of the different configurations is explicitly calculated, with special care devoted to the calculation of rearrangement terms, ensuring thermodynamic consistency. The formalism is illustrated with two different applications. First, we work out the nuclear statistical equilibrium cluster distribution for the Lattimer and Swesty equation of state, widely employed in supernova simulations. Secondly, we explore the effect of including shell structure, and consider realistic nuclear mass tables from the Brussels-Montreal Hartree-Fock-Bogoliubov model (specifically, HFB-24). We show that the whole collapse trajectory is dominated by magic nuclei, with extremely spread and even bimodal distributions of the cluster probability around magic numbers, demonstrating the importance of cluster distributions with realistic mass models in core-collapse simulations. Simple analytical expressions are given, allowing further applications of the method to any relativistic or nonrelativistic subsaturation equation of state.

To describe obvious intruder states and nonzero quadrupole moments of $\gamma$-soft nuclei such as ${}^{194}\mathrm{Pt}$, a rotor extension plus intruder configuration mixing with $2n$-particle and $2n$-hole configurations from $n=0$ up to $n\to \infty$ in the O(6) ($\gamma$-unstable) limit of the interacting boson model is proposed. It is shown that the configuration mixing scheme keeps the lower part of the $\gamma$-unstable spectrum unchanged and generates the intruder states due to the mixing. It is further shown that almost all low-lying levels below 2.17 MeV in ${}^{194}\mathrm{Pt}$ can be well described by modifying the O(6) quadrupole-quadrupole interaction into an exponential form. The third-order term needed for a rotor realization in the interacting boson model seems necessary to produce nonzero quadrupole moments with the correct sign.

Delayed $\gamma$-ray and conversion-electron spectroscopy is performed on $A=152$ fission fragments, at the Lohengrin spectrometer of the Institut Laue-Langevin, providing a new decay scheme for ${}^{152}\mathrm{Pr}$. The quasiparticle phonon model, combined with the particle-rotor model, which allows octupole correlations and Coriolis mixing to be taken into account, is applied to analyze its low-energy structure. The main configurations are found to be $(\pi 3/2\left[422\right]\otimes \nu 5/2\left[642\right])1^{+}$ for the isomer and $(\pi 3/2\left[541\right]\otimes \nu 3/2\left[521\right])3^{+}$ for the ground state.

Ab initio methods aim to solve the nuclear many-body problem with controlled approximations. Virtually exact numerical solutions for realistic interactions can only be obtained for certain special cases such as few-nucleon systems. Here we extend the reach of exact diagonalization methods to handle model spaces with dimension exceeding ${10}^{10}$ on a single compute node. This allows us to perform no-core shell model (NCSM) calculations for ${}^6\mathrm{Li}$ in model spaces up to $N_{\max }=22$ and to reveal the ${}^4\mathrm{He}$+d halo structure of this nucleus. Still, the use of a finite harmonic-oscillator basis implies truncations in both infrared (IR) and ultraviolet (UV) length scales. These truncations impose finite-size corrections on observables computed in this basis. We perform IR extrapolations of energies and radii computed in the NCSM and with the coupled-cluster method at several fixed UV cutoffs. It is shown that this strategy enables information gain also from data that is not fully UV converged. IR extrapolations improve the accuracy of relevant bound-state observables for a range of UV cutoffs, thus making them profitable tools. We relate the momentum scale that governs the exponential IR convergence to the threshold energy for the first open decay channel. Using large-scale NCSM calculations we numerically verify this small-momentum scale of finite nuclei.

Early measurements at the BNL Relativistic Heavy Ion Collider (RHIC) demonstrated jet quenching through the suppression of pairs of high momentum hadrons. These dihadron correlations have a large correlated background. As understanding of the background improved, it was recognized in the field that a significant term was omitted from the background and several dihadron correlation results were quantitatively and qualitatively incorrect. The original measurements demonstrating jet quenching have not been revisited. These measurements are repeated in this paper in a kinematic range similar to the original measurement using publicly available data, applying current knowledge about the background. The new results are qualitatively consistent with the previous results, demonstrating complete suppression of the away side within uncertainties.

We discuss the adequate treatment of the three- and four-body dynamics for the quark model picture of double-charm baryons and tetraquarks. We stress that the variational and Born-Oppenheimer approximations give energies very close to the exact ones, while the diquark approximation might be somewhat misleading. The Hall-Post inequalities also provide very useful lower bounds that exclude the possibility of stable tetraquarks for some mass ratios and some color wave functions.

Scaling features of the nuclear electromagnetic response functions unveil aspects of nuclear dynamics that are crucial for interpreting neutrino- and electron-scattering data. In the large momentum-transfer regime, the nucleon-density response function defines a universal scaling function, which is independent of the nature of the probe. In this work, we analyze the nucleon-density response function of ${}^{12}\mathrm{C}$, neglecting collective excitations. We employ particle and hole spectral functions obtained within two distinct many-body methods, both widely used to describe electroweak reactions in nuclei. We show that the two approaches provide compatible nucleon-density scaling functions that for large momentum transfers satisfy first-kind scaling. Both methods yield scaling functions characterized by an asymmetric shape, although less pronounced than that of experimental scaling functions. This asymmetry, only mildly affected by final state interactions, is mostly due to nucleon-nucleon correlations, encoded in the continuum component of the hole spectral function.

Cross sections of proton capture reactions on ${}^{74}\mathrm{Se}$, ${}^{78}\mathrm{Se}$, and ${}^{80}\mathrm{Se}$ have been measured at incident beam energies from 2 to 6 MeV, 1.7 to 3 MeV, and 1.5 to 3.5 MeV, respectively. In the case of ${}^{78,80}\mathrm{Se}$, cross sections were obtained from in-beam $\gamma$-angular distribution measurements, whereas for the ${}^{74}\mathrm{Se}$ isotope they were derived from off-beam activity measurements. The measured cross sections were compared with calculations performed with the nuclear reaction code talys (version 1.6). A good agreement between theory and experiment was found. Astrophysical $S$ factors and reaction rates deduced from the experimental and calculated cross sections were also compared and the impact of different nuclear ingredients in the calculations on the reaction rates was investigated. It was found that, for certain combinations of nuclear input models, the reaction rates obtained at temperatures relevant to $p$-process nucleosynthesis differ by a factor 2 at the most, differences that are well within the acceptable deviations of calculated $p$-nuclei abundances and observations.

A systematic analysis of the antimagnetic rotation band using $r$-helicity formalism is carried out for the first time. The observed octupole correlation in a nucleus is likely to play a role in establishing the antimagnetic spectrum. Such octupole correlations are explained within the helical orbits. In a rotating field, two identical fermions (generally protons) with paired spins generate these helical orbits in such a way that its positive (i.e., up) spin along the axis of quantization refers to one helicity (right-handedness) while negative (down) spin along the same quantization-axis decides another helicity (left-handedness). Since the helicity remains invariant under rotation, therefore, the quantum state of a fermion is represented by definite angular momentum and helicity. These helicity represented states support a pear-shaped structure of a rotating system having $z$ axis as the symmetry axis. A combined operation of parity, time-reversal, and signature symmetries ensures an absence of one of the signature partner band from the observed antimagnetic spectrum. This formalism has also been tested for the recently observed negative parity $\mathrm{\Delta }I=2$ antimagnetic spectrum in odd-$A$ ${}^{101}\mathrm{Pd}$ nucleus and explains nicely its energy spectrum as well as the $B\left(E2\right)$ values. Further, this formalism is found to be fully consistent with twin-shears mechanism popularly known for such type of rotational bands. It also provides significant clue for extending these experiments in various mass regions spread over the nuclear chart.

The angular distribution of individual $\gamma$ rays, emitted from a neutron-induced compound-nuclear state via radiative capture reaction of ${}^{139}\mathrm{La}(n,\gamma )$ has been studied as a function of incident neutron energy in the epithermal region by using germanium detectors. An asymmetry $A_{\mathrm{LH}}$ was defined as $(N_{\mathrm{L}}-N_{\mathrm{H}})/(N_{\mathrm{L}}+N_{\mathrm{H}})$, where $N_{\mathrm{L}}$ and $N_{\mathrm{H}}$ are integrals of low- and high-energy region of a neutron resonance respectively, and we found that $A_{\mathrm{LH}}$ has the angular dependence of $(Acos{\theta }_{\gamma }+B)$, where ${\theta }_{\gamma }$ is the emitted angle of $\gamma$ rays, with $A=-0.3881\pm 0.0236$ and $B=-0.0747\pm 0.0105$ in 0.74 eV $p$-wave resonance. This angular distribution was analyzed within the framework of interference between $s$- and $p$-wave amplitudes in the entrance channel to the compound-nuclear state, and it is interpreted as the value of the partial $p$-wave neutron width corresponding to the total angular momentum of the incident neutron combined with the weak matrix element, in the context of the mechanism of enhanced parity-violating effects. Additionally, we use the result to quantify the possible enhancement of the breaking of time-reversal invariance in the vicinity of the $p$-wave resonance.

The differential cross sections and decay angular distributions for coherent $\varphi$-meson photoproduction from helium-4 are measured for the first time at forward angles with linearly polarized photons in the energy range $E_{\gamma }=1.685–2.385\text{GeV}$. Thanks to the target with spin-parity $J^P=0^{+}$, unnatural-parity exchanges are absent, and thus natural-parity exchanges can be investigated clearly. The decay asymmetry with respect to photon polarization is shown to be very close to the maximal value. This ensures the strong dominance ($>94$%) of natural-parity exchanges in this reaction. To evaluate the contribution from natural-parity exchanges to the forward cross section ($\theta =0^{\circ }$) for the $\gamma p\to \varphi p$ reaction near threshold, the energy dependence of the forward cross section ($\theta =0^{\circ }$) for the $\gamma {}^4\mathrm{He}\to \varphi {}^4\mathrm{He}$ reaction is analyzed. The comparison to $\gamma p\to \varphi p$ data suggests that enhancement of the forward cross section arising from natural-parity exchanges and/or destructive interference between natural-parity and unnatural-parity exchanges is needed in the $\gamma p\to \varphi p$ reaction near threshold.

We consider electron-deuteron deep-inelastic scattering (DIS) with detection of a proton in the nuclear fragmentation region (“spectator tagging”) as a method for extracting the free neutron structure functions and studying their nuclear modifications. Such measurements could be performed at a future electron-ion collider (EIC) with suitable forward detectors. The measured proton recoil momentum ($\lesssim 100$ MeV in the deuteron rest frame) specifies the deuteron configuration during the high-energy process and permits a controlled theoretical treatment of nuclear effects. Nuclear and nucleonic structure are separated using methods of light-front quantum mechanics. The impulse approximation to the tagged DIS cross section contains the free neutron pole, which can be reached by on-shell extrapolation in the recoil momentum. Final-state interactions (FSIs) distort the recoil momentum distribution away from the pole. In the intermediate-$x$ region $0.1<x<0.5$ FSIs arise predominantly from interactions of the spectator proton with slow hadrons produced in the DIS process on the neutron (rest frame momenta $\lesssim 1\mathrm{GeV}$, target fragmentation region). We construct a schematic model describing this effect, using final-state hadron distributions measured in nucleon DIS experiments and low-energy hadron scattering amplitudes. We investigate the magnitude of FSIs, their dependence on the recoil momentum (angular dependence, forward/backward regions), their analytic properties, and their effect on the on-shell extrapolation. We comment on the prospects for neutron structure extraction in tagged DIS with an EIC. We discuss possible extensions of the FSI model to other kinematic regions (large/small $x$). In tagged DIS at $x\ll 0.1$ FSIs resulting from diffractive scattering on the nucleons become important and require separate treatment.

The influence of resonance decay dynamics on the momentum spectra of pions in heavy-ion collisions is examined. Taking the decay processes $\omega \to 3\pi$ and $\rho \to 2\pi$ as examples, I demonstrate how the resonance width and details of decay dynamics (via the decay matrix element) can modify the physical observables. The latter effect is commonly neglected in statistical models. To remedy the situation, a theoretical framework for incorporating hadron dynamics into the analysis is formulated, which can be straightforwardly extended to describe general $N$-body decays.

We study the effects of free space nucleon radius on nuclear matter and neutron stars within the framework of the quark mean field model. The nucleon radius is treated self-consistently with this model, where quark confinement is adjusted to fit different values of nucleon radius. Corrections due to center-of-mass motion, quark-pion coupling, and one gluon exchange are included to obtain the nucleon mass in vacuum. The meson coupling constants that describe the behavior of the many-body nucleonic system are constructed by reproducing the empirical saturation properties of nuclear matter, including the recent determinations of symmetry energy parameters. Our results show that the nucleon radius in free space has negligible effects on the nuclear matter equation of state and neutron star mass-radius relations, which is different from the conclusion drawn in previous studies. We further explore that the sensitivity of star radius on the nucleon radius found in earlier publications is actually from the symmetry energy and its slope.

We computed a new set of static fission properties suited for $r$-process calculations. The potential energy surfaces and collective inertias of 3640 nuclei in the superheavy region are obtained from self-consistent mean-field calculations using the Barcelona-Catania-Paris-Madrid energy density functional. The fission path is computed as a function of the quadrupole moment by minimizing the potential energy and exploring octupole and hexadecapole deformations. The spontaneous fission lifetimes are evaluated employing different schemes for the collective inertias and vibrational energy corrections. This allows us to explore the sensitivity of the lifetimes to those quantities together with the collective ground-state energy along the superheavy landscape. We computed neutron-induced stellar reaction rates relevant for $r$-process nucleosynthesis using the Hauser-Feshbach statistical approach and study the impact of collective inertias. The competition between different reaction channels including neutron-induced rates, spontaneous fission, and $\alpha$ decay is discussed for typical $r$-process conditions.

$0s$-orbit $\mathrm{\Lambda }$ states in $p$-shell double-$\mathrm{\Lambda }$ hypernuclei (${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{A}Z$), ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^8\mathrm{Li}$, ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^9\mathrm{Li}$, ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{10,11,12}\mathrm{Be}$, ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{12,13}\mathrm{B}$, and ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{14}\mathrm{C}$ are investigated. Microscopic cluster models are applied to core nuclear part and a potential model is adopted for $\mathrm{\Lambda }$ particles. The $\mathrm{\Lambda }$-core potential is a folding potential obtained with effective $G$-matrix $\mathrm{\Lambda }\text{−}N$ interactions, which reasonably reproduce energy spectra of ${}_{\mathrm{\Lambda }}{}^{A-1}Z$. System dependence of the $\mathrm{\Lambda }\text{−}\mathrm{\Lambda }$ binding energies is understood by the core polarization energy from nuclear size reduction. Reductions of nuclear sizes and $E2$ transition strengths by $\mathrm{\Lambda }$ particles are also discussed.

Background: The nuclear optical potential is a successful tool for the study of nucleon-nucleus elastic scattering and its use has been further extended to inelastic scattering and other nuclear reactions. The nuclear density of the target nucleus is a fundamental ingredient in the construction of the optical potential and thus plays an important role in the description of the scattering process.

Purpose: In this paper we derive a microscopic optical potential for intermediate energies using ab initio translationally invariant nonlocal one-body nuclear densities computed within the no-core shell model (NCSM) approach utilizing two- and three-nucleon chiral interactions as the only input.

Methods: The optical potential is derived at first order within the spectator expansion of the nonrelativistic multiple scattering theory by adopting the impulse approximation. Nonlocal nuclear densities are derived from the NCSM one-body densities calculated in the second quantization. The translational invariance is generated by exactly removing the spurious center-of-mass (COM) component from the NCSM eigenstates.

Results: The ground-state local and nonlocal densities of ${}^{4,6,8}\mathrm{He}$, ${}^{12}\mathrm{C}$, and ${}^{16}\mathrm{O}$ are calculated and applied to optical potential construction. The differential cross sections and the analyzing powers for the elastic proton scattering off these nuclei are then calculated for different values of the incident proton energy. The impact of nonlocality and the COM removal is discussed.

Conclusions: The use of nonlocal densities has a substantial impact on the differential cross sections and improves agreement with experiment in comparison to results generated with the local densities especially for light nuclei. For the halo nuclei ${}^6\mathrm{He}$ and ${}^8\mathrm{He}$, the results for the differential cross section are in a reasonable agreement with the data although a more sophisticated model for the optical potential is required to properly describe the analyzing powers.

Within the isospin- and momentum-dependent transport model IBUU11, we examine the relativistic retardation effects of electrical fields on the ${\pi }^{-}/{\pi }^{+}$ ratio and neutron-proton differential transverse flow in heavy-ion collisions at intermediate energies. Compared to the static Coulomb fields, the retarded electric fields of fast-moving charges are known to be anisotropic and the associated relativistic corrections can be significant. They are found to increase the number of energetic protons in the participant region at the maximum compression by as much as 25% but that of energetic neutrons by less than 10% in ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ reactions at a beam energy of 400 MeV/nucleon. Consequently, more ${\pi }^{+}$ and relatively fewer ${\pi }^{-}$ mesons are produced, leading to an appreciable reduction of the ${\pi }^{-}/{\pi }^{+}$ ratio compared to calculations with the static Coulomb fields. Also, the neutron-proton differential transverse flow, as another sensitive probe of high-density symmetry energy, is also decreased appreciably due to the stronger retarded electrical fields in directions perpendicular to the velocities of fast-moving charges compared to calculations using the isotropic static electrical fields. Moreover, the retardation effects on these observables are found to be approximately independent of the reaction impact parameter.