The Dalitz decay ${\pi }^0\to e^{+}{e}^{-}\gamma$ has been measured with the highest statistical accuracy obtained so far in the $\gamma p\to {\pi }^{0}p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value of the slope parameter for the ${\pi }^0$ electromagnetic transition form factor, $a_{\pi }=0.0315\pm 0.{0026}_{\mathrm{stat}}\pm 0.{0010}_{\mathrm{syst}}$, is obtained from the analysis of $2.4\times {10}^6$ ${\pi }^0\to e^{+}{e}^{-}\gamma$ observed decays. Within experimental uncertainties, it is in agreement with existing measurements and theoretical calculations, with its own uncertainty being smaller than previous results based on the analysis of ${\pi }^0\to e^{+}{e}^{-}\gamma$ decays.

Recently, new quark mass dependent three-nucleon $\left(3N\right)$ forces have been identified, whose contributions in nuclear matter exceed expectations of Weinberg power-counting arguments. In this work, we investigate the impact of the most dominant new interaction term, characterized by the coupling $F_2$, in ab initio calculations of medium-mass nuclei. For this, we combine the new $F_2$ interaction with established $3N$ interactions up to next-to-next-to-leading order $\left({\mathrm{N}}^2\mathrm{LO}\right)$ and next-to-next-to-next-to-leading order $\left({\mathrm{N}}^3\mathrm{LO}\right)$ in chiral effective field theory. We explore two fit strategies for the low-energy couplings. The first is based only on few-body observables, while the second also incorporates information from ${}^{16}\mathrm{O}$. Generally, we find that the $F_2$ interaction has a significant impact on energies and radii, however mainly due to changes in the short-range couplings. Overall, we find no significant systematic improvements in the reproduction of medium-mass nuclei when the additional $F_2$ interaction is included.

Microscopic modeling of low-energy spectroscopy in medium-heavy and heavy odd-$A$ nuclei is an outstanding open problem in nuclear physics. We propose a novel spectra-generating collective model for odd-$A$ nuclei constructed by means of the nuclear energy density functional theory and the interacting boson-fermion model. The bosonic Hamiltonian for an even-even nucleus, which is treated as a core, and the strength parameters for the interactions between the core and an odd nucleon are completely determined by using as microscopic inputs the potential energy curves and deformed single-particle spectra obtained from the self-consistent mean-field calculations. In applications to odd-$A$ Eu, Sm, La, and Ba isotopes, we demonstrate the validity of the proposed method in reproducing reasonably the observed low-energy spectra and shape phase transitions in the general cases of the quadrupole collective states, that is, nearly spherical, strongly deformed, and $\gamma$-soft shapes, in the presence of an odd nucleon in a single-$j$ orbit.

Quantum entanglement provides a unique perspective for probing nuclear structure. In this work, we employ quantum entanglement measures, including proton-neutron entanglement entropy, mutual information, and quantum relative entropy, to investigate the evolution of entanglement patterns as we approach neutron-rich nuclei. The study is carried out in the vicinity of the $N=20$ island of inversion region consisting of even-$A$ Ne, Mg, and Si isotopes, and also for isotones corresponding to $N=20$. The state-of-the-art ab initio valence space in-medium similarity renormalization group method is used for this purpose. We highlight the role of proton-neutron entanglement entropy in the formation of the island of inversion region. Mutual information provides insight into the strength of correlations between proton-proton, neutron-neutron, and proton-neutron single-particle states. While these correlations are relatively weak between protons and neutrons in the ground states, they become comparable to like-particle correlations in excited states. The quantum relative entropy is also studied between $0^{+}$ and $2^{+}$ states of the Ne, Mg, and Si isotopes, as well as $N=20$ isotones, using the Kullback-Leibler divergence and Jensen-Shannon divergence. We perform these calculations by expressing the nuclear wave functions in a Slater-determinant basis and analyzing them through complementary partitions, including proton-neutron and mode-resolved factorizations.

The fusion of $\alpha$ and ${}^8\mathrm{Be}$ to produce a ${}^{12}\mathrm{C}$ nucleus is a crucial process in nucleosynthesis. In the laboratory, this process can only be studied theoretically because a ${}^8\mathrm{Be}$ target or projectile cannot be prepared experimentally. We use the potential scattering theory in the coupled-channel formalism to study such a process in terms of the collision between the $\alpha$ particle on a deformed ${}^8\mathrm{Be}$ nucleus, both on resonance and off resonance in the Hoyle resonance and associated resonances region. The experimental ${}^{12}\mathrm{C}$ energy levels and widths constrain the nuclear potential to suggest the need to include a parity-dependent surface potential component that is more attractive for even-$L$ positive-parity partial waves than for odd-$L$ negative-parity partial waves. As a consequence, the radial dependence of the total potentials for the set of {$0^{+}$, $2^{+}$, $4^{+}$} resonances of ${}^{12}\mathrm{C}$ exhibit a double-hump behavior, possessing two local energy minima and a doublet of each of the ${}^{12}\mathrm{C}$ {$0^{+}$, $2^{+}$, $4^{+}$} resonances in the Hoyle and associated resonances region. We examine the approximate agreement of the theoretical results with experiment and suggest the search for the as-yet unobserved lower-energy $2_2^{+}$ and $4{}_1^{+}$ resonances to test the double-hump potential description. In addition, for practical astrophysical applications, we evaluate and estimate the astrophysical $S\left(E_{\mathrm{c}.\mathrm{m}.}\right)$ factor for the $\alpha +{}^8\mathrm{Be}$ $\to$ ${}^{12}\mathrm{C}\left(0^{+*}\right)$ $\to$ ${}^{12}\mathrm{C}\left(2_1^{+}\right)$ $+$ $\gamma$ reaction for $E_{\mathrm{c}.\mathrm{m}.}$ $<$ 1.0 MeV.

We develop a framework to calculate transport properties in cold, dense relativistic quasiparticle system within the Fermi-liquid theory at the mean-field level. Building on our previous study J. Li et al. [Phys. Rev. C 111, 044904 (2025)], we start from the linearized relativistic Boltzmann equation tailored to quasiparticles with medium-dependent dispersion relation and implement Landau matching conditions, proving that the bulk viscosity is manifestly nonnegative. A low-temperature expansion then yields leading-order $(T/{\mu }^{*})$ expressions for the shear $\left(\eta \right)$ and bulk $\left(\zeta \right)$ viscosities, where the behavior $\zeta /\eta \propto {(T/{\mu }^{*})}^4$ in the degenerate regime is found to be robust against quasiparticle mass correction. We couple the kinetic framework to a Walecka-type mean-field equation of state and compute $\eta$ and $\zeta$ for cold, dense nucleon matter. The transport properties of nucleonic matter in the degenerate regime can be relevant for intermediate beam-energy nuclear experiments.

The quality of recent Short-Range Correlations/Color-Transparency (SRC/CT) Collaboration $J/\psi$ photoproduction data off a ${}^4\mathrm{He}$ target from Hall D at Jefferson Laboratory, combined with the feasibility of measuring the reaction close to the free-nucleon energy threshold, opens the door to using incoherent $J/\psi$ photoproduction to explore a variety of interesting physics aspects. An example is the estimation of the $J/\psi p$ scattering length $|{\alpha }_{J/\psi p}|$ on the bound proton, obtained using the vector meson dominance model. The new experiment E12–25–002, conducted by the SRC/CT Collaboration, was recently approved in Hall D with the GlueX spectrometer, which will significantly enhance the number of reconstructed $J/\psi$ mesons. Using a plane-wave theoretical model to generate quasidata, we estimated that the experiment could achieve a result of $|{\alpha }_{J/\psi p}|=3.08\pm 0.45\mathrm{mfm}$. This value can be compared to an extraction based on the free proton data from the GlueX Collaboration, $|{\alpha }_{J/\psi p}|=3.08\pm 0.55\mathrm{mfm}$. A comparison between the two would provide an opportunity to evaluate the effects of medium modification in light nuclei.

A Bayesian uncertainty quantification analysis of $\alpha$-decay half-life calculations using both the distorted wave Born approximation (DWBA) and Wentzel-Kramers-Brillouin (WKB) methods has been involved in this work. Taking $N=127$ isotones as the examples, I employ Markov chain Monte Carlo sampling to explore the posterior distributions of potential parameters and the spectroscopic factor. This analysis shed light on fundamental differences in the properties of models: DWBA exhibits stronger parameter correlations and multimodal posteriors, reflecting its sensitivity to quantum mechanical constraints, while WKB shows more stable unimodal distributions. Both models achieve comparable accuracy in reproducing experimental half-lives. However, DWBA yields systematically wider 95% credible intervals, providing more conservative uncertainty estimates that reflect the challenges of enforcing strict quantum conditions, whereas WKB produces tighter intervals due to its lower parameter sensitivity. The Bayesian framework thus offers quantitative criteria for model selection based on the degree of alignment between model complexity and the underlying physical scale. This work provides new insights into uncertainty quantification of $\alpha$-decay models and establishes a quantitative criterion based on the alignment between a model's effective degrees of freedom and the physical scale of the probed system. These findings offer practical guidance for future theoretical studies of superheavy nuclei.

Background: The reach of ab initio theory has greatly increased in recent decades. However, predicting the location of the drip lines remains challenging due to uncertainties in nuclear forces and difficulties in describing nuclei that behave as open quantum systems.

Purpose: In this work, we extend the ab initio Gamow density matrix renormalization group (G-DMRG) approach to the regime of broad many-body resonances to pave the way for systematic tests of nuclear forces in light exotic nuclei.

Methods: To stabilize calculations, we introduce a new truncation scheme in the reference space and propose an orbital ordering based on entanglement considerations. We then show how continuum couplings increase entanglement in the many-body problem and propose a new truncation scheme to stabilize the renormalization and accelerate calculations in extreme conditions. Finally, we demonstrate that natural orbitals can be used to efficiently describe broad resonances by introducing a new ordering scheme and by redefining the reference space based on occupations.

Results: Leveraging our findings, we propose a recipe to converge ab initio G-DMRG calculations and apply it in low-lying states of ${}^{5,6}\mathrm{He}$ and ${}^4\mathrm{H}$, demonstrating control of the renormalization and the emergence of convergence patterns. We also obtain the first direct ab initio calculation of the $J^{\pi }={1/2}^{+}$ ground state of ${}^5\mathrm{H}$.

Conclusions: We demonstrate that entanglement due to continuum couplings can be controlled in extreme conditions and successfully extend the G-DMRG approach in the regime of broad many-body resonances.

We propose a novel many-body truncation for Gorkov self-consistent Green's function (SCGF) theory where pairing correlations are handled at first order, while dynamical correlations are described using the particle-number-conserving Dyson-SCGF scheme up to third order in the algebraic diagrammatic construction. The new method is enabled by the introduction of a scheme that allows us to approximate the Gorkov propagator in terms of a particle-number-conserving optimized reference state. The approach provides state-of-the-art predictions of the equation of state and spectral properties of infinite nuclear matter at zero temperature and in the presence of pairing. We find satisfactory results using modern saturating Hamiltonians at next-to-next-to-leading order in chiral effective field theory.

The effect of neutron-proton ($np$) pairing on the high-momentum tail (HMT) of nucleon momentum distributions in symmetric nuclear matter is investigated within a combined framework of the extended Brueckner-Hartree-Fock approach with off-shell BCS theory. The HMT ratio, quantifying the high-momentum fraction in the BCS state relative to the normal state, reaches about 1.06 around the density of $0.052{\mathrm{fm}}^{-3}$, indicating that the maximal contribution of the $np$ pairing amounts to approximately 6% of that from short-range correlations (SRCs). This contribution exhibits a density dependence that closely follows the squared relative pairing gap ${\tilde{\mathrm{\Delta }}}_F=Z_F\mathrm{\Delta }\left(k_F\right)$ with respect to the kinetic energy $E_{k_F}^{*}$ evaluated using the effective mass, suggesting that ${\tilde{\mathrm{\Delta }}}_F^2/E_{k_F}^{*2}$ provides a qualitative measure of the $np$ pairing effect on the HMT. These findings highlight the significant role of $np$ pairing and its interplay with SRCs in shaping nucleon momentum distributions in nuclear matter.

The application of Glauber theory has been playing an increasingly important role with the study of unstable or exotic nuclei. Its adaptation to medium- and high-energy nucleus-nucleus collisions is severely limited because one has to evaluate the matrix elements of multiple-scattering operators. The extraction of physical observables has been done using “approximate” Glauber theory, whose validity is hard to evaluate. We perform a full calculation of the matrix elements using Monte Carlo integration and analyze the elastic differential cross sections and the total reaction cross sections for $p+{}^{12}\mathrm{C}, {}^{4,6}\mathrm{He}+{}^{12}\mathrm{C}$, and ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ collisions. We use the variational Monte Carlo wave functions for ${}^{4,6}\mathrm{He}$ and ${}^{12}\mathrm{C}$ obtained by using realistic two- and three-nucleon potentials. We demonstrate the performance of the Glauber-theory calculations by comparing with available experimental data. We further discuss the accuracy of the conventional approximate methods in light of the cumulant expansion for Glauber's phase-shift function.

We obtain an empirical relation for the neutron star maximum mass arising from a particular combination of the saturation density ($n_0$), the effective mass ($m^{*}$), and (when present) the vector meson self-coupling constant ($\zeta$) within the relativistic mean-field model framework. Observations of massive neutron stars heavier than $\approx 2M_{\odot }$ have eliminated the softest equation of state from consideration and impose strong constraints on nuclear interactions used to model dense nuclear matter. To date, numerous efforts have been made to refine relativistic mean-field models through the inclusion of additional mesons, such as the $\delta$ meson, as well as through the introduction of additional couplings. We show that current relativistic mean field models, including our own constructions, exhibit a maximum neutron star mass that is primarily determined by the combination of the saturation density, the effective mass at saturation, and the vector meson self-coupling constant. When constraining the pure neutron matter equation of state using chiral effective field theory (ChEFT) at low densities, 250 parameter sets were generated to derive an empirical formula for the maximum mass of neutron stars and apply the formula with the present relativistic mean field models.

We combine the three-dimensional (3D) two-potential approach (3DTPA) with the physics-informed neural network (PINN) to compute the $\alpha$ decay width of deformed nuclei, which is expressed in terms of the 3D bound-state wave function and the Coulomb scattering wave function on the separation surface of 3DTPA. The designed PINN output representation and loss function enable stable and accurate solutions of 3D bound-state wave function whose amplitude is extremely small on the separation surface. The PINN is validated against the exact solutions of anisotropic harmonic-oscillator potential and the widely used Woods-Saxon potential. With a microscopic potential constructed by the quartetting wave-function approach (QWFA), the $\alpha$-cluster preformation and tunneling probabilities of typical deformed $\alpha$ emitters ${}^{256}\mathrm{No}$ and ${}^{274}\mathrm{Ds}$ are self-consistently computed by using the $3\text{DTPA}+\text{PINN}$ method. It is found that the method provides a practical tool for microscopic studies of quasistationary states of deformed $\alpha$ emitters.

A systematic investigation of the high-spin band structures observed in ${}^{103,105,107,109}\mathrm{Nb}$ and ${}^{103,105,107,109}\mathrm{Tc}$ nuclides is performed using the triaxial projected shell model approach. For ${}^{103,105}\mathrm{Nb}$ isotopes, four bands have been populated with the lowest three bands corresponding to yrast, $\gamma$, and $2\gamma$ bands. The nature of the fourth observed band has remained unresolved as it has been shown from the transition intensity ratios that this band cannot correspond to the expected $3\gamma$ band. It is demonstrated in the present work that this fourth band is the second $\gamma$ band, resulting from the combination, $K=K_0-2$ with $K_0$ being the “$K$” value of the ground state configuration. The excitation energy and other properties of this band structure are predicted for all the studied nuclides.

We develop a self-consistent relativistic second random-phase approximation (RSRPA) based on a covariant energy density functional with density-dependent point-coupling interaction. The formalism extends the conventional simple configuration space composed of particle-hole transitions by including two-particle–two-hole (2p-2h) configurations through a generalized Thouless ansatz and a time-dependent variational principle. To ensure consistency with the underlying mean-field ground state and avoid the double counting of correlations, we implement the subtraction method, in which the static contribution is removed from the residual interaction. The first applications of the RSRPA include studies of isoscalar and isovector giant monopole (ISGMR and IVGMR) and quadrupole resonances (ISGQR and IVGQR) in ${}^{16}\mathrm{O}$, which demonstrate the importance of 2p-2h couplings to describe the fragmentation of the transition strength and the stabilizing role of the subtraction method.

Complete isotopic fission yields distributions of ${}^{240}\mathrm{Pu}$ have been measured as a function of the initial excitation energy. The ${}^{240}\mathrm{Pu}$ fissioning system was produced through a two-proton transfer reaction between a ${}^{238}\mathrm{U}$ beam and a ${}^{12}\mathrm{C}$ target. The reaction was measured in inverse kinematics at Coulomb barrier energies, allowing for the full distribution of fission fragments to be isotopically identified with the $\mathrm{VAMOS}++$ Spectrometer. The excitation energy of the system was measured on an event-by-event basis by detecting the targetlike recoil ${}^{10}\mathrm{Be}$ in a segmented silicon telescope. This manuscript reports on the evolution of the fission yields as a function of the excitation energy of the system between 8.2 to 11.9 MeV. The influence of the excitation energy is manifested in the damping of shell effects that feed the yields in the symmetry valley, as well as in a reduction of the neutron content of the fragments. This reduction, however, is observed only in the heavy fragment, while the neutron content of the light fragment remains unaffected. The comparison with previous measurements, models, and evaluations highlights the importance of correlated observables for improving fission models.

Background: Dynamical effects associated with the fusion of mass-symmetric systems remain a central topic of research in nuclear reaction studies. Over the past few decades, measurements of light-particle evaporation spectra and their deviations from standard statistical model predictions have been extensively employed to investigate these effects. Such indirect probes have indicated the presence of fusion hindrance, attributed to the non-fusion of higher angular momentum ($l$) states in fusion of symmetric systems. Further, more recent investigations have suggested that similar effects may also manifest in asymmetric systems particularly at higher values of excitation energies. Since the suppression of fusion at higher angular momenta suggests a corresponding reduction in the fusion cross sections for such systems, the measurement of fusion cross sections or spin distributions would give better insight into the possible fusion hindrance. However, such anomalies have not yet been explored using these probes.

Purpose: Fusion cross sections have been used as a probe to investigate the influence of entrance-channel mass asymmetry on fusion dynamics, as well as to examine the possible suppression of fusion for higher angular momentum and the deviations of light-particle evaporation spectra from the standard statistical model predictions.

Method: Evaporation-residue (ER) excitation function measurements have been carried out for the reactions ${}^{16}\mathrm{O}+{}^{64}\mathrm{Zn}$ and ${}^{32}\mathrm{S}+{}^{48}\mathrm{Ti}$, both leading to the formation of the ${}^{80}\mathrm{Sr}$ compound nucleus. The experiments were performed using the Heavy Ion Reaction Analyzer spectrometer. The experimentally obtained fusion cross sections were compared with each other as well as with the predictions from time-dependent Hartree-Fock (TDHF) calculations. Furthermore, the measured fusion cross sections have been employed to interpret the light-particle evaporation spectra for these systems, as reported in the literature.

Results: The experimentally obtained fusion cross sections for both systems show good agreement with each other on a reduced scale, and the measured data are reasonably well reproduced by TDHF calculations. The present investigation rules out the possibility of non-fusion of higher angular momentum ($l$) states in symmetric systems, contrary to earlier reports in the literature. However, the fusion timescales extracted from the TDHF calculations indicate a delay in the fusion process for both symmetric and asymmetric systems, suggesting the presence of dynamical effects.

Conclusions: The measured ER cross sections in the spanned energy region are insensitive to dynamical effects. However, the delay in the fusion timescales as predicted by TDHF calculations indicates a possible existence of fusion hindrance. To explore the fusion hindrance for such systems, it may be important to measure the spin distribution of the populated compound nucleus at high excitation energies.