Gravitational-wave observations have renewed interest in the black-hole mass gap and in the maximum mass of first-generation black holes below its lower edge. The ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ reaction plays a central role in this problem because it determines the carbon-to-oxygen ratio after core-helium burning and thereby affects the later evolution of massive stars toward pulsational pair instability and pair-instability supernovae. Recent attempts to constrain $S\left(300\mathrm{keV}\right)$ from gravitational-wave population inferences face important limitations, because the lower edge of the black-hole mass gap is not directly measured. It is inferred model dependently from assumptions about stellar evolution, metallicity, mass loss, rotation, binary evolution, hierarchical mergers, selection effects, priors, and the adopted population model. Therefore, values of $S\left(300\mathrm{keV}\right)$ inferred from black-hole populations must remain consistent with independent nuclear-physics constraints. In this work the low-energy ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O} S$ factor is reanalyzed using updated information on the subthreshold $1^{-}$ and $2^{+}$ asymptotic normalization coefficients (ANCs) and on the ground-state ANC of ${}^{16}\mathrm{O}$, together with direct capture data. These constraints favor a lower $S\left(300\mathrm{keV}\right)$ than the older central evaluation and disfavor very large values required by some black-hole-population interpretations. Combining the resulting ANC-constrained $S\left(300\mathrm{keV}\right)$ range with the transformed relation between this quantity and the lower edge of the pair-instability mass gap gives $\frac{M_{\mathrm{BH}}}{M_{\odot }}\simeq 61-75$. Thus, the present nuclear-physics constraints favor a relatively high lower edge of the first-generation black-hole mass gap.

We employ the three-body model to the ${}^{12}\mathrm{Be}$ nucleus by solving the Faddeev equations in momentum space using the partial-wave decomposition method. Four sets of interactions between the ${}^{10}\mathrm{Be}$ core and the neutron, $V_{cn}$, are constructed in different ways to test the validity of the three-body model. The spectra of ${}^{12}\mathrm{Be}$ are obtained, including the $0_1^{+}, 2^{+}, 1^{-}, 0^{-}$, and $0_3^{+}$ states, together with the rms radii, $R_m$. Our results are consistent with previous three-body computations of ${}^{12}\mathrm{Be}$ in coordinate space and the most recent ab initio calculations. For the $0_1^{+}$ ground state, the energies and radii of four sets of $V_{cn}$ are close to the experimental data. In particular, when $V_{cn}$ is constructed close to the realistic core-neutron interaction, the resulting probabilities of the $p$-wave configurations are similar to those obtained from earlier shell-model calculations. Additionally, we predict two excited states, $0^{-}$ and $0_3^{+}$, together with their two-neutron separation energies. For the first excited $2^{+}$ state, our calculations suggest that, if the $d_{3/2}$ and $d_{5/2}$ orbitals share the 1.28 MeV resonance state in ${}^{11}\mathrm{Be}$, then the three-body model could produce results that align with the experimental data.

We theoretically investigate a quartet superfluid state in fermionic matter by using the quartet Bardeen-Cooper-Schrieffer (BCS) variational theory and the Green's function method. We demonstrate that the quartet BCS theory with the multiple-infinite-product ansatz successfully reproduces an exact four-body result in a one-dimensional four-component Fermi gas at the dilute limit, in contrast to the single-infinite-product ansatz. To see the validity of the quartet BCS state, we derive the self-consistent equation for the quartet superfluid order parameter within the generalized imaginary-time Nambu-Gor'kov formalism, which is found to be consistent with the quartet BCS variational equation. Moreover, by numerically computing the momentum-resolved single-particle spectral function in a one-dimensional system, we discuss how the single-particle spectra evolve with increasing the strength of the four-body cluster formation. We show that a coherent BCS-like quasiparticle branch on the weak-coupling side evolves into a strongly damped, continuum-dominated spectrum in the strong-coupling side, while nonzero quartet superfluid order parameter persists throughout the crossover regime. Our results would be useful for understanding beyond-BCS pairing effects and four-body cluster formations in fermionic systems in an interdisciplinary way.

To study the isoscalar giant resonances in a deformed case, background-free $\alpha$-particle inelastic scattering measurements using a 386 MeV $\alpha$ beam were performed on the highly deformed ${}^{172}\mathrm{Yb}$ nucleus using the Grand Raiden spectrometer at the Research Center for Nuclear Physics (RCNP) at very forward angles, including $0^{\circ }$. The strength distributions for the isoscalar giant resonances up to $L\le 3$ were obtained using multipole decomposition analysis. The isoscalar giant monopole resonance (ISGMR) strength exhibits a splitting into two components, interpreted as the coupling of the ISGMR with the $K=0$ component of the isoscalar giant quadrupole resonance (ISGQR). A bimodal structure is observed in the strength distribution of the isoscalar giant dipole resonance. The ISGQR strength shows an enhancement near 25 MeV, attributed to the excitation of an overtone mode, while the broadening of the main-tone peak is associated with nuclear deformation. The experimental results are compared with theoretical strength distributions calculated using the quasiparticle finite amplitude method for $L\le 3$.

We develop a generalized finite-temperature proton-neutron BCS framework using the superoperator formalism, incorporating both isovector and isoscalar monopole pairing channels. Numerical calculations for a schematic equidistant multilevel model and realistic even-even Ge isotopes demonstrate the emergence of proton-neutron ($pn$) pairing reentrance in even-even asymmetric ($N>Z$) nuclei with preexisting like-nucleon pairing correlations. This nonmonotonic behavior arises from thermal excitations that partially lift Pauli blocking of single-particle orbitals near the chemical potentials, thereby enlarging the phase space for $pn$ pair formation. We uncover a delicate interplay between thermal unblocking and like-nucleon pairing, which can either suppress or enhance $pn$ correlations depending on temperature and shell filling. A qualitative analysis of Fermi charge-exchange strength functions in hot ${}^{72}\mathrm{Ge}$, which neglects the residual interaction between thermal quasiparticles, suggests that $pn$ pairing reentrance may alter the transition strength distribution around $T\approx 1$ MeV. This indicates that finite-temperature $pn$ correlations could potentially impact stellar weak-interaction rates in $rp$-process and supernova environments.

The excitation energy difference between terminating states based on the $f_{7/2}^n$ and $d_{3/2}^{-1}{f}_{7/2}^{n+1}$ configurations has been studied within the cranked relativistic mean field framework. The discrepancy between the experimental data and the theoretical predictions is found to decrease systematically with increasing asymmetry, indicating an improved description of neutron-rich nuclei. By constraining the relevant shell gap and refitting the relativistic mean field parameter set, a new parametrization is obtained that significantly improves the description of single-particle energies near the shell gap without compromising the reproduction of bulk nuclear properties.

In this work, a comprehensive, two-photon-exchange (TPE)-consistent analysis of the unpolarized reduced cross section ${\sigma }_R(\varepsilon ,Q^2)$ for elastic electron-proton ($ep$) scattering is performed to search for possible contributions from a light neutral scalar mediator and to establish quantitative constraints in their absence. The framework incorporates the standard one-photon-exchange (OPE) term, the phenomenological TPE correction, and an additional scalar amplitude whose strength is governed by the dimensionless coupling ratio $\beta ={\alpha }_s/\alpha$, defined as the scalar proton-electron coupling ${\alpha }_s$ normalized to the electromagnetic fine-structure constant $\alpha$. The scalar strength $S\left(Q^2\right)$ is extracted from linear Rosenbluth fits to world ${\sigma }_R$ data at 134 $Q^2$ points spanning $0.0155\le Q^2\le 5.5{\mathrm{GeV}}^2$. The data exhibit no statistically significant deviation from the $\mathrm{OPE}+\mathrm{TPE}$ baseline, and the global profile likelihood saturates the physical boundary $\widehat{\beta }=0$ for all scanned mediator masses. One-sided 95% confidence-level upper limits ${\beta }_{95}\left(m_s\right)$ are obtained using a profile-likelihood construction over the mass range $0.04\le m_s\le 10\mathrm{GeV}$. Accordingly, the primary result of this work is the determination of quantitative exclusion limits on the scalar coupling, rather than evidence of a nonzero contribution. The resulting exclusion curve lies at the level of a few $\times {10}^{-3}$ to ${10}^{-2}$ depending on $m_s$, with systematic uncertainties increasing the limits by only 5–10% across most of the mass range. These limits improve upon, or are comparable to, previously reported electromagnetic-form-factor-based scalar constraints in the low- to intermediate-mass region and constitute the first dedicated, TPE-consistent ${\sigma }_R$-based search for light scalar exchange in elastic $ep$ scattering. No evidence for a scalar contribution is observed within the present experimental sensitivity.

The impact of Coulomb core polarization on the neutron density distribution of ${}^{48}\mathrm{Ca}$ is investigated. The Coulomb boundary radius is located before the neutron skin region, leading to proton admixture and establishing neutron skin impurity as an intrinsic feature of the density profile. Using the ${(}^3\mathrm{He},t)$ isobaric analog state (IAS) reaction at 420 MeV, the impurity-induced modification of the probed neutron distribution is quantified. For a neutron skin of 0.144 fm, consistent with the CREX thin-skin scenario, Coulomb core polarization enhances the probed neutron distribution by approximately 0.052 fm. This value is remarkably close to the difference between the CREX and RCNP neutron skin determinations, providing a physical mechanism to reconcile the discrepancy between electroweak and hadronic probes in ${}^{48}\mathrm{Ca}$. These findings provide new insights into the CREX-PREX puzzle, highlight the importance of accounting for Coulomb core polarization in neutron distribution analyses, and motivate future IAS charge-exchange measurements as a complementary hadronic probe.

The halo nucleon-core system is, by definition, a shallow state nucleus. The nucleon, in most cases a neutron, is loosely bound to the other nucleons forming the core. Accordingly, the system is located inside the universal window; the halo nucleon most likely resides far from the rest of the nucleons, showing a remarkable insensitivity to details of the interaction with the core. The system can be described using a simple nucleon-core interaction, and this description can be extended to the nucleon-nucleon-core system. Specifically, treating the neutron-core and the neutron-neutron-core systems with a Gaussian interaction as a reference, we show trajectories inside the universal window governed by interaction parameters determined from low-energy observables, such as the neutron-core binding energy, scattering length, and effective range. In this way, we can relate properties of different halo nuclei that might seem uncorrelated. In particular, we determine the three-body parameter, the binding momentum at the unitary limit, and show that the two-neutron halo nuclei emerge from that limit following a linear trajectory depending on the neutron-core range.

Short-range correlated (SRC) nucleon pairs provide a sensitive probe of the short-distance structure of atomic nuclei and the underlying nucleon-nucleon (NN) interaction. We present a simple numerical method to estimate the number of two- and three-nucleon SRC clusters using an independent-particle shell model with a harmonic-oscillator basis. The relative abundances of proton-neutron (pn), proton-proton (pp), and neutron-neutron (nn) SRC pairs are calculated for Al, Fe, and Pb nuclei, normalized to carbon, and compared with existing analytical predictions and available extractions from experimental data. We extend the analysis to the isotopes ${}^{40}\mathrm{Ca}, {}^{48}\mathrm{Ca}$, and ${}^{54}\mathrm{Fe}$ (collectively, the CaFe nuclei), which have been recently studied experimentally. These isotopes provide insight into the role of $1f_{7/2}$ shell occupancy in SRC-pair formation. Finally, we present a reference baseline for three-nucleon (3N) SRC cluster abundances across the studied nuclei, assuming 3N clusters originate from independent two-nucleon (2N) interactions. The predicted baseline is about 3.5% 3N-SRC/2N-SRC ratio for all medium and heavy nuclei. Deviations from this baseline may indicate the presence of additional short-range nuclear dynamics.

We examined the ratios of neutron and proton transition matrix elements, $M_n/M_p$, for the $0_{gs}^{+}\to 2_1^{+}$ transitions in 48 even-even stable nuclei with $N>20$ for which electromagnetic matrix elements were compiled by Pritychenko et al. and for which high-quality inelastic proton-scattering data were available. Several deformed rare-earth nuclei have $(M_n/M_p)/(N/Z)$ values significantly below 1.0, which is not consistent with a simple liquid-drop picture. However, this phenomenon can be explained using a schematic picture in which $M_p$ reaches a maximum at proton midshell ($Z=66$) and $M_n$ reaches its maximum at neutron midshell ($N=104$). Several midmass vibrational nuclei have $M_n/M_p$ values significantly below $N/Z$, which is not consistent with the expectation that $M_n/M_p=N/Z$ in such nuclei. A shell-model investigation of these observations might yield insights about this behavior.

A microscopic statistical model based on the relativistic density functional theory (RDFT) is developed to calculate the nuclear level density (NLD). The approach employs self-consistent single-particle levels obtained from RDFT as input, incorporates pairing correlations within a finite-temperature Bardeen-Cooper-Schrieffer theory, and accounts for rotational and vibrational collective enhancement effects. The spin cut-off parameter is calculated from the single-particle levels, thereby naturally retaining the shell effects and the structural characteristics of different nuclei. Using the shape-coexisting nucleus ${}^{98}\mathrm{Sr}$ as a representative example, the microscopic origin of the deformation effect on the NLD is investigated. In addition, the calculated NLDs are systematically compared with those from various phenomenological and microscopic models, as well as with available experimental data. The results indicate that although certain discrepancies exist among different models, they exhibit consistent overall evolutionary trends. Meanwhile, the RDFT-based microscopic statistical approach is capable of providing a reasonable description of the experimental NLDs as well as the $s$- and $p$-wave neutron resonance spacings.

Background: Recent studies of the β decay of fission fragments by total absorption spectroscopy have found less decay energy attributed to leptons than previously believed, with studies of ${}^{105}\mathrm{Mo}$ and ${}^{105}\mathrm{Tc}$ being particularly impactful for reactor decay heat. These results are also crucial for interpreting measurements of reactor antineutrino energy spectra.

Purpose: To obtain complete $\beta$-decay patterns of ${}^{105}\mathrm{Mo}$, ${}^{105}\mathrm{Tc}$, ${}^{105}\mathrm{Ru}$, and ${}^{105}\mathrm{Rh}$. Determine the impact on reactor decay heat for all four isotopes and the impact on ${\overline{\nu }}_e$ emission calculation for ${}^{105}\mathrm{Mo}$ and ${}^{105}\mathrm{Tc}$.

Method: The complete $\beta$-decay intensities of ${}^{105}\mathrm{Mo}$, ${}^{105}\mathrm{Tc}$, ${}^{105}\mathrm{Ru}$, and ${}^{105}\mathrm{Rh}$ were measured with the Modular Total Absorption Spectrometer (MTAS) at Argonne National Laboratory. A beam of radioactive isobars with mass number A = 105 was produced by the CARIBU source and delivered to MTAS. Specifically, for ${}^{105}\mathrm{Mo}$, a multireflection time-of-flight device was employed to isolate a pure beam of ${}^{105}\mathrm{Mo}$ nuclides before delivery to MTAS. Highly-efficient silicon $\beta$-trigger has substantially aided the purification of the collected spectra.

Results: The mean $\beta$ and $\gamma$ energies of ${}^{105}\mathrm{Mo}$ and ${}^{105}\mathrm{Tc}$ are found to be consistent with previous TAS measurements. Differences are found in the extracted $\beta$-feeding intensities in commonly used evaluations of ${}^{105}\mathrm{Mo}$ and ${}^{105}\mathrm{Tc}$, which results in substantial differences in reactor antineutrinos detectable via inverse $\beta$ decay. Improved half-lives for ${}^{105}\mathrm{Ru}$ and ${}^{105}\mathrm{Mo}$ are also determined.

Conclusions: The number of reactor antineutrinos detectable via inverse $\beta$ decay for ${}^{105}\mathrm{Mo}$ is found to decrease by 86%, while a 37% increase is found for ${}^{105}\mathrm{Tc}$. An improved precision in the half-lives of ${}^{105}\mathrm{Ru}$ and ${}^{105}\mathrm{Mo}$ has been determined to be 4.4644(13) h, and 35.5(8) s, respectively.

The fission fragment mass and total kinetic energy (TKE) distributions of neutron deficient ${}^{193}\mathrm{Tl}$, populated in the ${}^{28}\mathrm{Si}+{}^{165}\mathrm{Ho}$ and ${}^{34}\mathrm{S}+{}^{159}\mathrm{Tb}$ reactions, have been measured at overlapping excitation energies. By employing a two-dimensional unbinned maximum likelihood fitting procedure, a substantial asymmetric fission fraction was identified across all measured energies with fragment mass centroids pointing toward the influence of deformed shell gaps near $Z\approx 36$. The extracted TKE values consistently cluster into two distinct groups, where the higher TKE associated with the asymmetric mode indicates a more compact scission configuration. While both entrance channels yield compatible asymmetric fractions, the experimental mass widths exhibit a systematic increase below the Coulomb barrier. This enhancement is more pronounced in the ${}^{28}\mathrm{Si} + {}^{165}\mathrm{Ho}$ system, potentially reflecting a “double-deformation” influence from the oblate projectile and highly prolate target. Comparisons with the general description of fission observables (GEF) model show a systematic underprediction of the asymmetric component in ${}^{193}\mathrm{Tl}$, highlighting the potential for continued development of model parameters within this transitional mass region. These results provide critical empirical constraints and demonstrate that while shell effects govern the modal structure, entrance-channel deformations significantly influence the sub-barrier fission dynamics.

Dynamical fission calculations show that the post-scission configurations resemble two collinear pear-shaped fragments whose juxtaposed surface bulges subside relatively quickly, as the fragments acquire smoother shapes. The associated rapid speed of the healing bulge surface may boost nucleons in the fragment to energies sufficient for emission. The present study explores this mechanism by following the fate of nucleons that are reflected off the inwards moving bulge surface. The simulations suggest that the mechanism may produce high-energy neutrons at the level of a few percent.

Equations of a boost-invariant and cylindrically symmetric perfect hydrodynamics are solved numerically for initial conditions inspired by the wounded nucleon model. The energy-momentum and spin tensors are used in the form that describes a relativistic massive gas governed by Boltzmann statistics. In contrast to one-dimensional boost-invariant expansion, we find a coupling between the azimuthal and longitudinal components of the electric and magnetic components of the spin polarization tensor. This feature is similar to that found earlier for the Gubser symmetry; however, our treatment allows for a more general form of initial conditions and expansion geometry. Defining the freeze-out hypersurface by the constant temperature condition, we evaluate the Pauli-Lubański four-vector and find that for the assumed geometry the only nonzero total polarization may be induced by the longitudinal component of the magnetic part of the spin polarization tensor, coupled with the azimuthal electric component. The obtained results may serve as a reference point for more realistic models of hydrodynamic expansion.

We present variable precision GP (VarP-GP), a new cost-efficient Bayesian emulator for expensive computational models with variable statistical precision. We focus on the interpretation of measurements of the quark-gluon plasma (QGP) generated in high-energy nuclear collisions, through comparison to numerical models using Bayesian Inference. Such inference calculations are computationally expensive and require surrogate model emulation, which is commonly implemented using machine learning-based Gaussian processes (GPs). Emulator training data are generated by Monte Carlo simulations whose numerical precision depends on the computational resources utilized; improved precision entails greater computational cost. This study utilizes JETSCAPE simulations of inclusive hadron and jet measurements in nuclear collisions at Relativistic Heavy Ion Collider and the Large Hadron Collider. The VarP-GP emulator combines information from multiple simulation runs with varying precision across the model parameter space, taking advantage of the smoothness in that space of quantum chromdynamics-driven processes. Comparison to a traditional emulator approach shows a marked reduction in emulator uncertainty at fixed computational cost, indicating that knowledge of the overall contours of the parameter design space is more important for precise emulation than detailed information at a more limited number of design points. As an initial application of VarP-GP, a computationally expensive model parameter sensitivity study of jet quenching data is reported. The VarP-GP emulator enables new multimodel and many-observable calibrations of QGP data and modeling, which would otherwise not be possible with achievable computing resources.