The renormalization of iterated one-pion exchange (OPE) is studied in chiral effective field theory $\left(\chi \mathrm{EFT}\right)$ for the antinucleon-nucleon $\left(\overline{N}N\right)$ system. The OPE potential is cut off at a certain distance and contact interactions are represented by a complex spherical well with the same radius. We investigate the dependence on the cutoff radius of the phase shifts, inelasticities, and mixing angles for the low partial waves in $\overline{N}N$ scattering. We show that renormalization requires additional contact interactions compared to the expectation based on naive dimensional analysis. Results after renormalization are compared with the state-of-the-art energy-dependent partial-wave analysis of $\overline{N}N$ data. We compare our conclusions with applications of $\chi \mathrm{EFT}$ to the nucleon-nucleon system.

The exotic $\beta$-delayed proton emission is calculated in ${}^{11}\mathrm{Be}$ from first principles using chiral two- and three-nucleon forces. To investigate the unexpectedly large branching ratio measured in Ayyad et al. [Phys. Rev. Lett. 123, 082501 (2019)], we calculate the proposed $(1/2^{+},1/2)$ proton resonance in ${}^{11}\mathrm{B}$ using the no-core shell model with continuum. This calculation helps to address whether this enhancement is caused by unknown dark decay modes or an unobserved proton resonance. We report a branching ratio of $b_p=(1.3\pm 0.5)\times {10}^{-6}$, suggesting that its unexpectedly large value is caused by an unobserved proton resonance in ${}^{11}\mathrm{B}$.

The nonlocalized cluster model provides a new perspective for describing nuclear cluster effects and has been successfully applied in the study of cluster structures in bound states, scattering states, and also resonant states. However, there is still some room for development when dealing with resonance problems with this new model. The complex scaling method (CSM) is an important method in research of the resonant states. We combine CSM with the nonlocalized cluster model [B. Zhou et al., Phys. Rev. Lett. 110, 262501 (2013)] for the first time, and such combination provides a new way to study the resonance in the nonlocalized cluster model. Here, we apply the CSM to ${}^8\mathrm{Be}$ as a simple example to illustrate its usages and advantages, while pointing out that the generalization to more complicated cluster systems is also natural.

We present the equation of state of infinite neutron matter as obtained from highly realistic Hamiltonians that include nucleon-nucleon and three-nucleon coordinate-space potentials. We benchmark three independent many-body methods: Brueckner-Bethe-Goldstone (BBG), Fermi hypernetted chain/single-operator chain (FHNC/SOC), and auxiliary-field diffusion Monte Carlo (AFDMC). We find them to provide similar equations of state when the Argonne $v_{18}$ and the Argonne $v_6^{\prime }$ nucleon-nucleon potentials are used in combination with the Urbana IX three-body force. Only at densities larger than about 1.5 the nuclear saturation density (${\rho }_0=0.16{\mathrm{fm}}^{-3}$) the FHNC/SOC energies are appreciably lower than the other two approaches. The AFDMC calculations carried out with all of the Norfolk potentials fitted to reproduce the experimental trinucleon ground-state energies and $nd$ doublet scattering length yield unphysically bound neutron matter, associated with the formation of neutron droplets. Including tritium $\beta$ decay in the fitting procedure, as in the second family of Norfolk potentials, mitigates but does not completely resolve this problem. An excellent agreement between the BBG and AFDMC results is found for the subset of Norfolk interactions that do not make neutron-matter collapse, while the FHNC/SOC equations of state are moderately softer.

Background: Heavy-ion fusion reactions play a crucial role in various aspects of nuclear physics and astrophysics. The nuclear interaction potential and hence the fusion barrier formed between the interacting nuclei are the keys to understanding the complex fusion process dynamics. Thus, a theoretical investigation of fusion barrier characteristics which includes the relativistic effects is of paramount significance.

Purpose: This work intends to explore the fusion barrier characteristics of different target-projectile combinations within the relativistic mean-field (RMF) formalism. The M3Y nucleon-nucleon (NN) potential is compared with the relativistic R3Y and density-dependent R3Y (DDR3Y) NN potentials within the double folding approach. A systematic study is carried out to study the effect of different RMF density distributions and effective NN interactions on the fusion and/or capture cross section of 24 target-projectile combinations leading to heavy and superheavy nuclei (SHN).

Methods: The density distributions of interacting nuclei and the microscopic R3Y NN interaction are obtained from the RMF formalism for nonlinear NL1, NL3, and TM1 parameter sets and the relativistic Hartree-Bogoliubov (RHB) approach for the DDME2 parameter set. The medium-independent relativistic R3Y, the density-dependent DDR3Y, and widely adopted M3Y NN potentials are used to obtain the nuclear interaction potential within the double folding approach. The densities for the projectiles and targets are obtained from the relativistic mean-field approaches. The fusion and/or capture cross section for the different reaction systems is calculated using the well-known $\ell$-summed Wong model.

Results: The barrier height and position of 24 heavy-ion reaction systems are obtained for different nuclear density distributions and effective NN interaction potentials. We have considered the lighter mass projectile and heavier mass target combinations for synthesizing exotic drip-line nuclei, including the superheavy nuclei (SHN). These reactions include the even-even ${}^{48}\mathrm{Ca}+{}^{154}\mathrm{Sm}$, ${}^{48}\mathrm{Ca}+{}^{238}\mathrm{U}$, ${}^{48}\mathrm{Ca}+{}^{248}\mathrm{Cm}$, and ${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$; even-odd ${}^{46}\mathrm{K}+{}^{181}\mathrm{Ta}$; odd-odd ${}^{31}\mathrm{Al}+{}^{197}\mathrm{Au}$ and ${}^{39}\mathrm{K}+{}^{181}\mathrm{Ta}$; and also 17 other systems for the synthesis of SHN $Z=120$. The comparison of fusion and/or capture cross section obtained from the $\ell$-summed Wong model is made with the available experimental data.

Conclusions: The phenomenological M3Y NN potential is observed to give higher barrier heights than the relativistic R3Y NN potential for all the reaction systems. The comparison of results obtained from different relativistic parameter sets shows that the densities from NL1 and TM1 parameter sets give the lowest and highest barrier heights for all the systems under study. The density dependent DDR3Y NN potential is obtained within the relativistic Hartree-Bogoliubov approach for the DDME2 parameter set. We observed higher barrier heights and lower cross sections for the DDR3Y NN potential as compared to density-independent R3Y NN potentials obtained for considered nonlinear NL1, NL3, and TM1 parameter sets. According to the present analysis, it is concluded that the NL1 and NL3 parameter sets provide comparatively better overlap with the experimental fusion and/or capture cross section than the TM1 and DDME2 parameter sets.

Background: The relevance of including channel coupling effects in the form of target deformation and vibration in fusion reactions has been well established. Many reactions with positive $Q$ values for neutron transfer show enhancement in sub-barrier fusion cross sections. However, there are exceptions to these cases.

Purpose: We aim to make a comprehensive list of factors influencing the sub-barrier fusion enhancement in systems with neutron transfer channels having positive $Q$ values.

Method: Evaporation residue cross sections were measured for ${}^{18}\mathrm{O}+{}^{182,184,186}\mathrm{W}$ reactions in the energy range $68–104$ MeV in the laboratory frame, using a recoil mass spectrometer.

Results: Inclusion of deformation of target and projectile low-level excitations in the coupled channels calculations explains the measured fusion excitation functions of ${}^{18}\mathrm{O}+{}^{182,184,186}\mathrm{W}$ reactions.

Conclusions: Considering that all the targets have similar deformation, and comparing with ${}^{16}\mathrm{O}+{}^{182,184,186}\mathrm{W}$ reactions having negative $2n$ transfer $Q$ values, we can conclude that the positive $Q$ values of neutron transfer channels have no effect on the observed fusion cross sections of ${}^{18}\mathrm{O}+{}^{182,184,186}\mathrm{W}$ reactions.

High accuracy measurements in Mössbauer transitions open up the possibility to use them in the search for temporal and spatial variations of the fine structure constant $\alpha$, quark mass $m_q$, and dark matter field which may lead to the variations of $\alpha$ and $m_q$. We calculate the sensitivity of nuclear transitions to variations of $\alpha$ and $m_q$. Mössbauer transitions have high sensitivity to variation of quark mass $m_q$ and the strong interaction scale ${\mathrm{\Lambda }}_{\mathrm{QCD}}$ to which atomic optical clocks are not sensitive. The enhancement factors $K$, defined by $\frac{\delta f}{f}=K_{\alpha }\frac{\delta \alpha }{\alpha }$ and $\frac{\delta f}{f}=K_q\frac{\delta m_q}{m_q}$ where $f$ is the transition energy, may be large in some transitions. The 8-eV nuclear clock transition in ${}^{229}\mathrm{Th}$ $(K_q\approx {10}^4)$ and 76-eV transition in ${}^{235}\mathrm{U}$ $(K_{\alpha }\approx K_q\approx {10}^3)$ may be investigated using laser spectroscopy methods.

The ${}^{10}\mathrm{B}+n$ system has been studied by measuring charged particles from neutron-induced reactions in the 1 to 20 MeV energy range. Protons, deuterons, tritons, and $\alpha$ particles were measured at four angles using the pulsed white neutron spectrum at the Los Alamos Neutron Science Center Weapons Neutron Research facility. Differential cross sections for each species are reported. These new data are combined with literature data in an $R$-matrix analysis of the ${}^{11}\mathrm{B}$ compound system. A comparison is made to the molecular and cluster states candidates observed in these reactions.

We present developments and applications for the diagonalization of shell-model Hamiltonians in a discrete nonorthogonal basis. The method, and its actual numerical implementation carina, based on mean-field and beyond-mean-field techniques, has already been applied in previous studies and is focused on basis states selection optimization. The method is benchmarked against a full set of $sd$ shell exact diagonalizations, and is applied for the first time to the heavy deformed ${}^{254}\mathrm{No}$ nucleus.

Single-particle and collective excitations in ${}^{66}\mathrm{Zn}$ have been investigated via the multinucleon transfer reaction, ${}^{26}\mathrm{Mg}({}^{48}\mathrm{Ca}$, $\alpha 4n\gamma$) using the Gammasphere multidetector array and the Fragment Mass Analyzer. In addition to confirming and complementing the previously known low-spin structure, a new quasirotational band comprising several stretched $E2$ transitions has been established to high spins. However, due to fragmentary nature of its decay, it was not possible to link this sequence to the low-lying states and, thus, determine the absolute excitation energies, spins, and parities unambiguously. Large-scale shell-model calculations employing the JUN45 and jj44b effective interactions are able to successfully describe the low-spin structure and herewith confirm that it is dominated by single-particle excitations. The newly established rotational cascade is compared with known superdeformed bands in the $A\approx 60\text{–}70$ mass region, and with results of calculations performed within the frameworks of the cranked shell model and the adiabatic and configuration-fixed constrained covariant density functional theory and the quantum particle-rotor model.

The understanding of fusion probability is of particular importance to reveal the mechanism of producing superheavy elements. We present a microscopic study of compound-nucleus formation by combining time-dependent density-functional theory, the coupled-channels approach, and dynamical diffusion models. The fusion probability and compound-nucleus formation cross sections for cold-fusion reactions ${}^{48}\mathrm{Ca}+{}^{208}\mathrm{Pb}, {}^{50}\mathrm{Ti}+{}^{208}\mathrm{Pb}$, and ${}^{54}\mathrm{Cr}+{}^{208}\mathrm{Pb}$ are investigated and it is found that the deduced capture barriers and capture cross sections for these reactions are consistent with experimental data. Above the capture barrier, our calculations reproduce the measured fusion probability reasonably well. Our studies demonstrate that the restrictions from the microscopic dynamics theory improve the predictive power of the coupled-channels and diffusion calculations.

Background: Charge-exchange reactions are a powerful tool for exploring nuclear structure and nuclear astrophysics; however, a robust charge-exchange reaction theory with quantified uncertainties is essential for extracting reliable physics.

Purpose: The goal of this work is to determine the uncertainties due to optical potentials used in the theory for charge-exchange reactions to isobaric analog states.

Method: We implement a two-body reaction model to study $(p,n)$ charge-exchange transitions and perform a Bayesian analysis. The $(p,n)$ reaction to the isobaric analog states of ${}^{14}\mathrm{C}$, ${}^{48}\mathrm{Ca}$, and ${}^{90}\mathrm{Zr}$ targets are studied over a range of beam energies. We compare predictions using standard phenomenological optical potentials with those obtained microscopically.

Results: Charge-exchange cross sections are reasonably reproduced by modern optical potentials. However, when uncertainties in the optical potentials are accounted for, the resulting predictions of charge-exchange cross sections have very large uncertainties.

Conclusions: The charge-exchange reaction cross section is strongly sensitive to the input interactions, making it a good candidate to further constrain nuclear forces and aspects of bulk nuclear matter. However, further constraints on the optical potentials are necessary for a robust connection between this tool and the underlying isovector properties of nuclei.

Within a class of models in which lepton flavor violation is induced dominantly by scalar particle exchanges, we estimate the $\mu \to e$ conversion rate in several nuclei. We include next-to-leading order (NLO) terms in the one- and two-nucleon interactions in chiral effective theory, rectifying some incorrect results in the previous literature. We provide an uncertainty budget for the conversion rates and we find that NLO contributions affect the amplitudes at the level of $10\%$, which could be larger than the uncertainty on the leading order couplings, dominated by the strange and nonstrange nucleon sigma terms. We study the implications of our results for testing Higgs-mediated charged lepton flavor violation (CLFV) in the future by combining results from various experimental searches, such as $\mu \to e$ conversion in multiple target nuclei and $\mu \to e\gamma$.

In the inner crust of neutron stars one expects phases in which nuclei adopt rodlike and platelike forms, so-called pasta phases. For ordered phases, the superfluid density of nucleons is anisotropic and in this paper we calculate the effective superfluid density of disordered pasta phases. We use an effective medium approach which parallels that previously used for calculating the electrical conductivity of terrestrial matter. We allow for the effect of entrainment, the fact that the current density of one species of nucleon depends on the gradient of the phase of the condensate pair wave function not only of the same species but also of the other species. We find that for protons, the results of the effective medium formalism can be quite different from those of simple approximations.

The nucleon-nucleon short-range correlation (NN-SRC) is one of the key issues of nuclear physics, which typically manifest themselves in high-momentum components of the nuclear momentum distributions. In this paper, the nuclear spectral functions based on the axially deformed relativistic mean-field model are developed to involve the NN-SRC. With the spectral functions, the inclusive electron scattering $(e,e^{\prime })$ cross sections are calculated within the plane-wave impulse approximation (PWIA) framework, including the quasielastic (QE) part and $\mathrm{\Delta }$ production part. Especially in the $\mathrm{\Delta }$ production region, we reconsider the electromagnetic structures of the nucleon resonance $\mathrm{\Delta }$(1232) and the scattering mechanisms, and thereby the theoretical calculations are improved effectively and the cross sections are well consistent with the experimental data. The theoretical $(e,e^{\prime })$ cross sections are further divided into NN-SRC and mean-field contributions. It is found that, at the kinematics $0.5{\mathrm{GeV}}^2<Q^2<1{\mathrm{GeV}}^2$, the QE peak and $\mathrm{\Delta }$ production peak not only reflect the mean-field structure but also are sensitive to the NN-SRC information. Finally, we provide another method to extract the strengths of NN-SRC from experimental cross sections for selected nuclei at the suitable kinematics.

We differentiate the event-by-event $n\text{−}\gamma$ multiplicity data from ${}^{252}\mathrm{Cf}\left(\mathrm{sf}\right)$ with respect to the energies of the emitted particles as well as their relative angles of emission. We determine that neutron emission enhances $\gamma$-ray emission around 0.7 and 1.2 MeV, but the only directional alignment was observed for $E_{\gamma }\le 0.7$ MeV and tended to be parallel and antiparallel to neutrons emitted in the same event. The emission of $\gamma$ rays at other energies was determined to be nearly isotropic. The presence of the emission and alignment enhancements is explained by positive correlations between neutron emission and quadrupole $\gamma$-ray emission along rotational bands in the de-exciting fragments. This observation corroborates the hypothesis of positive correlations between the angular momentum of a fragment and its intrinsic excitation energy. The results of this work are especially relevant in view of the recent theoretical and experimental interest in the generation of angular momentum in fission. Specifically, we have determined an alignment of the fragment's angular momenta in a direction perpendicular to the direction of motion. We interpret the lack of $n\text{−}\gamma$ angular correlations for fission fragments near closed shells as a weakening of the alignment process for spherical nuclei. Lastly, we have observed that statistical $\gamma$ rays are emitted isotropically, indicating that the average angular momentum removed by this radiation is small. These results, and the analysis tools presented in this work, represent a stepping stone for future analysis of $n\text{−}\gamma$ emission correlations and their connection to angular momentum properties.

A mass spectroscopy experiment with a pair of nearly identical high-resolution spectrometers and a tritium target was performed in Hall A at Jefferson Lab. Utilizing the $(e,e^{\prime }{K}^{+})$ reaction, enhancements, which may correspond to a possible $\mathrm{\Lambda }nn$ resonance and a pair of $\mathrm{\Sigma }NN$ states, were observed with an energy resolution of about 1.21 MeV ($\sigma$), although greater statistics are needed to make definitive identifications. An experimentally measured $\mathrm{\Lambda }nn$ state may provide a unique constraint in determining the $\mathrm{\Lambda }n$ interaction, for which no scattering data exist. In addition, although bound $A=3$ and 4 $\mathrm{\Sigma }$ hypernuclei have been predicted, only an $A=4 \mathrm{\Sigma }$ hypernucleus (${}_{\mathrm{\Sigma }}{}^4\mathrm{He}$) was found, utilizing the $(K^{-},{\pi }^{-})$ reaction on a ${}^4\mathrm{He}$ target. The possible bound $\mathrm{\Sigma }NN$ state is likely a ${\mathrm{\Sigma }}^{0}nn$ state, although this has to be confirmed by future experiments.

Similarity renormalization group (SRG) is combined with the relativistic mean-field (RMF) theory, the Schrödinger-like Hamiltonian describing the motion of nucleon is obtained. The Hamiltonian with the scalar and vector potential from the self-consistent RMF calculations is used to explore the pseudospin and spin symmetries and their evolution with mass number for Sn isotopes. The contribution of every term to the pseudospin (spin) energy splitting is extracted. The spin energy splitting comes almost entirely from spin-orbit coupling, whereas the pseudospin energy splitting is also dominated by nonrelativistic and dynamical terms. The magnitude of the splitting is related to the radial, angular, and isospin quantum numbers of the doublet. The isospin dependence of pseudospin (spin) symmetry comes from the nonrelativistic term (the spin-orbit coupling). The pseudospin symmetry of neutron is superior to that of proton from the weakening of nonrelativistic and dynamical breaking. These results are helpful to understand the origin and breaking mechanism of pseudospin and spin symmetries.

Fusion excitation functions have been measured for ${}^{16}\mathrm{O}+{}^{61}\mathrm{Ni}$ and ${}^{18}\mathrm{O}+{}^{61,62}\mathrm{Ni}$ systems around the Coulomb barrier ($\approx 0.7V_B$–$1.3V_B$) using the recoil mass spectrometer, heavy ion reaction analyzer. The ground state $Q$ value for two neutron stripping is positive for both systems with ${}^{18}\mathrm{O}$ as the projectile. Strong enhancement of the experimental fusion cross sections were observed below the barrier for all the systems compared to that of the predictions of the one-dimensional barrier penetration model. To understand such enhancement, a coupled-channels formalism has been used. A comparative study of these systems indicated that the coupling of two neutron transfer channels with the collective excitations could play the role behind the sub-barrier fusion enhancement for ${}^{18}\mathrm{O}$ induced reactions. However, the sub-barrier enhancement for ${}^{16}\mathrm{O} + {}^{61}\mathrm{Ni}$ is found to be due to the coupling of quadrupole vibrations of both the interacting nuclei. Also after comparing these systems with other systems of different Ni isotopes, we have found that the signature of the role of coupling to neutron transfer channels due to ground state positive $Q$ value for neutron transfer is ambiguous.

We study the space-time evolution of electric E and magnetic B fields along with the electromagnetic anomaly $(\mathbf{E}·\mathbf{B})$ in the presence of electric ($\sigma$) and chiral magnetic (${\sigma }_{\chi }$) conductivities in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. By comparing with the Lienard-Wiechert solutions with zero conductivities, we observe a symmetry breaking of the electromagnetic field in a conducting medium with respect to the reaction plane. The decay of the field is also significantly decelerated after the conductivities are introduced. Similar effects are also found for the dipole structure of $\mathbf{E}·\mathbf{B}$ as well as the quadrupole structure of $(\mathbf{E}·\mathbf{B})\mathbf{B}$, which may finally affect the charge separation of the elliptic flow coefficient of hadrons observed in high-energy nuclear collisions.