Background: Microscopic description of spontaneous fission is one of the most challenging subjects in nuclear physics. It is necessary to evaluate the collective potential and the collective inertia along a fission path for a description of quantum tunneling in spontaneous or low-energy fission. In past studies of the fission dynamics based on nuclear energy density functional (EDF) theory, the collective inertia has been evaluated with the cranking approximation, which neglects dynamical residual effects.

Purpose: The purpose is to provide a reliable and efficient method to include dynamical residual effects in the collective inertia for fission dynamics.

Methods: We use the local quasiparticle random-phase approximation (LQRPA) to evaluate the collective inertia along a fission path obtained by the constrained Hartree-Fock-Bogoliubov method with the Skyrme EDF. The finite-amplitude method (FAM) with a contour integration technique enables us to efficiently compute the collective inertia in a large model space.

Results: We evaluate the FAM-QRPA collective inertia along a symmetric fission path in ${}^{240}\mathrm{Pu}$ and ${}^{256}\mathrm{Fm}$. The FAM-QRPA inertia is significantly larger than the one of the cranking approximation and shows pronounced peaks around the ground state and the fission isomer. This is due to dynamical residual effects.

Conclusions: To describe the spontaneous or low-energy fission, we provide a reliable and efficient method to construct the collective inertia with dynamical residual effects that have been neglected in most of EDF-based works in the past. We show the importance of dynamical residual effects to the collective inertia. This work will be a starting point for a systematic study of fission dynamics in heavy and superheavy nuclei to microscopically describe the nuclear large-amplitude collective motions.

We study two different methods to prepare excited states on a quantum computer, a key initial step to study nuclear dynamics within linear-response theory. The first method uses unitary evolution for a short time $T=\mathcal{O}\left(\sqrt{1-F}\right)$ to approximate the action of an excitation operator $\widehat{O}$ with fidelity $F$ and success probability $P\approx 1-F$. The second method probabilistically applies the excitation operator using the linear combination of unitaries (LCU) algorithm. We benchmark these techniques on emulated and real quantum devices, using a toy model for thermal neutron-proton capture. Despite its larger-memory footprint, the LCU-based method is efficient even on current generation noisy devices and can be implemented at a lower gate cost than a naive analysis would suggest. These findings show that quantum techniques designed to achieve good asymptotic scaling on fault-tolerant quantum devices might also provide practical benefits on devices with limited connectivity and gate fidelity.

Background: Well-established coupled-channel (CC) and coupled reaction channel (CRC) processes make contributions to elastic scattering that are absent from local density folding models. Little is known concerning the contribution of these processes to ${}^3\mathrm{H}$ optical model potentials. For studying such processes, spin-saturated closed-shell nuclei such as ${}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}$ are particularly suitable target nuclei and the (${}^3\mathrm{H},{}^4\mathrm{He}$) reaction is easily handled within conventional reaction theory since it avoids complications such as breakup.

Purpose: To establish and characterize the contribution to the ${}^3\mathrm{H}$-nucleus interaction generated by coupling to proton pickup (outgoing ${}^4\mathrm{He}$) channels; we also study the contribution of collective states and identify effects of dynamical nonlocality due to these couplings.

Methods: CRC calculations, with CC coupling to collective states, provide the elastic channel $S$ matrix $S_{lj}$ resulting from the included processes. Inversion of $S_{lj}$ produces a local potential that yields, in a single channel calculation, the elastic-scattering observables from the CC/CRC calculation. Subtracting the bare potential yields a local and $l$-independent representation of the dynamical polarization potential (DPP). From the DPPs due to a range of channel couplings the influence of dynamically generated nonlocality can be identified.

Results: Coupling to ${}^4\mathrm{He}$ channels systematically induces repulsion and absorption in the ${}^3\mathrm{H}$ optical model potential (OMP) and generally a reduction in the rms radius of the real part. The qualitative effects, including the general undularity of the DPPs, are similar for all cases. Such coupling cannot be represented by renormalizing folding model potentials. Evidence is presented for substantial dynamical nonlocality of the induced DPPs. Local equivalent DPPs for individual couplings cannot be added to give the DPP for multiple couplings.

Conclusions: The DPPs presented here further challenge the notion that local density folding models provide a satisfactory description of elastic scattering from nuclei. Coupling to proton pickup channels induces dynamical nonlocality in the ${}^3\mathrm{H}$ OMP with implications for direct reactions involving ${}^3\mathrm{H}$. Departures from a smooth radial form for the ${}^3\mathrm{H}$ OMP should be found in good fits to suitable elastic-scattering data.

We present high-precision theoretical predictions for the electron energy spectra for the ground-state to ground-state $\beta$ decays of ${}^{214}\mathrm{Pb}$, ${}^{212}\mathrm{Pb}$, and ${}^{85}\mathrm{Kr}$ most relevant to the background of liquid xenon dark matter detectors. The effects of nuclear structure on the spectral shapes are taken into account using large-scale shell-model calculations. Final spectra also include atomic screening and exchange effects. The impact of nuclear structure effects on the ${}^{214}\mathrm{Pb}$ and ${}^{212}\mathrm{Pb}$ spectra below $\approx 100$ keV, pertinent for several searches for new physics, are found to be comparatively larger than those from the atomic effects alone. We find that the full calculation for ${}^{214}\mathrm{Pb}$ (${}^{212}\mathrm{Pb}$) predicts 15.0%–23.2% (12.1%–19.0%) less event rate in a 1–15 keV energy region of interest compared to the spectrum calculated as an allowed transition when using values of the weak axial vector coupling in the range $g_{\mathrm{A}}=0.7$–1.0. The discrepancy highlights the importance of both a proper theoretical treatment and the need for direct measurements of these spectra for a thorough understanding of $\beta$ decay backgrounds in future experiments.

Recent observations of neutron stars with gravitational waves and x-ray timing provide unprecedented access to the equation of state (EoS) of cold dense matter at densities difficult to realize in terrestrial experiments. At the same time, predictions for the EoS equipped with reliable uncertainty estimates from chiral effective field theory ($\chi \text{EFT}$) allow us to bound our theoretical ignorance. In this work, we analyze astrophysical data by using a nonparametric representation of the neutron-star EoS conditioned on $\chi \text{EFT}$ to directly constrain the underlying physical properties of the compact objects without introducing modeling systematics. We discuss how the data alone constrain the EoS at high densities when we condition on $\chi \text{EFT}$ at low densities. We also demonstrate how to exploit astrophysical data to directly test the predictions of $\chi \text{EFT}$ for the EoS up to twice nuclear saturation density, in order to estimate the density at which these predictions might break down. We find that the existence of massive pulsars, gravitational waves from $\mathrm{GW}170817$, and NICER observations of $\text{PSR}\text{J}0030+0451$ favor $\chi \text{EFT}$ predictions for the EoS up to nuclear saturation density over a more agnostic analysis by as much as a factor of seven for the quantum Monte Carlo (QMC) calculations used in this work. While $\chi \text{EFT}$ predictions using QMC are fully consistent with gravitational-wave data up to twice nuclear saturation density, NICER observations suggest that the EoS stiffens relative to these predictions at or slightly above nuclear saturation density. Additionally, for these QMC calculations, we marginalize over the uncertainty in the density at which $\chi \text{EFT}$ begins to break down, constraining the radius of a $1.4M_{\odot }$ neutron star to $R_{1.4}=11.{40}_{-1.04}^{+1.38}$ ($12.{54}_{-0.63}^{+0.71}$) km and the pressure at twice nuclear saturation density to $p\left(2n_{\mathrm{sat}}\right)=14.2_{-8.4}^{+18.1}$ ($28.7_{-15.0}^{+15.3}$) $\mathrm{MeV}/{\mathrm{fm}}^3$ with massive pulsar and gravitational-wave (and NICER) data.

The energy density is calculated in coordinate space for ${}^{12}\mathrm{C}$, ${}^{40}\mathrm{Ca}$, ${}^{48}\mathrm{Ca}$, and ${}^{208}\mathrm{Pb}$ using a dispersive optical model constrained by all relevant data including the corresponding energy of the ground state. The energy density of ${}^8\mathrm{Be}$ is also calculated using the Green's-function Monte Carlo method employing the Argonne-Urbana two- and three-body interactions. The nuclear interior minimally contributes to the total binding energy due to the $4\pi r^2$ phase-space factor. Thus, the volume contribution to the energy in the interior is not well constrained. The dispersive-optical-model energy densities are in good agreement with ab initio self-consistent Green's-function calculations of infinite nuclear matter restricted to treat only short-range and tensor correlations. These results call into question the degree to which the equation of state for nuclear matter is constrained by the empirical mass formula. In particular, the results in this paper indicate that saturated nuclear matter does not require the canonical value of 16-MeV binding per particle but only about 13–14 MeV when the interior of ${}^{208}\mathrm{Pb}$ is considered.

We develop an effective field theory (EFT) for deformed odd-mass nuclei. These are described as an axially symmetric core to which a nucleon is coupled. In the coordinate system fixed to the core the nucleon is subject to an axially symmetric potential. Power counting is based on the separation of scales between low-lying rotations and higher-lying states of the core. In leading order, core and nucleon are coupled by universal derivative terms. These comprise a covariant derivative and gauge potentials which account for Coriolis forces and relate to Berry-phase phenomena. At leading order, the EFT combines the particle-rotor and Nilsson models. We work out the EFT up to next-to-leading order and illustrate the results in ${}^{239}\mathrm{Pu}$ and ${}^{187}\mathrm{Os}$. At leading order, odd-mass nuclei with rotational bandheads that are close in energy and differ by one unit of angular momentum are triaxially deformed. For bandheads that are well separated in energy, triaxiality becomes a subleading effect. The EFT developed in this paper presents a model-independent approach to the particle-rotor system that is capable of systematic improvement.

The direct Urca process of rapid neutrino emission can occur in nonuniform nuclear pasta phases that are expected in the inner crusts of neutron stars. Here, the periodic potential for a nucleon in nuclear pasta allows momentum conservation to be satisfied for direct Urca reactions. We improve on earlier work by modeling a rich variety of pasta phases (gnocchi, waffle, lasagna, and anti-spaghetti) with large-scale molecular dynamics simulations. We find that the neutrino luminosity due to direct Urca reactions in nuclear pasta can be 3 to 4 orders of magnitude larger than that from the modified Urca process in the NS core. Thus neutrino radiation from pasta could dominate radiation from the core and this could significantly impact the cooling of neutron stars.

A new critical survey of all half-life, decay-energy, and branching-ratio measurements related to 23 superallowed $0^{+}\to 0^{+}\beta$ decays is presented. Included are 222 individual measurements of comparable precision obtained from 174 published references. Compared with our last survey in 2015, we have added results from 28 new publications and eliminated an approximately equal number whose results have been superseded by much more precise modern data. We obtain world-average $ft$ values for each of the 21 transitions that have a complete set of data and then apply radiative and isospin-symmetry-breaking corrections to extract “corrected” $\mathcal{F}t$ values. Fifteen of these $\mathcal{F}t$ values now have a precision of $0.3\%$ or better and all take the same value within statistics, as expected from conservation of the vector current. Their average, $\overline{\mathcal{F}t}$, when combined with the muon lifetime, yields the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa matrix, $V_{\mathit{ud}}=0.97373\pm 0.00031$. This is lower than our 2015 result by one standard deviation and its uncertainty is increased by $50\%$. This is a consequence not of any shifts in the experimental data but of new calculations for the radiative corrections. The lower $V_{\mathit{ud}}$ value now leads to greater tension in the top-row test of unitarity in the CKM matrix. Updates in experimental data have independently led to a factor-of-two tighter limit being set on the possible existence of a scalar interaction. The new limit on Fierz interference is $b_F\le$ 0.0033 at the $90\%$ confidence level.

Background: Spectroscopic factors, overlaps, and isospin symmetry are often used in conjunction with single-particle wave functions for the phenomenological analysis of nuclear structure and reactions. Many differing prescriptions for connecting these quantities to physically relevant asymptotic normalization constants or widths are available in the literature, but their relationship and degree of validity are not always clear.

Purpose: This paper derives relationships among the above quantities of interest using well-defined methodology and starting assumptions.

Method: $R$-matrix theory is used as the primary tool to interoperate among the quantities of interest to this work. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated.

Results: Relationships between the quantities of interest are derived. Example applications of these methods to mirror levels in nucleon $+ {}^{12}\mathrm{C}$, nucleon $+ {}^{16}\mathrm{O}$, and nucleon $+ {}^{26}\mathrm{Al}$ are presented. A new approach to multilevel mirror symmetry is derived and applied to the first three $2^{+}$ states of ${}^{18}\mathrm{O}$ and ${}^{18}\mathrm{Ne}$.

Conclusions: The relationship between the quantities of interest is clarified and certain procedures are recommended. It is found that the asymptotic normalization constant of the second $2^{+}$ state in ${}^{18}\mathrm{Ne}$ deduced from the mirror state in ${}^{18}\mathrm{O}$ is significantly larger than found in previous work. This finding has the effect of increasing the ${}^{17}\mathrm{F}(p,\gamma ){}^{18}\mathrm{Ne}$ reaction rate in novae.

We present STAR measurements of strange hadron (${\mathrm{K}}_S^0, \mathrm{\Lambda }, \overline{\mathrm{\Lambda }}, {\mathrm{\Xi }}^{-}, {\overline{\mathrm{\Xi }}}^{+}, {\mathrm{\Omega }}^{-}, {\overline{\mathrm{\Omega }}}^{+}$, and $\varphi$) production at midrapidity ($\left|y\right|<0.5$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{NN}}}$ = 7.7–39 GeV from the Beam Energy Scan Program at the Relativistic Heavy Ion Collider (RHIC). Transverse-momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios ($\overline{\mathrm{\Lambda }}/\mathrm{\Lambda }, {\overline{\mathrm{\Xi }}}^{+}/{\mathrm{\Xi }}^{-}, {\overline{\mathrm{\Omega }}}^{+}/{\mathrm{\Omega }}^{-}$) are presented as well and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out (${\mu }_B/T_{\mathrm{ch}}$ and ${\mu }_S/T_{\mathrm{ch}}$) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors ($R_{\text{CP}}$) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The ${\mathrm{K}}_S^0 R_{\text{CP}}$ shows no suppression for $p_T$ up to 3.5 $\mathrm{GeV}/c$ at energies of 7.7 and 11.5 GeV. The $\overline{\mathrm{\Lambda }}/{\mathrm{K}}_S^0$ ratio also shows baryon-to-meson enhancement at intermediate $p_T$ ($\approx 2.5 \mathrm{GeV}/c$) in central collisions at energies above 19.6 GeV. Both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.

We use the finite-amplitude method (FAM), an efficient implementation of the quasiparticle random phase approximation, to compute $\beta$-decay rates with Skyrme energy-density functionals for 3983 nuclei, essentially all the medium-mass and heavy isotopes on the neutron-rich side of stability. We employ an extension of the FAM that treats odd-mass and odd-odd nuclear ground states in the equal filling approximation. Our rates are in reasonable agreement both with experimental data where available and with rates from other global calculations.

In the shell-model framework, valence-space Hamiltonians connecting multiple major-oscillator shells are of key interest for investigating the physics of neutron-rich nuclei, which have been the subject of intense experimental activity for decades. Here we present an extension of the ab initio valence-space in-medium similarity renormalization group, which allows the derivation of such Hamiltonians nonperturbatively. Starting from initial two- and three-nucleon forces from chiral effective field theory, we then calculate properties of nuclei in the important island-of-inversion region above oxygen, so far unexplored with ab initio methods. Our results in the neon and magnesium isotopes indicate the importance of neutron excitation from the $sd$ to $pf$ shells and ground states dominated by intruder configurations around $N=20$, consistent with the conclusions from phenomenological studies. We also benchmark the excitation spectrum of ${}^{16}\mathrm{O}$ with coupled-cluster theory, finding generally good agreement, and discuss implications for ground-state energies and charge radii in oxygen and calcium isotopes. Finally we outline the proper procedure for treating the longstanding issue of center-of-mass contamination, and show that with a particular choice of valence space, these spurious states can be removed successfully.

We propose observables $v_0$ and $v_0\left(p_T\right)$ which quantify the relative fluctuations in the total transverse momentum at fixed multiplicity. We first study the factorization of the fixed multiplicity momentum-dependent two-particle correlation function into a product of $v_0\left(p_T^a\right)$ and $v_0\left(p_T^b\right)$ within realistic hydrodynamic simulations. Then we present computations of $v_0\left(p_T\right)$ for different particle types. We determine the relation between the integrated $v_0$ and previously measured observables and compare results from a hybrid hydrodynamics-based model to experimental data. The effects of bulk viscosity and an initial pre-equilibrium stage on the results are quantified. We find that $v_0$ is strongly correlated with the initial state entropy per elliptic area, $S/A$. Using this result, we explain how the observed correlations between the elliptic flow and the transverse momentum (both in simulations and experiment) reflect the initial state correlations between $1/A$ and ellipticity ${\varepsilon }_2$ at fixed multiplicity. We argue that the systematic experimental study of $v_0$, with the same sophistication as used for the other $v_n$, can contribute significantly to our understanding of quark gluon plasma properties.

We present an analysis of proton-number fluctuations in $\sqrt{s_{NN}}=2.4 \mathrm{GeV}$ ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. With the help of extensive detector simulations done with Isospin Quantum Molecular Dynamics (IQMD) transport model events including nuclear clusters, various nuisance effects influencing the observed proton cumulants have been investigated. Acceptance and efficiency corrections have been applied as a function of fine-grained rapidity and transverse momentum bins, as well as considering local track density dependencies. Next, the effects of volume changes within particular centrality selections have been considered and beyond-leading-order corrections have been applied to the data. The efficiency and volume-corrected proton number moments and cumulants $K_n$ of orders $n=1, 2, 3, \mathrm{and} 4$ have been obtained as a function of centrality and phase-space bin, as well as the corresponding correlators $C_n$. We find that the observed correlators show a power-law scaling with the mean number of protons, i.e., $C_n\propto {\langle N\rangle }^n$, indicative of mostly long-range multiparticle correlations in momentum space. We also present a comparison of our results with Au $+$ Au collision data obtained at the Relativistic Heavy Ion Collider (RHIC) at similar centralities but higher $\sqrt{s_{NN}}$.

We report quantum Monte Carlo calculations of weak transitions in $A\le 10$ nuclei, based on the Norfolk two- and three-nucleon chiral interactions, and associated one- and two-body axial currents. We find that the contribution from two-body currents is at the 2–3% level, with the exception of matrix elements entering the rates of ${}^8\mathrm{Li}$, ${}^8\mathrm{B}$, and ${}^8\mathrm{He}$ $\beta$ decay. These matrix elements are suppressed in impulse approximation based on the (leading order) Gamow Teller transition operator alone; two-body currents provide a $20–30\%$ correction, which is, however, insufficient to bring theory in agreement with experimental data. For the other transitions, the agreement with the data is satisfactory, and the results exhibit a negligible to mild model dependence when different combinations of Norfolk interactions are utilized to construct the nuclear wave functions. We report a complete study of two-body weak transition densities which reveals the expected universal behavior of two-body currents at short distances throughout the range of $A=3$ to $A=10$ systems considered here.

Relativistic quantum molecular dynamics based on the relativistic mean field theory (RQMD.RMF) is extended by including momentum-dependent potential. The equation of state (EoS) dependence of the directed and the elliptic flow of protons in the beam energy range of $2.3<\sqrt{s_{NN}}<20$ GeV is examined. It is found that the directed flow depends strongly on the optical potential at high energies, $\sqrt{s_{NN}}>3$ GeV, where no information is available experimentally. The correlation between effective mass at saturation density and the optical potential is found: smaller values of effective mass require smaller strengths of the optical potential to describe the directed flow data. This correlation can also be seen in the beam energy dependence of the elliptic flow at $\sqrt{s_{NN}}>3$ GeV, although its effect is rather weak. On the other hand, stiff EoS is required to describe the elliptic flow at lower energies. Experimental constraints on the optical potential from $pA$ collisions will provide important information on the EoS at high energies. The proton directed and the elliptic flow are well described in the RQMD.RMF model from $\sqrt{s_{NN}}=2.3$ to 8.8 GeV. In contrast, to reproduce the collapse of the directed flow above 10 GeV, pressure has to be reduced, which indicates a softening of the EoS around $\sqrt{s_{NN}}=10$ GeV.

The nonrelativistic reduction of the self-consistent covariant density functional theory is realized for the first time with the similarity renormalization group method. The reduced nonrelativistic Hamiltonian and densities are calculated by solving the corresponding flow equations with a novel expansion in terms of the inverse of the Dirac effective mass. The efficiency and accuracy of this newly proposed framework have been demonstrated for several typical spherical nuclei. It is found that the exact solutions of the total energies, traces of vector and scalar densities, and the root-mean-square radii are reproduced quite well for all nuclei. This allows one to directly compare and bridge the relativistic and nonrelativistic nuclear energy density functional theories in the future.

Transfer reactions provide information about the single-particle nature of nuclear levels. In particular, the differential cross sections from these measurements are sensitive to the angular momentum of the transferred particle and the spectroscopic factor of the populated level. However, the process of extracting these properties is subject to uncertainties, both from experimental and theoretical sources. By integrating the distorted wave Born approximation into a Bayesian model, we propagate these uncertainties through to the spectroscopic factors and orbital angular momentum values. We use previously reported data of the proton pickup reaction ${}^{70}\mathrm{Zn}(d,{}^{3}He){}^{69}\mathrm{Cu}$ as an example. By accounting for uncertainties in the experimental data, optical model parameters, and reaction mechanism, we find that the extracted spectroscopic factors for low-lying states of ${}^{69}\mathrm{Cu}$ are subject to large, asymmetric uncertainties ranging from 35 to $108\%$. Additionally, Bayesian model comparison is employed to assign probabilities to each of the allowed angular momentum transfers. This method confirms the assignments for many states, but suggests that the data for a state lying at 3.70 MeV are better characterized by an $\ell =3$ transfer, rather than the previously reported $\ell =2$.

The overlap in the mass symmetric region of the reaction products from fusion-fission and quasifission complicates the assignment of symmetric events to complete fusion on the basis of the mass distribution alone. Additional observables, besides mass distribution, should be used. The approach proposed here relies on the fact that fusion-fission and quasifission are characterized by different timescales. Within this framework, we performed a detailed study to find out how timescales can be probed via angular momentum transfer as measured via $\gamma$-ray multiplicities. The proof of principle was carried out by measuring the $\gamma$ rays in coincidence with fusion-fission and quasielastic binary fragments in the reaction ${}^{32}\mathrm{S}$ $+$ ${}^{197}\mathrm{Au}$ at beam energy near the Coulomb barrier. The experiment was performed at the Accélérateur Linéaire Tandem à Orsay (ALTO) facility at the Institut De Physique Nucléaire (IPN) in Orsay (France) using a detection setup consisting of ORGAM (ORsay GAMma) and PARIS (Photon Array Radioactive Ion Stable beams) $\gamma$-detectors arrays coupled with the CORSET (CORrelation SETup) time-of-flight spectrometer. Results of the sensitivity of this method to distinguish reaction channels with different dynamics are discussed.