Nuclear Theory·nucl-th

Friday·February 5, 2021

10 papers—6 primary·4 cross-listed

01
$^{229 m}$ Th isomer from a nuclear model perspective
Nikolay Minkov🇧🇬 · Adriana Pálffy🇩🇪
The physical conditions for the emergence of the extremely low-lying nuclear isomer $^{229 m}$ Th at approximately 8 eV are investigated in the framework of our recently proposed nuclear structure model. Our theoretical approach explains the $^{229 m}$ Th-isomer phenomenon as the result of a very fine interplay between collective quadrupole-octupole and single-particle dynamics in the nucleus. We find that the isomeric state can only appear in a rather limited model space of quadrupole-octupole deformations in the single-particle potential, with the octupole deformation being of a crucial importance for its formation. Within this deformation space the model-described quantities exhibit a rather smooth behaviour close to the line of isomer-ground state quasi-degeneracy determined by the crossing of the corresponding single-particle orbitals. Our comprehensive analysis confirms the previous model predictions for reduced transition probabilities and the isomer magnetic moment, while showing a possibility for limited variation in the ground-state magnetic moment theoretical value. These findings prove the reliability of the model and suggest that the same dynamical mechanism could manifest in other actinide nuclei giving a general prescription for the search and exploration of similar isomer phenomena.
nucl-thnucl-exPRC(2021)·30 citations
02
Two- and three-nucleon contact interactions and ground-state energies of light- and medium-mass nuclei
R. Schiavilla · L. Girlanda · A. Gnech · A. Kievsky · A. Lovato · L.E. Marcucci · M. Piarulli · M. Viviani
Classes of two-nucleon ( $2 N$ ) contact interactions are developed in configuration space at leading order (LO), next-to-leading order (NLO), and next-to-next-to-next-to-leading order (N3LO) by fitting the experimental singlet $n p$ scattering length and deuteron binding energy at LO, and $n p$ and $pp$ scattering data in the laboratory-energy range 0--15 MeV at NLO and 0--25 MeV at N3LO. These interactions are regularized by including two Gaussian cutoffs, one for $T$ = $0$ and the other for $T$ = $1$ channels. The cutoffs are taken to vary in the ranges $R_{0}$ = $(1.5$ --2.3) fm and $R_{1}$ = $(1.5$ --3.0) fm. The 780 (1,100) data points up to 15 (25) MeV energy, primarily differential cross sections, are fitted by the NLO (N3LO) models with a $χ^{2}$ /datum about 1.7 or less (well below 1.5), when harder cutoff values are adopted. As a first application, we report results for the binding energies of nuclei with mass numbers $A$ = $3$ --6 and 16 obtained with selected LO and NLO $2 N$ models both by themselves as well as in combination with a LO three-nucleon ( $3 N$ ) contact interaction. The latter is characterized by a single low-energy constant that is fixed to reproduce the experimental $^{3}$ H binding energy. The inclusion of the $3 N$ interaction largely removes the sensitivity to cutoff variations in the few-nucleon systems and leads to predictions for the $^{3}$ He and $^{4}$ He binding energies that cluster around 7.8 MeV and 30 MeV, respectively. However, in $^{16}$ O this cutoff sensitivity remains rather strong. Finally, predictions at LO only are also reported for medium-mass nuclei with $A$ = $40$ , 48, and 90.
nucl-thPRC(2021)·41 citations
03
Microscopic Calculation of Fission Product Yields with Particle Number Projection
Marc Verriere🇺🇸 · David Regnier🇺🇸 · Nicolas Schunck🇫🇷
Fission fragments' charge and mass distribution is an important input to applications ranging from basic science to energy production or nuclear non-proliferation. In simulations of nucleosynthesis or calculations of superheavy elements, these quantities must be computed from models, as they are needed in nuclei where no experimental information is available. Until now, standard techniques to estimate these distributions were not capable of accounting for fine-structure effects, such as the odd-even staggering of the charge distributions. In this work, we combine a fully-microscopic collective model of fission dynamics with a recent extension of the particle number projection formalism to provide the highest-fidelity prediction of the primary fission fragment distributions for the neutron-induced fission of $^{235}$ U and $^{239}$ Pu. We show that particle number projection is an essential ingredient to reproduce odd-even staggering in the charge yields and benchmark the performance of various empirical probability laws that could simulate its effect. This new approach also enables for the first time the realistic determination of two-dimensional isotopic yields within nuclear density functional theory.
nucl-thPRC(2021)·40 citations
04
Entrainment effects in neutron-proton mixtures within the nuclear-energy density functional theory. I. Low-temperature limit
Nicolas Chamel · Valentin Allard
Mutual entrainment effects in cold neutron-proton mixtures are studied in the framework of the self-consistent nuclear energy-density functional theory. Exact expressions for the mass currents, valid for both homogeneous and inhomogeneous systems, are directly derived from the time-dependent Hartree-Fock equations with no further approximation. The equivalence with the Fermi-liquid expression is also demonstrated. Focusing on neutron-star cores, a convenient and simple analytical formulation of the entrainment matrix in terms of the isovector effective mass is found, thus allowing to relate entrainment phenomena in neutron stars to isovector giant dipole resonances in finite nuclei. Results obtained with different functionals are presented. These include the Brussels-Montreal functionals, for which unified equations of state of neutron stars have been recently calculated.
nucl-thastro-ph.HEPRC(2019)·17 citations
05
Selfinteracting Particle-Antiparticle System of Bosons
D. Anchishkin🇺🇦 · V. Gnatovskyy🇺🇦 · D. Zhuravel🇺🇦 · V. Karpenko🇺🇦
Thermodynamic properties of a system of interacting boson particles and antiparticles at finite temperatures are studied within the framework of the thermodynamically consistent Skyrme-like mean-field model. The mean field contains both attractive and repulsive terms. Self-consistency relations between the mean field and thermodynamic functions are derived. We assume conservation of the isospin density for all temperatures. It is shown that, independently of the strength of the attractive mean field, at the critical temperature $T_{c}$ the system undergoes the phase transition of second-order to the Bose-Einstein condensate, which exists in the temperature interval $0 \leq T \leq T_{c}$ . We obtained that the condensation represents a discontinuity of the derivative of the heat capacity at $T = T_{c}$ , and condensate occurs only for the component with a higher particle-number density in the particle-antiparticle system.
nucl-thhep-phquant-phPRC(2022)·6 citations
06
Normalizing flows for microscopic many-body calculations: an application to the nuclear equation of state
Jack Brady · Pengsheng Wen · Jeremy W. Holt
Normalizing flows are a class of machine learning models used to construct a complex distribution through a bijective mapping of a simple base distribution. We demonstrate that normalizing flows are particularly well suited as a Monte Carlo integration framework for quantum many-body calculations that require the repeated evaluation of high-dimensional integrals across smoothly varying integrands and integration regions. As an example, we consider the finite-temperature nuclear equation of state. An important advantage of normalizing flows is the ability to build highly expressive models of the target integrand, which we demonstrate enables precise evaluations of the nuclear free energy and its derivatives. Furthermore, we show that a normalizing flow model trained on one target integrand can be used to efficiently calculate related integrals when the temperature, density, or nuclear force is varied. This work will support future efforts to build microscopic equations of state for numerical simulations of supernovae and neutron star mergers that employ state-of-the-art nuclear forces and many-body methods.
nucl-thPRL(2021)·10 citations
07
Tight multi-messenger constraints on the neutron star equation of state from GW170817 and a forward model for kilonova light curve synthesis
Matt Nicholl🇬🇧 · Ben Margalit🇺🇸 · Patricia Schmidt🇬🇧 · Graham P. Smith🇬🇧 · Evan J. Ridley🇬🇧 · James Nuttall🇬🇧
We present a rapid analytic framework for predicting kilonova light curves following neutron star (NS) mergers, where the main input parameters are binary-based properties measurable by gravitational wave detectors (chirp mass and mass ratio, orbital inclination) and properties dependent on the nuclear equation of state (tidal deformability, maximum NS mass). This enables synthesis of a kilonova sample for any NS source population, or determination of the observing depth needed to detect a live kilonova given gravitational wave source parameters in low latency. We validate this code, implemented in the public MOSFiT package, by fitting it to GW170817. A Bayes factor analysis overwhelmingly ( $B > 1 0^{10}$ ) favours the inclusion of an additional luminosity source in addition to lanthanide-poor dynamical ejecta during the first day. This is well fit by a shock-heated cocoon model, though differences in the ejecta structure, opacity or nuclear heating rate cannot be ruled out as alternatives. The emission thereafter is dominated by a lanthanide-rich viscous wind. We find the mass ratio of the binary is $q = 0.92 \pm 0.07$ (90% credible interval). We place tight constraints on the maximum stable NS mass, $M_{TOV} = 2.1 7_{- 0.11}^{+ 0.08}$ M $_{⊙}$ . For a uniform prior in tidal deformability, the radius of a 1.4 M $_{⊙}$ NS is $R_{1.4} \sim 10.7$ km. Re-weighting with a prior based on equations of state that support our credible range in $M_{TOV}$ , we derive a final measurement $R_{1.4} = 11.0 6_{- 0.98}^{+ 1.01}$ km. Applying our code to the second gravitationally-detected neutron star merger, GW190425, we estimate that an associated kilonova would have been fainter (by $\sim 0.7$ mag at one day post-merger) and declined faster than GW170817, underlining the importance of tuning follow-up strategies individually for each GW-detected NS merger.
↳ astro-ph.HEastro-ph.SRgr-qcnucl-thMNRAS(2021)·108 citations
08
Phase diagram of interacting pion matter and isospin charge fluctuations
O. S. Stashko🇺🇦 · O. V. Savchuk🇩🇪 · R. V. Poberezhnyuk🇺🇦 · V. Vovchenko🇺🇸 · M. I. Gorenstein🇺🇸
Equation of state and electric (isospin) charge fluctuations are studied for matter composed of interacting pions. The pion matter is described by self interacting scalar fields via a $ϕ^{4} - ϕ^{6}$ type Lagrangian. The mean-field approximation is used, and interaction parameters are fixed by fitting lattice QCD results on the isospin density as a function of the isospin chemical potential at zero temperature. Two scenarios for fixing the model parameters -- with and without the first order phase transition -- are considered, both yielding a satisfactory description of the lattice data. Thermodynamic functions and isospin charge fluctuations are studied and systematically compared for these two scenarios, yielding qualitative differences in the behavior of isospin charge susceptibilities. These differences can be probed by lattice simulations at temperatures $T ≲ 100$ MeV.
↳ hep-phnucl-thPRC(2021)·4 citations
09
Unperturbed inverse kinematics nucleon knockout measurements with a 48 GeV/c carbon beam
M. Patsyuk · J. Kahlbow · G. Laskaris · M. Duer · V. Lenivenko · E.P. Segarra · T. Atovullaev · G. Johansson · T. Aumann · A. Corsi · O. Hen · M. Kapishin and 157 other authors
From superconductors to atomic nuclei, strongly-interacting many-body systems are ubiquitous in nature. Measuring the microscopic structure of such systems is a formidable challenge, often met by particle knockout scattering experiments. While such measurements are fundamental for mapping the structure of atomic nuclei, their interpretation is often challenged by quantum mechanical initial- and final-state interactions (ISI/FSI) of the incoming and scattered particles. Here we overcome this fundamental limitation by measuring the quasi-free scattering of 48 GeV/c 12C ions from hydrogen. The distribution of single protons is studied by detecting two protons at large angles in coincidence with an intact 11B nucleus. The 11B detection is shown to select the transparent part of the reaction and exclude the otherwise large ISI/FSI that would break the 11B apart. By further detecting residual 10B and 10Be nuclei, we also identified short-range correlated (SRC) nucleon-nucleon pairs, and provide direct experimental evidence for the separation of the pair wave-function from that of the residual many-body nuclear system. All measured reactions are well described by theoretical calculations that do not contain ISI/FSI distortions. Our results thus showcase a new ability to study the short-distance structure of short-lived radioactive atomic nuclei at the forthcoming FAIR and FRIB facilities. These studies will be pivotal for developing a ground-breaking microscopic understanding of the structure and properties of nuclei far from stability and the formation of visible matter in the universe.
↳ nucl-exnucl-thNat.Phys.(2021)·67 citations
10
Resonance suppression of the r-mode instability in superfluid neutron stars: Accounting for muons and entrainment
Elena M. Kantor🇷🇺 · Mikhail E. Gusakov🇷🇺 · Vasiliy A. Dommes🇷🇺
We calculate the finite-temperature r-mode spectrum of a superfluid neutron star accounting for both muons in the core and the entrainment between neutrons and protons. We show that the standard perturbation scheme, considering the rotation rate as an expansion parameter, breaks down in this case. We develop an original perturbation scheme which circumvents this problem by treating both the perturbations due to rotation and (weak) entrainment simultaneously. Applying this scheme, we propose a simple method for calculating the superfluid r-mode eigenfrequency in the limit of vanishing rotation rate. We also calculate the r-mode spectrum at finite rotation rate for realistic microphysics input (adopting, however, the Newtonian framework and Cowling approximation when considering perturbed oscillation equations) and show that the normal r-mode exhibits resonances with superfluid r-modes at certain values of temperatures and rotation frequencies in the parameter range relevant to neutron stars in low-mass X-ray binaries (LMXBs). This turns the recently suggested phenomenological model of resonance r-mode stabilization into a quantitative theory, capable of explaining observations. A strong dependence of resonance rotation rates and temperatures on the neutron superfluidity model allows us to constrain the latter by confronting our calculations with the observations of neutron stars in LMXBs.
↳ astro-ph.HEgr-qcnucl-thPRD(2021)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE