Nuclear Theory·nucl-th

Friday·February 23, 2024

18 papers—7 primary·11 cross-listed

01
Recent advances in chiral EFT based nuclear forces and their applications
Ruprecht Machleidt🇺🇸 · Francesca Sammarruca🇺🇸
During the past two decades, chiral effective field theory has evolved into a powerful tool to derive nuclear forces from first principles. Nearly all two-nucleon interactions have been worked out up to sixth order of chiral perturbation theory, while, with few exceptions, three-nucleon forces, which play a subtle, but crucial role in microscopic nuclear structure calculations, have been derived up to fifth order. We review the current status of these forces as well as their applications in nuclear many-body systems. While the ab initio description of light nuclei is generally very successful, we point out and analyze problems encountered with medium-mass nuclei. We also survey the construction of equations of state for symmetric nuclear matter and neutron-rich matter based on chiral forces. A focal point is the symmetry energy and its impact on neutron skins and systems of astrophysical relevance. The physics of neutron-rich systems, from nuclei to compact stars, is essentially determined by the density dependence of the symmetry energy. We review the status of predictions in comparison with latest empirical constraints, with particular attention to those extracted from parity violating electron scattering.
nucl-thPPNP(2024)·79 citations
02
Upper Bound on the Speed of Sound in Nuclear Matter from Transport
Mauricio Hippert🇺🇸 · Jorge Noronha🇺🇸 · Paul Romatschke🇺🇸
We point out that there is an upper bound on the speed of sound squared given by $c_{s}^{2} \leq 0.781$ valid for all known systems described by relativistic transient hydrodynamics where calculations of certain ratios of hydrodynamic transport coefficients can be performed from first principles. Assuming this bound is valid for ultradense matter implies that the maximum mass of isolated (non-rotating) neutron stars cannot be larger than 2.7 solar masses.
nucl-thastro-ph.HEhep-phPLB(2025)·27 citations
03
Fragmentation of the Giant Pairing Vibration in 14C induced by many-body processes
Francisco Barranco · Gregory Potel · Enrico Vigezzi
We present a theoretical framework for treating the full excitation spectrum of J{\pi} = 0+ pair addition modes, including the well-known low-lying and bound Pairing Vibration on par with the predicted Giant Pairing Vibration lying in the continuum. Our formalism includes the coupling to low-energy collective quadrupole modes of the core, in such a way that both single-particle self-energy effects and the pairing interaction induced by phonon exchange are accounted for. The theory is applied to the case of the excitation spectrum of 14C, recently populated by two-neutron transfer reactions.
nucl-thPRL(2025)·4 citations
04
Properties of H particle-admixed compact star
Xuhao Wu🇨🇳 · Liming Wang · Hong-Tao An · Min Ju🇨🇳 · Hong Shen🇨🇳
We explore the potential manifestation of a hexaquark, the H particle, as a constituent within neutron stars. The H particle, characterized by a quark composition of $uu dd ss$ , is constructed using the framework of Chromomagnetic Interaction (CMI). Specifically, we contemplate the flavor-singlet state H with $J^{P} = 0^{+}$ . Our computations indicate that the three-flavor hexaquark state, the H particle, possesses a lower mass of $2212.7 MeV$ in comparison to the $d^{*} (2380)$ , implying greater stability than the two-flavor $d^{*} (2380)$ . The analysis involving the H particle is carried out using the relativistic mean-field (RMF) model. We investigate the influence of H particle couplings, a key factor in determining the system stability, and focus on the potential existence of H particle within neutron stars. We find that H particle could potentially endure as a stable constituent within neutron stars, and lead to a reduction of the maximum mass.
nucl-thEPJC(2026)·3 citations
05
Bayesian Model Averaging (BMA) for nuclear data evaluation
E. Alhassan · D. Rochman · G. Schnabel · A.J. Koning
To ensure agreement between theoretical calculations and experimental data, parameters to selected nuclear physics models, are perturbed, and fine-tuned in nuclear data evaluations. This approach assumes that the chosen set of models accurately represents the `true' distribution. Furthermore, the models are chosen globally, indicating their applicability across the entire energy range of interest. However, this approach overlooks uncertainties inherent in the models themselves. As a result, achieving satisfactory fits to experimental data within certain energy regions for specific channels becomes challenging, as the evaluation is constrained by the deficiencies of the selected models. In this work, we propose that instead of selecting globally a winning model set and proceeding with it as if it was the `true' model set, we instead, take a weighted average over multiple models within a BMA framework, each weighted by its posterior probability. The method involves executing a set of TALYS calculations by randomly varying multiple nuclear physics models and their parameters to yield a vector of calculated observables. Next, the likelihood function was computed at each considered incident energy point for selected cross sections by comparing the vector of calculated observables with that of the selected differential experimental data. As the cross sections and elastic angular distributions were updated locally on a per-energy-point basis, the approach typically results in discontinuities or "kinks" in the curves, and these were addressed using spline interpolation. The proposed BMA method was applied to the evaluation of proton induced reactions on $^{58}$ Ni within 1 - 100 MeV. The results demonstrate favorable comparisons with experimental data, as well as with the TENDL-2021 evaluation.
nucl-thNucl.Sci.Tech.(2024)·8 citations
06
Estimating angular momenta of fission fragments from isomeric yield ratios
Zhihao Gao · Andreas Solders · Ali Al-Adili · Simone Cannarozzo · Mattias Lantz · Stephan Pomp
Purpose: To deduce the angular momenta of fission fragments based on the observed isomeric yield ratios (IYR) in 25-MeV proton-induced fission of 238U and to compare these using Wilson's model. Method: A surrogate model of GEF has been developed to generate properties of primary fission fragments. Based on the excitation energy and angular momentum of fission fragments from GEF, an energy versus angular momentum matrix is reconstructed using a set of parameters. With such matrices as input, TALYS is used to calculate the de-excitation of the fission fragments, from which the IYRs are obtained. By varying one of the parameters, the root-mean-square angular momentum (Jrms), which determines the angular momentum distribution of the matrix, Jrms-dependent IYRs are obtained. Considering all primary fission fragments contributing to the IYR for a given fission product, the average angular momentum of those fragments is estimated. Results: Data of 31 IYRs in proton-induced fission of 238U were analysed. As a result, the average Jrms, equivalent to average angular momentum Jav, with uncertainties of 24 fission products, are presented. Considering the neutron emissions of the primary fission fragments, the Jav as a function of the primary fission fragment is presented. A mass dependency of Jav is observed in the proton-induced fission of 238U. Moreover, the Jav for A larger than 131 could be described by the parameterisation proposed by J. Wilson. In general, higher Jav are observed in the present work compared to those from Wilson et al. This is likely due to the higher excitation energy of the fissioning nuclei in this work compared to Wilson's. Furthermore, systematic measurements of the Jav of fission products in the symmetric mass region are presented for the first time. A decreasing trend with mass numbers is observed, which can not be explained by the proposal in Wilson's paper.
nucl-thPRC(2024)·4 citations
07
Bayesian inference of thermal effects in dense matter within the covariant density functional theory
Adriana R. Raduta🇷🇴 · Mikhail V. Beznogov🇷🇴 · Micaela Oertel🇫🇷
The high temperatures reached in a proto-neutron star or during the post-merger phase of a binary neutron star coalescence lead to non-negligible thermal effects on the equation of state (EOS) of dense nuclear matter. Here we study these effects within the covariant density functional theory employing the posteriors of a Bayesian inference, which encompasses a large sample of EOS models. Different densities and temperatures are considered. We find that for a number of quantities thermal effects are strongly correlated with the Dirac effective mass ( $m^{*}$ ) of the nucleons and/or its logarithmic derivative as a function of density. These results can be explained within the low temperature approximation though they survive beyond this limit.
nucl-thPLB(2024)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE

Recent advances in chiral EFT based nuclear forces and their applications

Upper Bound on the Speed of Sound in Nuclear Matter from Transport

Fragmentation of the Giant Pairing Vibration in 14C induced by many-body processes

Properties of H particle-admixed compact star

Bayesian Model Averaging (BMA) for nuclear data evaluation

Estimating angular momenta of fission fragments from isomeric yield ratios

Bayesian inference of thermal effects in dense matter within the covariant density functional theory

Affiliations