Nuclear Theory·nucl-th

Monday·July 29, 2024

6 papers—5 primary·1 cross-listed

01
Deformed natural orbitals for ab initio calculations
Alberto Scalesi🇫🇷 · Thomas Duguet🇫🇷 · Mikael Frosini🇫🇷 · Vittorio Somà🇫🇷
The rapid development of ab initio nuclear structure methods towards doubly open-shell nuclei, heavy nuclei and greater accuracy occurs at the price of evermore increased computational costs, especially RAM and CPU time. While most of the numerical simulations are carried out by expanding relevant operators and wave functions on the spherical harmonic oscillator basis, alternative one-body bases offering advantages in terms of computational efficiency have recently been investigated. In particular, the so-called natural basis used in combination with symmetry-conserving methods applicable to doubly closed-shell nuclei has proven beneficial in this respect. The present work examines the performance of the natural basis in the context of symmetry-breaking many-body calculations enabling the description of superfluid and deformed open-shell nuclei at polynomial cost with system's size. First, it is demonstrated that the advantage observed for closed-shell nuclei carries over to open-shell ones. A detailed investigation of natural-orbital wave functions provides useful insight to support this finding and to explain the superiority of the natural basis over alternative ones. Second, it is shown that the use of natural orbitals combined with importance-truncation techniques leads to an even greater gain in terms of computational costs. The presents results pave the way for the systematic use of natural-orbital bases in future implementations of non-perturbative many-body methods.
nucl-thEPJA(2025)·8 citations
02
Nambu-Jona-Lasinio description of hadronic matter from a Bayesian approach
K. D. Marquez🇵🇹 · Tuhin Malik🇵🇹 · Helena Pais🇵🇹 · Débora P. Menezes🇧🇷 · Constança Providência🇵🇹
A microscopic nuclear matter formalism with explicit chiral symmetry based on the Nambu Jona-Lasinio model is considered to describe nuclear matter. To reproduce nuclear matter properties adequately at the saturation density, four-point and eight-point interactions are introduced. Within a Bayesian inference approach, the parameters of the model are determined by imposing nuclear matter, both experimental and from {\it ab-initio} calculations, and neutron star observational constraints. Nuclear matter properties are well reproduced with an effective mass of 0.75 to 0.8 nucleon mass at the saturation density. At 90% confidence level, the radius of a $1.4 M_{⊙}$ star varies between 11.48 km and 13.20 km, masses as large as $\sim 2.2 M_{⊙}$ are predicted and the radius of a 2 M $_{⊙}$ star is above 10.5 km. High-density perturbative QCD (pQCD) results exclude equations of state that predict larger maximum masses and radii. The speed of sound increases monotonically with density and reaches values as large as $0.7 c$ - $0.8 c$ in the center of massive stars. Several properties such as the polytropic index or the renormalized trace anomaly, that have been proposed to identify the deconfined phase transition, are analyzed. Interestingly, the radius of the obtained posterior that also meets pQCD constraints aligns closely with the mass-radius measurement of the recent PSR J0437-4715, which contrasts with other relativistic mean field model results.
nucl-thastro-ph.HEhep-thPRD(2024)·14 citations
03
Influence of effective nucleon mass on equation of state for supernova simulations and neutron stars
Shuying Li · Junbo Pang · Hong Shen · Jinniu Hu · Kohsuke Sumiyoshi
We investigate the influence of the effective nucleon mass on the equation of state (EOS), which is constructed for simulations of core-collapse supernovae and binary neutron star mergers, within the relativistic mean-field (RMF) framework. The study introduces a new RMF parameter set, TM1m, which is a modification of the TM1e model with an adjusted effective mass, maintaining the saturation properties of nuclear matter. The TM1m model, with a larger effective mass ratio ( $M^{*} / M \sim 0.8$ ) compared to the TM1e model ( $M^{*} / M \sim 0.63$ ), is employed to construct a new EOS table, EOS5. This EOS table is designed to offer insights into the influence of the effective nucleon mass on the EOS within a relativistic framework, particularly above the saturation density. The results of EOS5 are compared with those obtained from other models, including both relativistic and nonrelativistic approaches. The properties of cold neutron stars, calculated using the TM1m model, are compatible with the existence of a $2 M_{⊙}$ pulsar and the latest constraints on the tidal deformability and radii of a canonical $1.4 M_{⊙}$ neutron star, derived from astrophysical observations.
nucl-thastro-ph.HEApJ(2025)·13 citations
04
Investigating the effect of nuclear deformation on $β$ -decay half-lives of neutron-rich nuclei
Jameel-Un Nabi · Tuncay Bayram · Wajeeha Khalid · Arslan Mehmood · Alper Köseoğlu
We examine the effect of nuclear deformation on the calculated $β$ -decay half-lives of 55 neutron-rich nuclei. The deformation values were computed using DD-PC1 and DD-ME2 interactions in the Relativistic Hartree-Bogoliubov model. Yet another set of deformation was adopted from the Finite Range Droplet Model (FRDM). The model-dependent deformation values were used as a free parameter in the proton-neutron quasiparticle random phase approximation model to calculate the $β$ -decay properties under terrestrial and stellar conditions. The Gamow-Teller strength distributions, branching ratios, half-lives and stellar weak rates of selected nuclei were later investigated. It was concluded that the $β$ -decay properties of neutron-rich nuclei changed with nuclear deformation. The FRDM computed deformation values provided the best predictions for calculated half-lives followed by the DD-ME2 functional. The terrestrial $β$ -decay half-lives changed up to 3 orders of magnitude and the stellar $β$ -rates within a factor of 2 as the neutron-rich nuclei switched their geometrical configurations. For magic number nucleus $^{138}$ Sn, the stellar rates changed substantially by more than 1 order of magnitude as the nucleus transitioned away from the spherical shape. Our investigation might prove useful for a realistic modeling of nucleosynthesis calculation.
nucl-thastro-ph.SRBraz.J.Phys.(2026)·1 citation
05
Bulk viscosity of nuclear matter with pions in the neutrino-trapped regime
Steven P. Harris🇺🇸 · Bryce Fore🇺🇸 · Sanjay Reddy🇺🇸
Recent work [B. Fore and S. Reddy, Phys. Rev. C 101 035809 (2020)] has shown that the population of thermal pions could modify the equation of state and transport properties of hot and dense neutron-rich matter and introduce new reaction pathways to change the proton fraction. In this article we study their impact on the bulk viscosity of dense matter, focusing on the neutrino-trapped regime that would be realized in neutron star mergers and supernovae. We find that the presence of a thermal population of pions alters the bulk viscosity by modifying the EoS (via the susceptibilities) and by providing new reaction pathways to achieve beta-equilibrium. In neutron star merger conditions, the bulk viscosity in neutrino-trapped $n p e μ$ matter (without pions) has its peak at temperatures of at most a couple MeV and is quite small at temperatures of tens of MeV. We find that thermal pions enhance the low-temperature peak of the bulk viscosity by a factor of a few and shift it to slightly lower temperatures. At higher temperatures, where the pion abundance is large but the bulk viscosity is traditionally small, pions can increase the bulk viscosity by an order of magnitude or more, although it is still orders of magnitude smaller than its peak value.
nucl-thastro-ph.HEPRC(2025)·13 citations
06
Tetraquarks at large $M$ and large $N$
Héloïse Allaman🇨🇭 · Majid Ekhterachian🇨🇭 · Filippo Nardi🇨🇭 · Riccardo Rattazzi🇨🇭 · Stefan Stelzl🇨🇭
We study tetraquarks in large $N$ QCD with heavy quarks, in the domain where non-relativistic quantum mechanics offers an adequate approximation. Within the regime of validity of the Born-Oppenheimer approximation, we systematically study and explicitly construct tetraquark states. At leading order in the $1/ N$ expansion, the bound spectrum consists of free mesons, while the $1/ N$ corrections give rise to a Born-Oppenheimer potential that can bind the mesons into tetraquarks. We find two different types of tetraquarks, each endowed with distinct color-spatial wavefunctions. These states arise in the presence of an $O (N)$ mass hierarchy between the quarks and the antiquarks. We provide a quantitative argument indicating that only for such a hierarchy is the ground state of the system a tetraquark. We discuss what the extrapolation of our results to realistic values of the parameters may imply for the QCD tetraquark states.
↳ hep-phhep-thnucl-thJHEP(2024)·7 citations

Affiliations

first authorsco-authorsvia INSPIRE

Deformed natural orbitals for ab initio calculations

Nambu-Jona-Lasinio description of hadronic matter from a Bayesian approach

Influence of effective nucleon mass on equation of state for supernova simulations and neutron stars

Investigating the effect of nuclear deformation on β-decay half-lives of neutron-rich nuclei

Bulk viscosity of nuclear matter with pions in the neutrino-trapped regime

Tetraquarks at large M and large N

Affiliations

Investigating the effect of nuclear deformation on $β$ -decay half-lives of neutron-rich nuclei

Tetraquarks at large $M$ and large $N$