Nuclear Theory·nucl-th

Friday·July 1, 2022

16 papers—10 primary·6 cross-listed

01
Applications of reduced basis methods to the nuclear single particle spectrum
Amy L. Anderson · Graham L. O'Donnell · J. Piekarewicz
Reduced basis methods provide a powerful framework for building efficient and accurate emulators. Although widely applied in many fields to simplify complex models, reduced basis methods have only been recently introduced into nuclear physics. In this letter we build an emulator to study the single-particle structure of atomic nuclei. By scaling a suitable mean-field Hamiltonian, a "universal" reduced basis is constructed capable of accurately and efficiently reproduce the entire single-particle spectrum of a variety of nuclei. Indeed, the reduced basis model reproduces both ground- and excited-state energies as well as the associated wave-functions with remarkable accuracy. Our results bode well for more demanding applications that use Bayesian optimization to calibrate nuclear energy density functionals.
nucl-thnucl-exPRC(2022)·17 citations
02
Uncertainty quantification of transition operators in the empirical shell model
Jordan M. R. Fox · Calvin W. Johnson · Rodrigo Navarro Perez
While empirical shell model calculations have successfully described low-lying nuclear data for decades, only recently has significant effort been made to quantify the uncertainty in such calculations. Here we quantify the statistical error in effective parameters for transition operators in empirical calculations in the $s d$ ( $1 s_{1/2}$ - $0 d_{3/2}$ - $0 d_{5/2}$ ) valence space, specifically the quenching of Gamow-Teller transitions, effective charges for electric quadrupole (E2) transitions, and the effective orbital and spin couplings for magnetic dipole (M1) transitions. We find the quenching factor for Gamow-Teller transitions relative to free-space values is tightly constrained and that the isoscalar coupling of E2 is much more tightly constrained than the isovector coupling. For effective M1 couplings, we found isovector components more constrained than isoscalar, but that to get any sensible result we had to fix one of four couplings. This detailed quantification of uncertainties, while highly empirical, nonetheless is an important step towards interpretation of experiments.
nucl-thnucl-exPRC(2023)·4 citations
03
Equation of State at High-Baryon Density and Compact Stellar Objects
Veronica Dexheimer🇺🇸
In this contribution I review the connection between compact stars and high-baryon density matter, focusing on astrophysical observables for deconfinement to quark matter. I discuss modern ingredients, repositories, and constraints for the neutron-star equations of state. Finally, I draw comparisons between dense and hot matter created in neutron-star mergers and heavy-ion collisions, and the possibility of quantitatively establishing a link between them.
nucl-thastro-ph.HEastro-ph.SRhep-phActa Phys.Polon.Supp.(2023)·0 citations
04
Radiative neutron capture reaction rates for r-process nucleosynthesis
Vinay Singh · Joydev Lahiri · Malay Kanti Dey · D. N. Basu
About half of the elements beyond iron are synthesized in stars by rapid-neutron capture process (r-process). The stellar environment provides very high neutron flux in a short time ( $\sim$ seconds) which is conducive for the creation of progressively neutron-rich nuclei till the waiting point is reached after which no further neutron capture reactions proceed. At this point such extremely neutron-rich nuclei become stable via $β^{-}$ decay. A detailed understanding of the r-process remains illusive. In the present work, we explore the radiative neutron-capture (n, $γ$ ) cross sections and reaction rates around the r-process peak near mass number eighty. The inherent uncertainties remain large in some cases, particularly in case of neutron-rich nuclei. When the low-energy enhancement exists, it results in significant increase in the reaction rate for neutron-capture.
nucl-thastro-ph.SRnucl-exPramana(2023)·0 citations
05
Sub-barrier fusion hindrance and absence of neutron transfer channels
Vinay Singh · Joydev Lahiri · Partha Roy Chowdhury · D. N. Basu
The sub-barrier fusion hindrance has been observed in the domain of very low energies of astrophysical relevance. This phenomenon can be analyzed effectively using an uncomplicated straightforward elegant mathematical formula gleaned presuming diffused barrier with a Gaussian distribution. The mathematical formula for cross section of nuclear fusion reaction has been obtained by folding together a Gaussian function representing the fusion barrier height distribution and the expression for classical cross section of fusion assuming a fixed barrier. The variation of fusion cross section as a function of energy, thus obtained, describes well the existing data on sub-barrier heavy-ion fusion for lighter systems of astrophysical interest. Employing this elegant formula, cross sections of interacting nuclei from $^{16}$ O + $^{18}$ O to $^{12}$ C + $^{198}$ Pt, all of which were measured down to $<$ 10 $μ$ b have been analyzed. The agreement of the present analysis with the measured values is comparable, if not better, than those calculated from more sophisticated calculations. The three parameters of this formula varies rather smoothly implying its usage in estimating the excitation function or extrapolating cross sections for pairs of interacting nuclei which are yet to be measured. Possible effects of neutron transfers on the hindrance in heavy-ion fusion have been explored.
nucl-thastro-ph.SRnucl-exIndian J.Phys.(2023)·0 citations
06
Effect of short- and long-range correlations on neutron skins of various neutron-rich doubly magic nuclei
G. Co' · M. Anguiano · A. M. Lallena
We study the effects of correlations beyond the independent particle model in the evaluation of neutron skins of various neutron-rich doubly magic nuclei. We consider short- and long-range correlations to take into account the presence of the strongly repulsive core of the bare nucleon-nucleon interaction and collective nuclear phenomena, respectively. Despite the strong sensitivity on the structure of the nucleus considered, our results indicate that, in general, correlations increase the values of the neutron skins.
nucl-thPRC(2022)·0 citations
07
Calculation of the Thomas-Ehrman shift in $^{16}$ F and $^{15}$ O(p,p) cross section with the Gamow shell model
N. Michel · J. G. Li · L. H. Ru · W. Zuo
The $^{16}$ F nucleus is situated at the proton drip-line and is unbound by proton emission by only about 500 keV. Continuum coupling is then prominent in this nucleus. Added to that, its low-lying spectrum consists of narrow proton resonances as well. It is then a very good candidate to study nuclear structure and reactions at proton drip-line. The low-lying spectrum and scattering proton-proton cross section of $^{16}$ F have then been calculated with the coupled-channel Gamow shell model framework for that matter using an effective Hamiltonian. Experimental data are very well reproduced, as well as in its mirror nucleus $^{16}$ N. Isospin-symmetry breaking generated by the Coulomb interaction and continuum coupling explicitly appears in our calculations. In particular, the different continuum couplings in $^{16}$ F and $^{16}$ N involving $s_{1/2}$ partial waves allow to explain the different ordering of low-lying states in their spectrum.
nucl-thPRC(2022)·17 citations
08
Effect of configuration mixing on quadrupole and octupole collective states of transitional nuclei
Kosuke Nomura
A model is presented that simultaneously describes shape coexistence and quadrupole and octupole collective excitations within a theoretical framework based on the nuclear density functional theory and the interacting boson model. An optimal interacting-boson Hamiltonian that incorporates the configuration mixing between normal and intruder states, as well as the octupole degrees of freedom, is identified by means of self-consistent mean-field calculations using a universal energy density functional and a pairing interaction, with constraints on the triaxial quadrupole and the axially-symmetric quadrupole and octupole shape degrees of freedom. An illustrative application to the transitional nuclei $^{72}$ Ge, $^{74}$ Se, $^{74}$ Kr, and $^{76}$ Kr shows that the inclusion of the intruder states and the configuration mixing significantly lower the energy levels of the excited $0^{+}$ states, and that the predicted low-lying positive-parity states are characterized by the strong admixture of nearly spherical, weakly deformed oblate, and strongly deformed prolate shapes. The low-lying negative-parity states are shown to be dominated by the deformed intruder configurations.
nucl-thnucl-exPRC(2022)·10 citations
09
Equation of State of Neutron-Rich Matter in $d$ -Dimensions
Bao-Jun Cai🇨🇳 · Bao-An Li🇺🇸
Nuclear systems under constraints, with high degrees of symmetries and/or collectivities may be considered as moving effectively in spaces with reduced spatial dimensions. We first derive analytical expressions for the nucleon specific energy $E_{0} (ρ)$ , pressure $P_{0} (ρ)$ , incompressibility coefficient $K_{0} (ρ)$ and skewness coefficient $J_{0} (ρ)$ of symmetric nucleonic matter (SNM), the quadratic symmetry energy $E_{sym} (ρ)$ , its slope parameter $L (ρ)$ and curvature coefficient $K_{sym} (ρ)$ as well as the fourth-order symmetry energy $E_{sym, 4} (ρ)$ of neutron-rich matter in general $d$ spatial dimensions (abbreviated as " $d$ D") in terms of the isoscalar and isovector parts of the isospin-dependent single-nucleon potential according to the generalized Hugenholtz-Van Hove (HVH) theorem. The equation of state (EOS) of nuclear matter in $d$ D can be linked to that in the conventional 3-dimensional (3D) space by the $ϵ$ -expansion which is a perturbative approach successfully used previously in treating second-order phase transitions and related critical phenomena and more recently in studying the EOS of cold atoms. The $ϵ$ -expansion of nuclear EOS in $d$ D based on a reference dimension $d_{f} = d - ϵ$ is shown to be effective with $- 1 ≲ ϵ ≲ 1$ starting from $1 ≲ d_{f} ≲ 3$ in comparison with the exact expressions derived using the HVH theorem. Moreover, the EOS of SNM (with/without considering its potential part) is found to be reduced (enhanced) in lower (higher) dimensions, indicating in particular that the many-nucleon system tends to be deeper bounded but saturate at higher densities in spaces with lower dimensions. The links between the EOSs in 3D and $d$ D spaces from the $ϵ$ -expansion provide new perspectives to the EOS of neutron-rich matter.
nucl-thastro-ph.HEnucl-exAnnals Phys.(2022)·13 citations
10
Inferring the nuclear symmetry energy at supra saturation density from neutrino cooling
Tuhin Malik · B. K. Agrawal · Constança Providência
An ambitious goal of the astrophysical community is not only to constrain the equation of state (EOS) of neutron star (NS) matter by confronting it with astrophysics observations, but ultimately also to infer the NS composition. Nevertheless, the composition of the NS core is likely to remain uncertain unless we have an accurate determination of the nuclear symmetry energy at supra saturation density ( $ρ > ρ_{0}$ ). We investigate how the nucleonic direct Urca (dUrca) processes can be used as an effective probe to constraint the high density nuclear symmetry energy. A large number of minimally constrained EOSs has been constructed by applying a Bayesian approach to study the correlations of the symmetry energy at different densities with a few selected properties of a NS. The nuclear symmetry energy above the baryon density 0.5 fm $^{- 3}$ ( $\sim 3 ρ_{0}$ ) is found to be strongly correlated with NS mass at which the onset of nucleonic dUrca neutrino cooling takes place in the core. This allows us to constrain the high density behavior of nuclear symmetry energy within narrow bounds. {The pure neutron matter pressure constraint from chiral effective field theory rules out the onset of nucleonic dUrca in stars with a mass $≲$ 1.4 $M_{⊙}$ .} The onset of dUrca inside 1.6 M $_{⊙}$ to 1.8 M $_{⊙}$ NS implies a slope of the symmetry energy $L$ at $\sim 2.5 ρ_{0}$ , respectively, between 54 and 48 MeV.
nucl-thastro-ph.HEPRC(2022)·23 citations

Affiliations

first authorsco-authorsvia INSPIRE