Nuclear Theory·nucl-th

Tuesday·October 13, 2020

15 papers—9 primary·6 cross-listed

01
[Submitted on 9 Oct 2020]
Impact of Three-Body Forces on Elastic Nucleon-Nucleus Scattering Observables
Matteo Vorabbi🇺🇸 · Michael Gennari🇨🇦 · Paolo Finelli🇮🇹 · Carlotta Giusti🇮🇹 · Peter Navrátil🇨🇦 · Ruprecht Machleidt🇺🇸
In a previous series of papers we investigated the domain of applicability of chiral potentials to the construction of a microscopic optical potential (OP) for elastic nucleon-nucleus scattering. The final expression of the OP was a folding integral between the nucleon-nucleon ( $N N$ ) $t$ matrix and the nuclear density of the target. In these calculations $N N$ and three-nucleon ( $3 N$ ) chiral interactions were used for the target density and only the $N N$ interaction for the $N N$ $t$ matrix. The purpose of this work is to achieve another step towards the calculation of a more consistent OP introducing the $3 N$ force also in the dynamic part of the OP. In the present work this is approximated with a density dependent $N N$ interaction obtained after the averaging over the Fermi sphere. In practice, in our model the $3 N$ force acts as a medium correction of the bare $N N$ interaction used to calculate the $N N$ $t$ matrix. Even if the $3 N$ force is treated in an approximate way, this method naturally extends our previous model of the OP and allows a direct comparison of our present and previous results. We consider as case studies the elastic scattering of nucleons off $^{12}$ C and $^{16}$ O. We present results for the differential cross section and the spin observables for different values of the projectile energy. From the comparison with the experimental data and with the results of our previous model we assess the importance of the $3 N$ interaction in the dynamic part of the OP. Our analysis indicates that the contribution of the $3 N$ force in the $t$ matrix is small for the differential cross section and it is sizable for the spin observables, in particular, for the analyzing power. A chiral expansion order-by-order analysis of the scattering observables confirms the convergence of our results at the next-to-next-to-next-to-leading-order, as already established in our previous work.
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2010.04792 [pdf]
PRC(2021)·19 citations
02
[Submitted on 10 Oct 2020]
Electroweak decay of quark matter within dense astrophysical combustion flames
J. A. Rosero-Gil🇧🇷 · G. Lugones🇧🇷
We study the weak interaction processes taking place within a combustion flame that converts dense hadronic matter into quark matter in a compact star. Using the Boltzmann equation we follow the evolution of a small element of just deconfined quark matter all along the flame interior until it reaches chemical equilibrium at the back boundary of the flame. We obtain the reaction rates and neutrino emissivities of all the relevant weak interaction processes without making any assumption about the neutrino degeneracy. We analyse systematically the role the initial conditions of unburnt hadronic matter, such as density, temperature, neutrino trapping and composition, focusing on typical astrophysical scenarios such as cold neutron stars, protoneutron stars, and post merger compact objects. We find that the temperature within the flame rises significantly in a timescale of 1 nanosecond. The increase in $T$ strongly depends on the initial strangeness of hadronic matter and tends to be more drastic at larger densities. Typical final values range between $20$ and $60 MeV$ . The nonleptonic process $u + d \to u + s$ is always dominant in cold stars, but in hot objects the process $u + e^{-} \leftrightarrow d + ν_{e}$ becomes relevant, and in some cases dominant, near chemical equilibrium. The rates for the other processes are orders of magnitude smaller. We find that the neutrino emissivity per baryon is very large, leading to a total energy release per baryon of $2 - 60 MeV$ in the form of neutrinos along the flame. We discuss some astrophysical consequences of the results.
Comments:
19 pages, 16 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2010.04861 [pdf]
PRC(2021)·1 citation
03
[Submitted on 10 Oct 2020]
Hypertriton states from inverse scattering theory
Emile Meoto🇿🇦 · Mantile Lekala🇿🇦
The primary goal of this paper is to demonstrate that inverse scattering theory is a viable method for the simulation of lambda-nucleon potentials in hypernuclear few-body studies. To this end, we investigate the hypertriton, modelled as a $Λ n p$ three-body system in the $J^{π} = 1/ 2^{+}$ and $3/ 2^{+}$ channels. This three-body problem is solved using a hyperspherical-harmonic expansion of the Faddeev equations. The $Λ p$ and $Λ n$ interactions are modelled by the GLM-YN0 potentials. These simulated potentials were recovered through Gel'fand--Levitan--Marchenko inverse scattering theory as phase-equivalent simulations of the NSC97f meson-exchange model. The neutron-proton interaction is described by the semi-realistic Malfliet--Tjon I/III potential, with both singlet and triplet channels retained. For the ground state ( $J^{π} = 1/ 2^{+}$ ), we obtain a binding energy of $- 2.335$ ~MeV, corresponding to a $Λ$ separation energy of $B_{Λ} = + 0.104$ ~MeV relative to the $Λ + d$ breakup threshold. This value is comparable to those from lambda-nucleon potentials that are simulated through G-matrix methods. The excited $J^{π} = 3/ 2^{+}$ state is found to have a lambda separation energy of $B_{Λ} = - 1.444$ ~MeV relative to the $Λ + d$ breakup threshold, confirming that there is no bound excited hypertriton state.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2010.05070 [pdf]
1 citation
04
[Submitted on 11 Oct 2020]
Two-proton radioactivity within a generalized liquid drop model
J. P. Cui · Y. H. Gao · Y. Z. Wang · J. Z. Gu
The generalized liquid drop model (GLDM) is firstly extended to study the two-proton ( $2 p$ ) radioactivity half-lives of the ground-state of nuclei. According to the comparison between the calculated half-lives and the experimental data, it is shown that the GLDM describes the $2 p$ radioactivity half-lives well. In addition, by comparing its accuracy with other models, it is found that the GLDM has a comparable accuracy with them. Finally, the $2 p$ radioactivity half-lives of some most probable candidates are predicted with the GLDM by inputting the \textit{Q} $_{2 p}$ values (the released energy of the $2 p$ radioactivity) from the updated AME 2016 Mass Table, which may be useful for future experiments.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2010.05157 [pdf]
PRC(2020)·50 citations
05
[Submitted on 11 Oct 2020]
Reaction rate weighted multilayer nuclear reaction network
H. L. Liu · D. D. Han · P. Ji · Y. G. Ma
Nuclear reaction rate ( $λ$ ) is a significant factor in the process of nucleosynthesis. A multi-layer directed-weighted nuclear reaction network in which the reaction rate as the weight, and neutron, proton, $^{4}$ He and the remainder nuclei as the criterion for different reaction-layers is for the first time built based on all thermonuclear reactions in the JINA REACLIB database. Our results show that with the increase of the stellar temperature ( $T_{9}$ ), the distribution of nuclear reaction rates on the $R$ -layer network demonstrates a transition from unimodal to bimodal distributions. Nuclei on the $R$ -layer in the region of $λ = [1, 2.5 \times 1 0^{1}]$ have a more complicated out-going degree distribution than the one in the region of $λ = [1 0^{11}, 1 0^{13}]$ , and the number of involved nuclei at $T_{9} = 1$ is very different from the one at $T_{9} = 3$ . The redundant nuclei in the region of $λ = [1, 2.5 \times 1 0^{1}]$ at $T_{9} = 3$ prefer $(γ, p)$ and $(γ, α)$ reactions to the ones at $T_{9} = 1$ , which produce nuclei around the $β$ stable line. This work offers a novel way to the big-data analysis on nuclear reaction network at stellar temperatures.
Comments:
6 pages, 4 figures, 2 tables
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2010.05257 [pdf]
Chin.Phys.Lett.(2020)·5 citations
06
[Submitted on 11 Oct 2020]
Azimuthal anisotropy and multiplicities of hard photons and free nucleons in intermediate-energy heavy-ion collisions
S. S. Wang🇨🇳 · Y. G. Ma🇨🇳 · X. G. Cao🇨🇳 · D. Q. Fang🇨🇳 · C. W. Ma🇨🇳
Anisotropic flow can offer significant information of evolution dynamics in heavy-ion collisions. A systematic study of the directed flow $v_{1}$ and elliptic flow $v_{2}$ of hard photons and free nucleons is performed for $^{40}$ Ca+ $^{40}$ Ca collisions in a framework of isospin dependent quantum molecular dynamics (IQMD) model. The study firstly reveals that thermal photons emitted in intermediate-energy heavy-ion collisions have the behaviors of directed and elliptic flows. The interesting phenomena of incident energy dependence of $v_{1}$ and $v_{2}$ for thermal photons in central collisions also confirmed that it can be regarded as a good probe of evolution dynamics. Moreover, the multiplicities of hard photons and free nucleons and their correlation are also investigated. We find that direct photon emission is positively related to free nucleons emission, however, there exists an anti-correlation for thermal photons with free nucleons.
Comments:
9 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2010.05261 [pdf]
EPJA(2020)·4 citations
07
[Submitted on 12 Oct 2020]
Effect of the crust on neutron star empirical relations
Márcio Ferreira🇵🇹 · Constança Providência🇵🇹
We analyze how the crust equation of state affects several neutron star properties and how it impacts on possible constraints inferred from astrophysical observations. Using three distinct crusts, we generate three sets of model-independent equations of state describing stellar matter from a Taylor expansion around saturation density. The equations of state are thermodynamically consistent, causal, and compatible with astrophysical observations. The relations between the tidal deformability $Λ$ and compactness $C$ , Love number $k_{2}$ and radius of neutron star with mass $M$ are studied, and the effect of the crust equation of state on these relations analyzed. In most of the relations, the impact of the crust equation of state is not larger that 2\%. If, however, a fixed neutron star mass is considered, the relation between the tidal deformability and the radius depends on the crust. We have found that the relation $Λ_{M_{i}} = α R_{M_{i}}^{β}$ becomes almost exact and crust independent for massive neutron stars. It is shown that it is possible to determine the tidal deformability of an 1.4 $M_{⊙}$ star from the GW179817 effective tidal deformability $Λ ~$ with an accuracy of at least $\approx 10%$ . A high correlation between $Λ ~$ and the radius of the most massive star of the neutron star binary was confirmed, however, it was demonstrated that the crust has an effect of $\approx 14%$ on this relation. We have found that the relation $Λ_{1} / Λ_{2} = q^{a}$ depends on $M_{chirp}$ as $a \sim M_{chirp}$ .
Comments:
16 pages, 14 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2010.05588 [pdf]
PRD(2020)·11 citations
08
[Submitted on 12 Oct 2020]
Optimization and Supervised Machine Learning Methods for Fitting Numerical Physics Models without Derivatives
Raghu Bollapragada · Matt Menickelly · Witold Nazarewicz · Jared O'Neal · Paul-Gerhard Reinhard · Stefan M. Wild
We address the calibration of a computationally expensive nuclear physics model for which derivative information with respect to the fit parameters is not readily available. Of particular interest is the performance of optimization-based training algorithms when dozens, rather than millions or more, of training data are available and when the expense of the model places limitations on the number of concurrent model evaluations that can be performed. As a case study, we consider the Fayans energy density functional model, which has characteristics similar to many model fitting and calibration problems in nuclear physics. We analyze hyperparameter tuning considerations and variability associated with stochastic optimization algorithms and illustrate considerations for tuning in different computational settings.
Comments:
25-page article, 9-page supplement, 1-page notice
Subjects:
Nuclear Theory (nucl-th); math.OC (math.OC)
arXiv:
2010.05668 [pdf]
J.Phys.G(2021)·10 citations
09
[Submitted on 12 Oct 2020]
Modeling quasielastic interactions of monoenergetic kaon decay-at-rest neutrinos
Alexis Nikolakopoulos🇧🇪 · Vishvas Pandey🇺🇸 · Joshua Spitz🇺🇸 · Natalie Jachowicz🇧🇪
Monoenergetic muon neutrinos at 236 MeV are readily produced in intense medium-energy proton facilities ( $≳$ 2-3~GeV) when a positive kaon decays at rest (KDAR; $K^{+} \to μ^{+} ν_{μ}$ ). These neutrinos provide a unique opportunity to both study the neutrino interaction and probe the nucleus with a monoenergetic weak-interaction-only tool. We present cross section calculations for quasielastic scattering of these 236~MeV neutrinos off $^{12}$ C and $^{40}$ Ar, paying special attention to low-energy aspects of the scattering process. Our model takes the description of the nucleus in a mean-field (MF) approach as the starting point, where we solve Hartree-Fock (HF) equations using a Skyrme type nucleon-nucleon interaction. Thereby, we introduce long-range nuclear correlations by means of a continuum random phase approximation (CRPA) framework where we solve the CRPA equations using a Green's function method. The model successfully describes ( $e, e^{'}$ ) data on $^{12}$ C and $^{40}$ Ca in the kinematic region that overlaps with the KDAR $ν_{μ}$ phase space. In addition to these results, we present future prospects for precision KDAR cross section measurements and applications of our calculations in current and future experiments that will utilize these neutrinos.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2010.05794 [pdf]
PRC(2021)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE