Nuclear Theory·nucl-th

Wednesday·June 21, 2023

18 papers—8 primary·10 cross-listed

01
Polarized Photons from the Early Stages of Relativistic Heavy-Ion Collisions
Sigtryggur Hauksson🇫🇷 · Charles Gale🇨🇦
The polarization of real photons emitted from early-time heavy-ion collisions is calculated, concentrating on the contribution from bremsstrahlung and quark-antiquark annihilation processes at leading order in the strong coupling. The effect of an initial momentum space anisotropy of the parton distribution is evaluated using a model for the non-equilibrium scattering kernel for momentum broadening. The effect on the photon polarization is reported for different degrees of anisotropy. The real photons emitted early during in-medium interactions will be dominantly polarized along the beam axis.
nucl-thhep-phPRC(2024)·13 citations
02
Quantum theory of isomeric excitation of $^{229}$ Th in strong laser fields
Wu Wang · Xu Wang
A general quantum mechanical theory is developed for the isomeric excitation of $^{229}$ Th in strong femtosecond laser pulses. The theory describes the tripartite interaction between the nucleus, the atomic electrons, and the laser field. The nucleus can be excited both by the laser field and by laser-driven electronic transitions. Numerical results show that strong femtosecond laser pulses are very efficient in exciting the $^{229}$ Th nucleus, yielding nuclear excitation probabilities on the order of $1 0^{- 11}$ per nucleus per pulse. Laser-driven electronic excitations are found to be more efficient than direct optical excitations.
nucl-thphysics.atom-phPRResearch(2023)·7 citations
03
Relativistic two-body currents for one-nucleon knockout in electron-nucleus scattering
T. Franco-Munoz · J. García-Marcos · R. González-Jiménez · J.M. Udías
We present a detailed study of the contribution from two-body currents to the one-nucleon knockout process induced by electromagnetic interaction. The framework is a relativistic mean-field model (RMF) in which bound and scattering nucleons are consistently described as solutions of Dirac equation with potentials. We show results obtained with the most general expression of the two-body operator, in which the intermediate nucleons are described by relativistic mean-field bound states; then, we propose two approximations consisting in describing the intermediate states as nucleons in a relativistic Fermi gas, preserving the complexity and consistency in the initial and final states. These approximations simplify the calculations considerably, allowing us to provide outcomes in a reasonable computational time. The results obtained under these approximations are validated by comparing with those from the full model. Additionally, the theoretical predictions are compared with experimental data of the longitudinal and transverse responses of carbon 12. The agreement with data is outstanding for the longitudinal response, where the contribution from the two-body operator is negligible. In the transverse sector, the two-body current increases the response from 30 to 15%, depending on the approximations and kinematics, in general, improving the agreement with data.
nucl-thPRC(2023)·19 citations
04
Constraining the Woods-Saxon potential in fusion reactions based on the neural network
Zepeng Gao · Siyu Liu · Peiwei Wen · Zehong Liao · Yu Yang · Jun Su · Yongjia Wang · Long Zhu
The accurate determination of the nuclear interaction potential is essential for predicting the fusion cross sections and understanding the reaction mechanism, which plays an important role in the synthesis of superheavy elements. In this work, the neural network, which combines with the calculations of the fusion cross sections via the Hill-Wheeler formula, is developed to optimize the parameters of the Woods-Saxon potential by comparing the experimental values. The correlations between the parameters of Woods-Saxon potential and the reaction partners, which can be quantitatively fitted to a sigmoid-like function with the mass numbers, have been displayed manifestly for the first time. This study could promote the accurate estimation of nucleus-nucleus interaction potential in low energy heavy-ion collisions.
nucl-thPRC(2024)·13 citations
05
Analysis of a Skyrme energy density functional with deep learning
N. Hizawa · K. Hagino · K. Yoshida
Over the past decade, machine learning has been successfully applied in various fields of science. In this study, we employ a deep learning method to analyze a Skyrme energy density functional (Skyrme-EDF), that is a Kohn-Sham type functional commonly used in nuclear physics. Our goal is to construct an orbital-free functional that reproduces the results of the Skyrme-EDF. To this end, we first compute energies and densities of a nucleus with the Skyrme Kohn-Sham + Bardeen-Cooper-Schrieffer method by introducing a set of external fields. Those are then used as training data for deep learning to construct a functional which depends only on the density distribution. Applying this scheme to the $^{24}$ Mg nucleus with two distinct random external fields, we successfully obtain a new functional which reproduces the binding energy of the original Skyrme-EDF with an accuracy of about 0.04 MeV. The rate at which the neural network outputs the energy for a given density is about $1 0^{5}$ -- $1 0^{6}$ times faster than the Kohn-Sham scheme, demonstrating a promising potential for applications to heavy and superheavy nuclei, including the dynamics of fission.
nucl-thcond-mat.dis-nnPRC(2023)·15 citations
06
Bulk and neutron-proton asymmetry coefficients of the semi-empirical mass formula tuned to ground state mass excess of AME2020 and/or FRDM(2012)
Dalip Singh Verma · Vivek · Kushmakshi
Davidson et al. has extended Seeger's mass formula to non-zero excitation energies by introducing temperature-dependent coefficients in the liquid drop energy part of the semi-empirical mass formula, without considering the shell effects. The semi-empirical mass formula of Davidson et al. is applicable for the compound nucleus temperatures less than or equal to 4 MeV. The mass excess calculated using this mass formula including shell effects/corrections does not reproduce the ground state mass excesses of the new atomic mass evaluation data AME2020 and/or FRDM(2012) with its coefficients at zero temperature. So, the coefficients of the semi-empirical mass formula are needed to be tuned to reproduce the ground state mass excess of the nuclei in the recent atomic mass evaluation data AME2020 and/or FRDM(2012). The bulk and neutron-proton asymmetry coefficients of the semi-empirical mass formula of Davidson et al. with shell effects have been tuned to reproduce the mass excess data for all the nuclei of AME2020 (Z=1-118 and A=1-295) and the nuclei of FRDM(2012) (Z=8-136 and A=16-339, except 3456 nuclei which are also available in the AME2020 data) at zero temperature, i.e., the coefficients are tuned for 9420 nuclei known at present. The tuned bulk and neutron-proton asymmetry coefficients reproduce the mass excess of the new atomic mass evaluation data AME2020 and/or FRDM(2012) within a difference of less than 1 MeV and can be used for the applications/investigations in the areas of physics where high energies are experienced or nuclei involved are in excited states, e.g., fusion-evaporation and fusion-fission processes in heavy-ion reactions.
nucl-thAtom.Data Nucl.Data Tabl.(2024)·4 citations
07
Floating block method for quantum Monte Carlo simulations
Avik Sarkar🇩🇪 · Dean Lee🇺🇸 · Ulf-G. Meißner🇩🇪
Quantum Monte Carlo simulations are powerful and versatile tools for the quantum many-body problem. In addition to the usual calculations of energies and eigenstate observables, quantum Monte Carlo simulations can in principle be used to build fast and accurate many-body emulators using eigenvector continuation or design time-dependent Hamiltonians for adiabatic quantum computing. These new applications require something that is missing from the published literature, an efficient quantum Monte Carlo scheme for computing the inner product of ground state eigenvectors corresponding to different Hamiltonians. In this work, we introduce an algorithm called the floating block method, which solves the problem by performing Euclidean time evolution with two different Hamiltonians and interleaving the corresponding time blocks. We use the floating block method and nuclear lattice simulations to build eigenvector continuation emulators for energies of $^{4}$ He, $^{8}$ Be, $^{12}$ C, and $^{16}$ O nuclei over a range of local and non-local interaction couplings. From the emulator data, we identify the quantum phase transition line from a Bose gas of alpha particles to a nuclear liquid.
nucl-thcond-mat.quant-gashep-latquant-phPRL(2023)·10 citations
08
Decay properties of undetected superheavy nuclei with Z>110
A. Jain · P. K. Sharma · S. K. Jain · Dashty T. Akrawy · G. Saxena
A comprehensive study of favoured and unfavoured $α$ -decay, cluster decay, weak-decay along with spontaneous fission in undetected superheavy nuclei within the range for proton number 111 $\leq$ Z $\leq$ 118 and neutron number 161 $\leq$ N $\leq$ 192 is performed. Half-lives for various mentioned decays are estimated with good accuracy on the basis of NUBASE2020 and are found in excellent match with the known half-lives. $α$ -decay mode is found most probable in this wide range and correspondingly potential $α$ -decay chains are reckoned. Peculiarly, the chances of cluster emission, as well as weak-decay, are also anticipated in this region of the periodic chart which open new pathways of detection of superheavy nuclei.
nucl-thPhys.Scripta(2023)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE