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Nuclear Theory·nucl-th

Thursday·October 19, 2023

9 papers—5 primary·4 cross-listed

All9Primary5Cross-lists4
  1. 01

    Determination of the Equation of State from Nuclear Experiments and Neutron Star Observations

    Chun Yuen Tsang🇺🇸 · ManYee Betty Tsang🇺🇸 · William G. Lynch🇺🇸 · Rohit Kumar🇺🇸 · Charles J. Horowitz🇺🇸

    With recent advances in neutron star observations, major progress has been made in determining the pressure of neutron star matter at high density. This pressure is constrained by the neutron star deformability, determined from gravitational waves emitted in a neutron-star merger, and measurements of radii of two neutron stars, using a new X-ray observatory on the International Space Station. Previous studies have relied on nuclear theory calculations to provide the equation of state at low density. Here we use a combination of 15 constraints composed of three astronomical observations and twelve nuclear experimental constraints that extend over a wide range of densities. Bayesian Inference is then used to obtain a comprehensive nuclear equation of state. This data-centric result provides benchmarks for theoretical calculations and modeling of nuclear matter and neutron stars. Furthermore, it provides insights on the composition of neutron stars and their cooling via neutrino radiation.

    nucl-thastro-ph.HEnucl-exNature Astron.(2024)·109 citations
  2. 02

    Non-empirical shape dynamics of heavy nuclei with multi-task deep learning

    N. Hizawa · K. Hagino

    A microscopic description of nuclear fission represents one of the most challenging problems in nuclear theory. While phenomenological coordinates, such as multipole moments, have often been employed to describe fission, it is not obvious whether these parameters fully reflect the shape dynamics of interest. We here propose a novel method to extract collective coordinates, which are free from phenomenology, based on multi-task deep learning in conjunction with a density functional theory (DFT). To this end, we first introduce randomly generated external fields to a Skyrme-EDF and construct a set of nuclear number densities and binding energies for deformed states of U around the ground state. By training a neural network on such dataset with a combination of an autoencoder and supervised learning, we successfully identify a two-dimensional latent variables that accurately reproduce both the energies and the densities of the original Skyrme-EDF calculations, within a mean absolute error of 113 keV for the energies. In contrast, when multipole moments are used as latent variables for training in constructing the decoders, we find that the training data for the binding energies are reproduced only within 2 MeV. This implies that conventional multipole moments do not provide fully adequate variables for a shape dynamics of heavy nuclei.

    nucl-thphysics.data-anPRC(2024)·2 citations
  3. 03

    The origin of correlation between mass and angle in quasi-fission

    S. Amano · Y. Aritomo · S. Ishizaki · M. Okubayashi · S. Okugawa

    Mass-angle distribution (MAD) measurement of heavy and superheavy element fragmentation reactions is one of the powerful tools for investigating the mechanism of fission and fusion process. MAD shows a strong correlation between mass and angle when the quasi-fission event is dominant. It has characteristic that appears diagonal correlation as long as the quasi-fission event is dominant. This diagonal correlation could not be reproduced in previous our model before the introduction of the parameters. In this study, we systematically evaluate the unknown model parameters contained in our model and clarify those model parameters to reproduce the diagonal correlation that appears in MAD. Using a dynamical model based on the fluctuation dissipation theorem that employs Langevin equations, we calculate MADs of two reaction systems Ti+W and S+Th which are dominated by quasi-fission. We were able to clarify the effects of unknown model parameters on the MAD. In addition, we identified the values of model parameters that can reproduce the correlation between mass and angle. As a result, it was found that the balance of tangential friction and moment of inertia values is important for the correlation between mass and angle.

    nucl-thJAEA-Conf 2021-001, p. 102
  4. 04

    Causal hydrodynamic fluctuations in a one-dimensional expanding system

    Shin-ei Fujii🇯🇵 · Tetsufumi Hirano🇯🇵

    We derive equations of motion of hydrodynamic fluctuations performing perturbative expansion of the energy-momentum conservation equations around the boost invariant solution in one-dimensional expanding system. In the course of derivation, we do not assume any specific forms of constitutive equations for shear stress tensor and bulk pressure . Therefore, the framework enables us to employ any constitutive equations beyond the Navier-Stokes theory which satisfy the causality. Employing Israel-Stewart equations as examples of the constitutive equations, we demonstrate the dynamics of causal hydrodynamic fluctuations in (1+1)-dimensional Milne coordinates. We observe that structure of energy density fluctuations is almost frozen in the early stage of the expansion. Two-point correlations of energy density fluctuations turn out to be closely related with the properties of the medium such as sound velocity, viscosity, and relaxation time. Furthermore, we show that two-particle correlation functions of final hadrons after freezeout inherit correlations of thermodynamic variables and flow rapidity. This opens a new door for an analysis of transport properties of the medium produced in relativistic heavy ion collisions.

    nucl-thhep-phnucl-exPRC(2024)·3 citations
  5. 05

    Modeling alpha-nucleus elastic scattering using a velocity-dependent optical model

    A. Saleh · M. I. Jaghoub

    We performed a least-square fit analysis to reproduce the elastic angular distributions for scattering on various nuclei form C to Pb for incident energies in the range 18 - 70 MeV using a velocity-dependent optical model. The model reproduced the experimental data well including the enhanced angular distributions in the large-angle scattering region, which is commonly known as the anomalous large angle scattering (ALAS). Our best-fit potential parameters are linear functions of incident energy. Although the ALAS effect is not present in the case of scattering on the intermediate Ni and heavy Pb nuclei, we considered these nuclei to demonstrate the effectiveness of the VDOM in describing the angular distributions for scattering on various light, intermediate and heavy nuclei. For scattering on Ca, we compared our results to two previous works that adopted the conventional optical model. One model reproduced the data better at low energies, while the other performed better at high energies. In contrast, the velocity-dependent model of this work described the data across the considered angular range.

    nucl-thPRC(2024)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE