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Nuclear Theory·nucl-th

Wednesday·November 20, 2019

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    Time-dependent approaches to open quantum systems

    M. Tokieda · K. Hagino

    Couplings of a system to other degrees of freedom (that is, environmental degrees of freedom) lead to energy dissipation when the number of environmental degrees of freedom is large enough. Here we discuss quantal treatments for such energy dissipation. To this end, we discuss two different time-dependent methods. One is to introduce an effective time-dependent Hamiltonian, which leads to a classical equation of motion as a relationship among expectation values of quantum operators. We apply this method to a heavy-ion fusion reaction and discuss the role of dissipation on the penetrability of the Coulomb barrier. The other method is to start with a Hamiltonian with environmental degrees of freedom and derive an equation which the system degree of freedom obeys. For this, we present a new efficient method to solve coupled-channels equations, which can be easily applied even when the dimension of the coupled-channels equations is huge.

    nucl-thphysics.chem-phquant-phFront.in Phys.(2020)·6 citations
  2. 02

    Recent shell-model calculations of gamma-decay strength functions

    Kamila Sieja🇫🇷 · Stéphane Goriely🇧🇪

    We present recent shell-model calculations of the gamma-decay in sd-pf and pf-shell nuclei. We focus on the M1 part of the dipole strength which was shown to exhibit interesting low-energy effects, in particular a low-energy enhancement which can have a considerable impact on the radiative neutron capture. We discuss the persistence of the shell effects in the nuclear quasi-continuum and the relation between the shape of the strength function at low energy and nuclear deformation.

    nucl-thActa Phys.Polon.Supp.(2020)·0 citations
  3. 03

    Simplified dynamical eikonal approximation

    Chloë Hebborn · Daniel Baye

    Background: Breakup reactions are often used to probe the nuclear structure of halo nuclei. The eikonal model diverges for Coulomb breakup since it relies on the adiabatic approximation. To correct this weakness, a Coulomb-corrected eikonal method (CCE) using the Coulomb first-order-perturbation approximation was developed. Purpose: Since the CCE mixes two reaction models and treats the Coulomb and nuclear interactions on different footings, we study here an alternative approach. We develop a simplification to the dynamical eikonal approximation (S-DEA) which has a similar numerical cost as the usual eikonal model, and study its efficiency for both nuclear- and Coulomb-dominated breakup reactions. Methods: We compare the energy and parallel-momentum cross sections obtained with the dynamical eikonal approximation, the usual eikonal approximation, the CCE and the S-DEA. Results: The S-DEA leads to precise energy distributions for both breakup reactions. The corresponding parallel-momentum distributions obtained with the S-DEA are improved compared to the ones computed with the eikonal model. It is more efficient for nuclear-dominated breakup than the CCE since it reproduces better the shape and magnitude of the distribution. However, for the Coulomb breakup, the distribution lacks asymmetry. Conclusions: The simplification of the DEA developed in this work improves significantly the eikonal descriptions of breakup energy distribution for both Coulomb- and nuclear-dominated reactions. The asymmetry of the parallel-momentum distribution is enhanced for nuclear-dominated breakup. This study confirms that the asymmetry is due to dynamical effects. A direct prospect of this work would be to extend this model to two-neutron halo-nucleus projectiles.

    nucl-thquant-phPRC(2020)·3 citations
  4. 04

    Microscopic optical potential from chiral effective field theory

    T.R. Whitehead · Y. Lim · J.W. Holt

    We formulate a microscopic optical potential from chiral two- and three-body forces. The real and imaginary central terms of the optical potential are obtained from the nucleon self-energy in infinite matter, while the real spin-orbit term is extracted from a nuclear energy density functional constructed from the density matrix expansion using the same chiral potential. The density-dependent optical potential is then folded with the nuclear density distributions for selected Calcium isotopes resulting in energy-dependent nucleon-nucleus optical potentials from which we study proton-nucleus elastic scattering cross sections calculated using the TALYS reaction code. We compare the results of the microscopic calculations to phenomenological models and experimental data.

    nucl-thSpringer Proc.Phys.(2020)·0 citations
  5. 05

    Bulk viscosity and contact correlations in attractive Fermi gases

    Tilman Enss

    The bulk viscosity determines dissipation during hydrodynamic expansion. It vanishes in scale invariant fluids, while a nonzero value quantifies the deviation from scale invariance. For the dilute Fermi gas the bulk viscosity is given exactly by the correlation function of the contact density of local pairs. As a consequence, scale invariance is broken purely by pair fluctuations. These fluctuations give rise also to logarithmic terms in the bulk viscosity of the high-temperature nondegenerate gas. For the quantum degenerate regime I report numerical Luttinger-Ward results for the contact correlator and the dynamical bulk viscosity throughout the BEC-BCS crossover. The ratio of bulk to shear viscosity is found to exceed the kinetic theory prediction in the quantum degenerate regime. Near the superfluid phase transition the bulk viscosity is enhanced by critical fluctuations and has observable effects on dissipative heating, expansion dynamics and sound attenuation.

    ↳ cond-mat.quant-gasnucl-thPRL(2019)·40 citations
  6. 06

    Equilibrium constants of Hydrogen and Helium isotopes at low nuclear densities

    R. Bougault🇫🇷 · E. Bonnet🇫🇷 · B. Borderie🇫🇷 · A. Chbihi🇫🇷 · J. D. Frankland🇫🇷 · E. Galichet🇫🇷 · D. Gruyer🇫🇷 · M. Henri🇫🇷 · M. La Commara🇮🇹 · N. Le Neindre🇫🇷 · I. Lombardo🇮🇹 · O. Lopez🇫🇷 and 5 other authors

    Equilibrium constants for Hydrogen and Helium isotopes as a function of density and temperature are measured in the framework of the study made by Qin et al. [Qin L et al 2012 Phys. Rev. Lett. 108 172701]. We review and comment on all stages of the analysis and conclude that our measurements are not inconsistent with Qin et al. results. Improvements are being made to the initial analysis and we raise the issue of the binding energies which has to be clarified.

    ↳ nucl-exnucl-thJ.Phys.G(2020)·28 citations

Affiliations

first authorsco-authorsvia INSPIRE