Nuclear Theory·nucl-th
13 papers—7 primary·6 cross-listed
We perform quantum calculations of fluctuations of the electromagnetic fields in collisions at RHIC and LHC energies. We find that in the quantum picture the field fluctuations are much smaller than predictions of the classical Monte-Carlo simulation with the Woods-Saxon nuclear density.
P. Van Isacker🇫🇷 · J. Engel🇺🇸 · K. Nomura🇫🇷
Background: The interacting boson model (IBM) has been used extensively to calculate the matrix elements governing neutrinoless double-beta decay. Studies within other models indicate that a good description of neutron-proton pairing is essential for accurate calculations of those matrix elements. The usual interacting boson model is based only on like-particle pairs, however, and the extent to which it captures neutron-proton pairing is not clear. Purpose: To determine whether neutron-proton pairing should be explicitly included as neutron-proton bosons in IBM calculations of neutrinoless double-beta decay matrix elements. Method: An isospin-invariant version of the nucleon-pair shell model is applied to carry out shell-model calculations in a large space and in a collective subspace, and to define effective operators in the latter. A democratic mapping is then used to define corresponding boson operators for the IBM, with and without an isoscalar neutron-proton pair boson. Results: IBM calculations with and without the isoscalar boson are carried out for nuclei near the beginning of the shell, with a realistic shell-model Hamiltonian and neutrinoless double-beta-decay operator as the starting point. Energy spectra and double-beta matrix elements are compared to those obtained in the underlying shell model. Conclusions: The isoscalar boson does not improve energy spectra but does improve double-beta matrix elements. To be useful at the level of precision we need, the mapping procedure must be further developed to better determine the dependence of the boson Hamiltonian and decay operator on particle number and isospin. But the benefits provided by the isoscalar boson suggest that through an appropriate combination of mappings and fitting, it would make IBM matrix elements more accurate for the heavier nuclei used in experiments.
A separable form of the Gogny pairing force is implemented in tilted axis cranking covariant density functional theory for the description of rotational bands in open shell nuclei. The developed method is used to investigate the yrast sequence of 109Ag for an example. The experimental energy spectrum, angular momenta, and electromagnetic transition probabilities are well reproduced by taking into account pairing correlations with the separable pairing force. An abrupt transition of the rotational axis from the long-intermediate plane to the long-short one is obtained and discussed in detail.
Eduardo Antonio Coello Pérez · Javier Menéndez · Achim Schwenk
We study decays within an effective theory that treats nuclei as a spherical collective core with an even number of neutrons and protons that can couple to an additional neutron and/or proton. First we explore Gamow-Teller decays of parent odd-odd nuclei into low-lying ground-, one-, and two-phonon states of the daughter even-even system. The low-energy constants of the effective theory are adjusted to data on decays to ground states or Gamow-Teller strengths. The corresponding theoretical uncertainty is estimated based on the power counting of the effective theory. For a variety of medium-mass and heavy isotopes the theoretical matrix elements are in good agreement with experiment within the theoretical uncertainties. We then study the two-neutrino double- decay into ground and excited states. The results are remarkably consistent with experiment within theoretical uncertainties, without the necessity to adjust any low-energy constants.
Y. Yamamoto · H. Togashi · T. Tamagawa · T. Furumoto · N. Yasutake · Th.A. Rijken
The existence of neutron stars with requires the strong stiffness of the equation of state (EoS) of neutron-star matter. We introduce a multi-pomeron exchange potential (MPP) working universally among 3- and 4-baryons to stiffen the EoS. Its strength is restricted by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The EoSs are derived using the Brueckner-Hartree-Fock (BHF) and the cluster variational method (CVM) with the nuclear interactions ESC and AV18. The mass-radius relations are derived by solving the Tolmann-Oppenheimer-Volkoff (TOV) equation, where the maximum masses over are obtained on the basis of the terrestrial data. Neutron-star radii at a typical mass are predicted to be km. The uncertainty of calculated radii is mainly from the ratio of 3- and 4-pomeron coupling constants, which cannot be fixed by any terrestrial experiment. Though values of are not influenced by hyperon-mixing effects, finely-observed values for them indicate degrees of EoS softening by hyperon mixing in the region of . If is less than about 12.4 km, the softening of EoS by hyperon mixing has to be weak. Useful information can be expected by the space mission NICER offering precise measurements for neutron-star radii within .
Jaroslava Hrtánková🇨🇿 · Jiří Mareš🇨🇿
An optical potential constructed using the scattering amplitudes derived from the 2009 version of the Paris potential is applied in calculations of quasi-bound states in selected nuclei across the periodic table. A proper self-consistent procedure for treating energy dependence of the amplitudes in a nucleus appears crucial for evaluating binding energies and widths. Particular attention is paid to the role of -wave amplitudes. While the -wave potential nearly does not affect calculated binding energies, it reduces considerably the corresponding widths. The Paris -wave potential supplemented by a phenomenological -wave term yields in dynamical calculations binding energies MeV and widths MeV, which is very close to the values obtained within the RMF model consistent with -atom data.
We present a symmetry-based approach for shape coexistence in nuclei, founded on the concept of partial dynamical symmetry (PDS). The latter corresponds to a situation when only selected states (or bands of states) of the coexisting configurations preserve the symmetry while other states are mixed. We construct explicitly critical-point Hamiltonians with two or three PDSs of the type U(5), SU(3), and SO(6), appropriate to double or triple coexistence of spherical, prolate, oblate and -soft deformed shapes, respectively. In each case, we analyze the topology of the energy surface with multiple minima and corresponding normal modes. Characteristic features and symmetry attributes of the quantum spectra and wave functions are discussed. Analytic expressions for quadrupole moments and rates involving the remaining solvable states are derived and isomeric states are identified by means of selection rules.
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