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Nuclear Theory·nucl-th

Friday·April 6, 2018

7 papers—5 primary·2 cross-listed

All7Primary5Cross-lists2
  1. 01

    Statistical theory of deformation distributions in nuclear spectra

    M. T. Mustonen · C. N. Gilbreth · Y. Alhassid · G. F. Bertsch

    The dependence of the nuclear level density on intrinsic deformation is an important input to dynamical nuclear processes such as fission. Auxiliary-field Monte Carlo (AFMC) method is a powerful method for computing nuclear level densities. However, the statistical distribution of intrinsic shapes is not readily accessible due to the formulation of AFMC in a spherical configuration-interaction shell-model approach. Instead, theory of deformation up to now has largely relied on a mean-field approximation which breaks rotational symmetry. We show here how the distributions of the intrinsic quadrupole deformation parameters can be calculated within the AFMC method, and present results for a chain of even-mass samarium nuclei (Sm, Sm, Sm, Sm) which includes spherical, transitional, and strongly deformed isotopes. The method relies on a Landau-like expansion of the Helmholtz free energy in invariant polynomials of the quadrupole tensor. We find that an expansion to fourth order provides an excellent description of the AFMC results.

    nucl-thcond-mat.mes-hallcond-mat.stat-mechPRC(2018)·23 citations
  2. 02

    Computing the dipole polarizability of 48Ca with increased precision

    Mirko Miorelli · Sonia Bacca · Gaute Hagen · Thomas Papenbrock

    We compute the electric dipole polarizability of 48Ca with an increased precision by including more correlations than in previous studies. Employing the coupled-cluster method we go beyond singles and doubles excitations and include leading-order three-particle-three-hole (3p-3h) excitations for the ground state, excited states, and the similarity transformed operator. We study electromagnetic sum rules, such as the bremsstrahlung sum rule m_0 and the polarizability sum rule alpha_D using interactions from chiral effective field theory. To gauge the quality of our coupled-cluster approximations we perform several benchmarks with the effective interaction hyperspherical harmonics approach in 4He and with self consistent Green's function in 16O. We compute the dipole polarizability of 48Ca employing the chiral interaction N2LOsat [Ekstroem et al., Phys. Rev. C 91, 051301 (2015)] and the 1.8/2.0 (EM) [Hebeler et al., Phys. Rev. C 83, 031301 (2011)]. We find that the effect of 3p-3h excitations in the ground state is small for 1.8/2.0 (EM) but non-negligible for N2LOsat. The addition of these new correlations allows us to improve the precision of our 48Ca calculations and reconcile the recently reported discrepancy between coupled-cluster results based on these interactions and the experimentally determined alpha_D from proton inelastic scattering in 48Ca [Birkhan et al., Phys. Rev. Lett. 118, 252501 (2017)]. For the computation of electromagnetic and polarizability sum rules, the inclusion of leading-order 3p-3h excitations in the ground state is important, while less so for the excited states and the similarity-transformed dipole operator.

    nucl-thPRC(2018)·46 citations
  3. 03

    Effects of Tensor Force in the Relativistic Scheme: A Case Study of Neutron Drops

    Shihang Shen · Haozhao Liang · Jie Meng · Peter Ring · Shuangquan Zhang

    Tensor force is an important component in the nucleon-nucleon interaction, nevertheless, the role of the tensor force in the spin properties in finite nuclei is much less clear. In this report, we mainly focus on our recent progress on this topic about the relativistic Brueckner-Hartree-Fock theory and the corresponding tensor effects on the spin-orbit splittings in neutron drops. This will serve as an important guide for future microscopic derivations of the relativistic and non-relativistic nuclear energy density functionals.

    nucl-thnucl-exJPS Conf.Proc.(2018)·0 citations
  4. 04

    Constituent-quark model with pionic contributions: electromagnetic transition

    Ju-Hyun Jung🇦🇹 · Wolfgang Schweiger🇦🇹 · Elmar P. Biernat🇵🇹

    We report on ongoing work to determine the pion-cloud contribution to the electromagnetic transition form factors. The starting point is an spin-flavor symmetric constituent-quark model with instantaneous confinement that is augmented by dynamical pions which couple directly to the quarks. This system is treated in a relativistically invariant way within the framework of point-form quantum mechanics using a multichannel formulation. The first step is to determine the electromagnetic form factors of the bare particles that consist only of three quarks. These form factors are basic ingredients for calculating the pion-cloud contributions. Already without the pion cloud, electromagnetic nucleon and transition form factors compare reasonably well with the data. By inclusion of the pion-cloud contribution coming from the - intermediate state the reproduction of the data is further improved.

    nucl-thhep-phFew Body Syst.(2019)·2 citations
  5. 05

    One particle distribution function and shear viscosity in magnetic field: a relaxation time approach

    Payal Mohanty🇮🇳 · Ashutosh Dash🇮🇳 · Victor Roy🇮🇳

    We calculate the correction to the one particle distribution function in presence of magnetic field and non-zero shear viscosity within the relaxation time approximation. The correction is found to be electric charge dependent. Subsequently, we also calculate one longitudinal and four transverse shear viscous coefficients as a function of dimensionless Hall parameter in presence of the magnetic field. We find that a proper linear combination of the shear viscous coefficients calculated in this work scales with the result obtained from Grad's moment method in \cite{Denicol:2018rbw}. Calculation of invariant yield of in a simple Bjorken expansion with cylindrical symmetry shows no noticeable change in spectra due to the correction for realistic values of the magnetic field and relaxation time. However, when transverse expansion is taken into account using a blast wave type flow field we found noticeable change in spectra and elliptic flow coefficients due to the correction. The is also found to be very sensitive on the magnitude of magnetic field. Hence we think it is important to take into account the correction in more realistic numerical magnetohydrodynamics simulations.

    nucl-thEPJA(2019)·42 citations
  6. 06

    Revisiting the pseudoscalar meson and glueball mixing and key issues in the search for pseudscalar glueball state

    Wen Qin🇨🇳 · Qiang Zhao🇨🇳 · Xian-Hui Zhong🇨🇳

    We revisit the mixing mechanism for pesudscalar mesons and glueball which is introduced by the axial vector anomaly. We demonstrate that the physical mass of the pseudoscalar glueball does not favor to be lower than 1.8 GeV if all the parameters are reasonably constrained. This conclusion, on the one hand, can accommodate the pseudoscalar glueball mass calculated by Lattice QCD, and on the other hand, is consistent with the high-statistics analyses at BESIII that all the available measurements do not support the presence of two closely overlapping pseudoscalar states in any exclusive channel. Such a result is in agreement with the recent claim that the slightly shifted peak positions for two possible states and observed in different channels are actually originated from one single state with the triangle singularity interferences. By resolving this long-standing paradox, one should pay more attention to higher mass region for the purpose of searching for the pseudoscalar glueball candidate.

    ↳ hep-phhep-exnucl-exnucl-thPRD(2018)·25 citations
  7. 07

    Spectral function for overoccupied gluodynamics from real-time lattice simulations

    K. Boguslavski🇫🇮 · A. Kurkela🇨🇭 · T. Lappi🇫🇮 · J. Peuron🇫🇮

    We study the spectral properties of a highly occupied non-Abelian non-equilibrium plasma appearing ubiquitously in weak coupling descriptions of QCD matter. The spectral function of this far-from-equilibrium plasma is measured by employing linear response theory in classical-statistical real-time lattice Yang-Mills simulations. We establish the existence of transversely and longitudinally polarized quasiparticles and obtain their dispersion relations, effective mass, plasmon frequency, damping rate and further structures in the spectral and statistical functions. Our new method can be interpreted as a non-perturbative generalization of hard thermal loop (HTL) effective theory. We see indications that our results approach leading order HTL in the appropriate limit. The method can also be employed beyond the range of validity of HTL.

    ↳ hep-phhep-latnucl-thPRD(2018)·73 citations

Affiliations

first authorsco-authorsvia INSPIRE