Nuclear Theory·nucl-th

Thursday·March 12, 2015

10 papers—10 primary·0 cross-listed

01
Neutron stars in the BPS Skyrme model: mean-field limit vs. full field theory
C. Adam🇪🇸 · C. Naya🇪🇸 · J. Sanchez-Guillen🇪🇸 · R. Vazquez🇪🇸 · A. Wereszczynski🇵🇱
Using a solitonic model of nuclear matter, the BPS Skyrme model, we compare neutron stars obtained in the full field theory, where gravitational back reaction is completely taken into account, with calculations in a mean-field approximation using the Tolman-Oppenheimer-Volkoff approach. In the latter case, a mean-field-theory equation of state is derived from the original BPS field theory. We show that in the full field theory, where the energy density is non-constant even at equilibrium, there is no universal and coordinate independent equation of state of nuclear matter, in contrast to the mean-field approximation. We also study how neutron star properties are modified by going beyond mean field theory, and find that the differences between mean field theory and exact results can be considerable. Further, we compare both exact and mean-field results with some theoretical and phenomenological constraints on neutron star properties, demonstrating thus the relevance of our model even in its most simple version.
nucl-thastro-ph.SRhep-thPRC(2015)·53 citations
02
A study of the almost sequential mechanism of true ternary fission
R. B. Tashkhodjaev (1 and 2) · A. I. Muminov (2) · A. K. Nasirov (2 and 3 and 4) · W. von Oertzen (5 and 6) · Yongseok Oh (4 and 7) ((1) Institute of Nuclear Physics, Uzbek Academy of Science, Tashkent, Uzbekistan, (2) Inha University in Tashkent, Uzbekistan, (3) Joint Institute for Nuclear Research, Dubna, Russia, (4) Department of Physics, Kyungpook National University, Daegu, Republic Korea, (5) Helmholtz-Zentrum Berlin, Germany, (6) Fachbereich Physik, Freie Universität, Berlin, Germany, (7) Asia Pacific Center for Theoretical Physics, Pohang, Republic Korea)
We consider the collinear ternary fission which is a sequential ternary decay with a very short time between the ruptures of two necks connecting the middle cluster of the ternary nuclear system and outer fragments. In particular, we consider the case where the Coulomb field of the first massive fragment separated during the first step of the fission produces a lower pre-scission barrier in the second step of the residual part of the ternary system. In this case, we obtain a probability of about $1 0^{- 3}$ for the yield of massive clusters such as \nuclide[70]{Ni}, \nuclide[80-82]{Ge}, \nuclide[86]{Se}, and \nuclide[94]{Kr} in the ternary fission of \nuclide[252]{Cf}. These products appear together with the clusters having mass numbers of $A = 132$ -- $140$ . The results show that the yield of a heavy cluster such as \nuclide[68-70]{Ni} would be followed by a product of $A = 138$ -- $148$ with a large probability as observed in the experimental data obtained with the FOBOS spectrometer at the Joint Institute for Nuclear Research. The third product is not observed. The landscape of the potential energy surface shows that the configuration of the Ni + Ca + Sn decay channel is lower about 12 MeV than that of the Ca + Ni + Sn channel. This leads to the fact, that the yield of Ni and Sn is large. The analysis on the dependence of the velocity of the middle fragment on mass numbers of the outer products leads to the conclusion that, in the collinear tripartition channel of \nuclide[252]{Cf}, the middle cluster has a very small velocity, which does not allow it to be found in experiments.
nucl-thPRC(2015)·21 citations
03
Continuum excitations of $^{26}$ O in a three-body model: $0^{+}$ and $2^{+}$ states
L.V. Grigorenko · M.V. Zhukov
The structure and decay dynamics for $0^{+}$ and $2^{+}$ continuum excitations of $^{26}$ O are investigated in a three-body $^{24}$ O+ $n$ + $n$ model. The validity of a simple approximation for the cross section profile for long-lived $2 n$ emission is demonstrated. A sequence of three $0^{+}$ monopole ("breathing mode" type) excited states is predicted. These states could probably be interpreted as analogues of Efimov states pushed in the continuum due to insufficient binding. The calculated energies of the $2^{+}$ states are related to the excitation spectrum of $^{25}$ O. We discuss the correlation between the predicted $^{26}$ O spectrum and experimental observations.
nucl-thPRC(2015)·23 citations
04
High-spin structures of $^{77, 79, 81, 83}$ As isotopes
Vikas Kumar · P.C. Srivastava · Irving O. Morales
In the present work we report comprehensive set of shell model calculations for arsenic isotopes. We performed shell model calculations with two recent effective interactions JUN45 and jj44b. The overall results for the energy levels and magnetic moments are in rather good agreement with the available experimental data. We have also reported competition of proton- and neutron-pair breakings analysis to identify which nucleon pairs are broken to obtain the total angular momentum of the calculated states. Further theoretical development is needed by enlarging model space by including $π 0 f_{7/2}$ and $ν 1 d_{5/2}$ orbitals.
nucl-thMod.Phys.Lett.A(2015)·4 citations
05
Relativistic quantum transport coefficients for second-order viscous hydrodynamics
Wojciech Florkowski🇵🇱 · Amaresh Jaiswal🇩🇪 · Ewa Maksymiuk🇵🇱 · Radoslaw Ryblewski🇵🇱 · Michael Strickland🇺🇸
We express the transport coefficients appearing in the second-order evolution equations for bulk viscous pressure and shear stress tensor using Bose-Einstein, Boltzmann, and Fermi-Dirac statistics for the equilibrium distribution function and Grad's 14-moment approximation as well as the method of Chapman-Enskog expansion for the non-equilibrium part. Specializing to the case of transversally homogeneous and boost-invariant longitudinal expansion of the viscous medium, we compare the results obtained using the above methods with those obtained from the exact solution of the massive 0+1d relativistic Boltzmann equation in the relaxation-time approximation. We show that compared to the 14-moment approximation, the hydrodynamic transport coefficients obtained by employing the Chapman-Enskog method leads to better agreement with the exact solution of the relativistic Boltzmann equation.
nucl-thhep-phPRC(2015)·72 citations
06
Study of vorticity in an exact rotating hydro model
L.P. Csernai🇳🇴 · J.H. Inderhaug🇳🇴
We study a semianalytic exact solution of the fluid dynamical model of heavy ion reactions, and evaluate some observable signs of the rotation.
nucl-thIJMPE(2015)·9 citations
07
Linear Boltzmann Transport for Jet Propagation in the Quark-Gluon Plasma: Elastic Processes and Medium Recoil
Yayun He (CCNU)🇨🇳 · Tan Luo (CCNU)🇨🇳 · Xin-Nian Wang (CCNU and LBNL)🇨🇳 · Yan Zhu (USC)🇪🇸
A Linear Boltzmann Transport model within perturbative QCD is developed for the study of parton propagation inside the quark-gluon plasma. Both leading partons and thermal recoil partons are tracked so that one can also study jet-induced medium excitations. In this study, we implement the complete set of elastic parton scattering processes and investigate elastic parton energy loss, transverse momentum broadening and their nontrivial energy and length dependence. We further investigate medium modifications of the jet shape and fragmentation functions of reconstructed jets. Contributions from thermal recoil partons are found to have significant influences on jet shape, fragmentation functions and angular distribution of reconstructed jets.
nucl-thhep-phPRC(2015)·315 citations
08
Baryonium, a common ground for atomic and high energy physics
S. Wycech🇵🇱 · J.P. Dedonder🇫🇷 · B. Loiseau🇫🇷
Indications of the existence of quasi-bound states in the N-Nbar system are presented. Measurements by BES discovered a broad enhancement close to the p-pbar threshold in the S wave, isospin 0 state formed in radiative decays of J/psi. Another enhancement located about 50 MeV below the threshold was found in mesonic decays of J/psi. In terms of the Paris potential model it was shown that these are likely to represent the same state. Antiprotonic atomic data provide some support for this interpretation and indicate the existence of another fairly narrow quasi-bound state in a P wave.
nucl-thhep-phHyperfine Interact.(2015)·4 citations
09
The beam energy dependence of collective flow in heavy ion collisions
Hannah Petersen🇩🇪 · Jan Steinheimer🇩🇪 · Jussi Auvinen🇺🇸 · Marcus Bleicher🇩🇪
The major goals of heavy ion research are to explore the phase diagram of quantum chromodynamics (QCD) and to investigate the properties of the quark gluon plasma (QGP), a new state of matter created at high temperatures and/or densities. Collective anisotropic flow is one of the most promising observables to gain insights about the properties of the system created in relativistic heavy ion reactions. The current status of the beam energy dependence of the first three Fourier coefficients of the azimuthal distribution of the produced particles $v_{1}$ to $v_{3}$ within hybrid transport plus hydrodynamics approaches are summarized.
nucl-thhep-phnucl-exPoS(2015)·2 citations
10
Microscopic analysis of fusion hindrance in heavy systems
Kouhei Washiyama
Background: Heavy-ion fusion reactions involving heavy nuclei at energies around the Coulomb barrier exhibit fusion hindrance, where the probability of compound nucleus formation is strongly hindered compared with that in light- and medium-mass systems. The origin of this fusion hindrance has not been well understood from a microscopic point of view. Purpose: Analyze the fusion dynamics in heavy systems by a microscopic reaction model and understand the origin of the fusion hindrance. Method: We employ the time-dependent Hartree-Fock (TDHF) theory. We extract nucleus--nucleus potential and energy dissipation by the method combining TDHF dynamics of the entrance channel of fusion reactions with one-dimensional Newton equation including a dissipation term. Then, we analyze the origin of the fusion hindrance using the properties of the extracted potential and energy dissipation. Results: Extracted potentials show monotonic increase as the relative distance of two nuclei decreases, which induces the disappearance of an ordinary barrier structure of the potential. This is different from those in light- and medium-mass systems and from density-constraint TDHF calculations. Extracted friction coefficients show sizable energy dependence and universal value of their magnitude, which are rather similar to those in light- and medium-mass systems. Using these properties, we analyze the origin of the fusion hindrance and find that contribution of the increase in potential to the extra-push energy is larger than that of the accumulated dissipation energy in most systems studied in this article. Conclusions: By the analysis of the origin of the fusion hindrance, we conclude that, as the system becomes heavier, the dynamical increase in potential at small relative distances plays a more important role than the dissipation during the fusion reaction for understanding the origin of the fusion hindrance.
nucl-thnucl-exPRC(2015)·31 citations

Affiliations

first authorsco-authorsvia INSPIRE