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Nuclear Theory·nucl-th

Friday·July 22, 2016

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    Nuclear shape transitions, level density, and underlying interactions

    S. Karampagia · Vladimir Zelevinsky

    The configuration interaction approach to nuclear structure uses the effective Hamiltonian in a finite orbital space. The various parts of this Hamiltonian and their interplay are responsible for specific features of physics including the shape of the mean field and level density. This interrelation is not sufficiently understood. We intend to study phase transitions between spherical and deformed shapes driven by different parts of the nuclear Hamiltonian and to establish the presence of the collective enhancement of the nuclear level density by varying the shell-model matrix elements. Varying the interaction matrix elements we define, for nuclei in the sd and pf shells, the sectors with spherical and deformed shapes. Using the moments method that does not require the full diagonalization we relate the shape transitions with the corresponding level density. Enhancement of the level density in the low-energy part of the spectrum is observed in clear correlation with a deformation phase transition induced mainly by the matrix elements of single-particle transfer. The single-particle transfer matrix elements in the shell model nuclear Hamiltonian are indeed the carriers of deformation, providing rotational observables and enhanced level densities.

    nucl-thPRC(2016)·17 citations
  2. 02

    Timescales in heavy ion collisions

    Mike Lisa🇺🇸

    The study of high energy collisions between heavy nuclei is a field unto itself, distinct from nuclear and particle physics. A defining aspect of heavy ion physics is the importance of a bulk, self-interacting system with a rich space-time substructure. I focus on the issue of timescales in heavy ion collisions, starting with proof from low-energy collisions that femtoscopy can, indeed, measure very long timescales. I then discuss the relativistic case, where detailed measurements over three orders of magnitude in energy reveal a timescale increase that might be due to a first-order phase transition. I discuss also consistency in evolution timescales as determined from traditional longitudinal sizes and a novel analysis using shape information.

    nucl-thhep-phActa Phys.Polon.B(2016)·6 citations
  3. 03

    Microscopic effective reaction theory for deuteron-induced reactions

    Yuen Sim Neoh · Kazuki Yoshida · Kosho Minomo · Kazuyuki Ogata

    The microscopic effective reaction theory is applied to deuteron-induced reactions. A reaction model-space characterized by a three-body model is adopted, where A is the target nucleus, and the nucleon-target potential is described by a microscopic folding model based on an effective nucleon-nucleon interaction in nuclear medium and a one-body nuclear density of A. The three-body scattering wave function in the model space is obtained with the continuum-discretized coupled-channels method (CDCC), and the eikonal reaction theory (ERT), an extension of CDCC, is applied to the calculation of neutron removal cross sections. Elastic scattering cross sections of deuteron on Ni and Pb target nuclei at several energies are compared with experimental data. The total reaction cross sections and the neutron removal cross sections at 56 MeV on 14 target nuclei are calculated and compared with experimental values.

    nucl-thPRC(2016)·18 citations
  4. 04

    Small systems and regulator dependence in relativistic hydrodynamics

    Michal Spalinski🇵🇱

    Consistent theories of hydrodynamics necessarily include nonhydrodynamic modes, which can be viewed as a regulator necessary to ensure causality. Under many circumstances the choice of regulator is not relevant, but this is not always the case. In particular, for sufficiently small systems (such as those arising in pA or pp collisions) such dependence may be inevitable. We address this issue in the context of the modern version of Müller-Israel-Stewart theory of relativistic hydrodynamics. In this case, by demanding that the nonhydrodynamic modes be subdominant, we find that regulator dependence becomes inevitable only for multiplicities of the order of a few. This conclusion supports earlier studies based on hydrodynamic simulations of small systems, at the same time providing a simple physical picture of how hydrodynamics can be reliable even in such seemingly extreme conditions.

    nucl-thPRD(2016)·34 citations
  5. 05

    On neutron stars in f(R) theories: small radii, large masses and large energy emitted in a merger

    Miguel Aparicio Resco🇪🇸 · Alvaro de la Cruz-Dombriz🇿🇦 · Felipe J. Llanes-Estrada🇪🇸 · Victor Zapatero Castrillo🇪🇸

    In the context of f(R) gravity theories, we show that the apparent mass of a neutron star as seen from an observer at infinity is numerically calculable but requires careful matching, first at the star's edge, between interior and exterior solutions, none of them being totally Schwarzschild-like but presenting instead small oscillations of the curvature scalar R; and second at large radii, where the Newtonian potential is used to identify the mass of the neutron star. We find that for the same equation of state, this mass definition is always larger than its general relativistic counterpart. We exemplify this with quadratic and Hu-Sawicki-like modifications of the standard General Relativity action. Therefore, the finding of two-solar mass neutron stars basically imposes no constraint on stable f(R) theories. However, star radii are in general smaller than in General Relativity, which can give an observational handle on such classes of models at the astrophysical level. Both larger masses and smaller matter radii are due to much of the apparent effective energy residing in the outer metric for scalar-tensor theories. Finally, because the f(R) neutron star masses can be much larger than General Relativity counterparts, the total energy available for radiating gravitational waves could be of order several solar masses, and thus a merger of these stars constitutes an interesting wave source.

    ↳ gr-qcastro-ph.COnucl-thPhys.Dark Univ.(2016)·109 citations
  6. 06

    Effects of Nuclear Potential on the Cumulants of Net-Proton and Net-Baryon Multiplicity Distributions in Au+Au Collisions at

    Shu He🇨🇳 · Xiaofeng Luo🇨🇳 · Yasushi Nara🇯🇵 · ShinIchi Esumi🇯🇵 · Nu Xu🇨🇳

    We analyze the rapidity and transverse momentum dependence for the cumulants of the net-proton and net-baryon distributions in Au+Au collisions at with a microscopic hadronic transport (JAM) model. To study the effects of mean field potential and softening of equation of state (EoS) on the fluctuations of net-proton (baryon) in heavy-ion collisions, the calculations are performed with two different modes. The softening of EoS is realized in the model by implementing the attractive orbit in the two-body scattering to introduce a reduction pressure of the system. By comparing the results from the two modes with the results from default cascade, we find the mean field potential and softening of EoS have strong impacts on the rapidity distributions () and the shape of the net-proton (baryon) multiplicity distributions. The net-proton (baryon) cumulants and their ratios calculated from all of the three modes are with similar trends and show significant suppression with respect to unity, which can be explained by the presence of baryon number conservations. It indicates that the effects of mean field potential and softening of EoS might be not the ingredients that are responsible to the observed strong enhancement in the most central Au+Au collisions at 7.7 GeV measured by the STAR experiment at RHIC.

    ↳ nucl-exnucl-thPLB(2016)·34 citations

Affiliations

first authorsco-authorsvia INSPIRE