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Nuclear Theory·nucl-th

Monday·June 12, 2017

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    Higher-order symmetry energy and neutron star core-crust transition with Gogny forces

    C. Gonzalez-Boquera · M. Centelles · X. Viñas · A. Rios

    We study the symmetry energy and the core-crust transition in neutron stars using the finite-range Gogny nuclear interaction and examine the deduced crustal thickness and crustal moment of inertia. We start by analyzing the second-, fourth- and sixth-order coefficients of the Taylor expansion of the energy per particle in powers of the isospin asymmetry for Gogny forces. These coefficients provide information about the departure of the symmetry energy from the widely used parabolic law. The neutron star core-crust transition is evaluated by looking at the onset of thermodynamical instability of the liquid core. The calculation is performed with the exact (i.e., without Taylor expansion) Gogny EoS for the core, and also with its Taylor expansion in order to assess the influence of isospin expansions on locating the inner edge of neutron star crusts. It is found that the properties of the core-crust transition derived from the exact EoS differ from the predictions of the Taylor expansion even when the expansion is carried through sixth order in the isospin asymmetry. Gogny forces, using the exact EoS, predict the ranges for the transition density and for the transition pressure. The transition densities show an anticorrelation with the slope parameter of the symmetry energy. The transition pressures are not found to correlate with . Neutron stars obtained with Gogny forces have maximum masses below and relatively small moments of inertia. The crustal mass and moment of inertia are evaluated and comparisons are made with the constraints from observed glitches in pulsars.

    nucl-thastro-ph.SRPRC(2017)·79 citations
  2. 02

    Partial correlation analysis method in ultra-relativistic heavy-ion collisions

    Adam Olszewski🇵🇱 · Wojciech Broniowski🇵🇱

    We argue that statistical data analysis of two-particle longitudinal correlations in ultra-relativistic heavy-ion collisions may be efficiently carried out with the technique of partial covariance. In this method, the spurious event-by-event fluctuations due to imprecise centrality determination are eliminated via projecting out the component of the covariance influenced by the centrality fluctuations. We bring up the relationship of the partial covariance to the conditional covariance. Importantly, in the superposition approach, where hadrons are produced independently from a collection of sources, the framework allows us to impose centrality constraints on the number of sources rather than hadrons, that way unfolding of the trivial fluctuations from statistical hadronization and focusing better on the initial-state physics. We show, using simulated data from hydrodynamics followed with statistical hadronization, that the technique is practical and very simple to use, giving insight into the correlations generated in the initial stage. We also discuss the issues related to separation of the short- and long-range components of the correlation functions, and show that in our example the short-range component from the resonance decays is largely reduced by considering pions of the same sign. We demonstrate the method explicitly on the cases where centrality is determined with a single central control bin, or with two peripheral control bins.

    nucl-thnucl-exPRC(2017)·17 citations
  3. 03

    A new temperature dependent hyperonic equation of state: application to rotating neutron star models and I-Q-relations

    Miguel Marques🇫🇷 · Micaela Oertel🇫🇷 · Matthias Hempel🇨🇭 · Jérôme Novak🇫🇷

    In this work we present a newly constructed equation of state (EoS) --applicable to stellar core collapse and neutron star mergers--, including the entire baryon octet. Our EoS is compatible with the main constraints from nuclear physics and, in particular, with a maximum mass for cold beta-equilibrated neutron stars of 2 solar masses in agreement with recent observations. As an application of our new EoS, we compute numerical stationary models for rapidly (rigidly) rotating hot neutron stars. We consider maximum masses of hot stars, such as proto-neutron stars or hypermassive neutron stars in the post-merger phase of binary neutron star coalescence. The universality of I-Q-relations at nonzero temperature for fast rotating models, comparing a purely nuclear EoS with its counterparts containing Lambda-hyperons or the entire baryon octet, respectively, is discussed, too. We find that the I-Q universality is broken when thermal effects become important, whatever the value of entropy gradients in our models. Thus, the use of I-Q relations for the analysis of proto-neutron stars or merger remnant data, including gravitational wave signals from the last stages of binary neutron star mergers, should be regarded with care.

    nucl-thastro-ph.HEPRC(2017)·114 citations
  4. 04

    Optical properties of an anisotropic hot QCD medium

    M. Yousuf Jamal · Sukanya Mitra · Vinod Chandra

    The present investigation involves explorations on the chromo-dielectric properties of the hot QCD medium produced in relativistic heavy-ion collisions in terms of refractive index. The isotropic/equilibrium modelling is done within an effective quasi-particle model of hot QCD medium. The possibilities of negative refraction in the medium are also explored in terms of the Depine-Lakhtakia index. The anisotropic aspects of the hot QCD medium are incorporated by introducing the anisotropy in a particular direction. That makes the medium quite similar to uniaxial crystals, and hence we observe phenomenon of birefringence ( two distinct refractive indices in the anisotropic case). Interestingly, both anisotropy and medium effects play significant roles in deciding the optical properties of the hot QCD/Quark-Gluon-Plasma (QGP) medium.

    nucl-th1 citation

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