Nuclear Theory·nucl-th

Thursday·May 26, 2016

9 papers—4 primary·5 cross-listed

01
Freezeout conditions in proton-proton collisions at the top RHIC and LHC energies
Sabita Das🇨🇳 · Debadeepti Mishra🇮🇳 · Sandeep Chatterjee🇮🇳 · Bedangadas Mohanty🇮🇳
The freezeout conditions in proton-proton collisions at $s_{NN} = 200$ , $900$ and $7000$ GeV have been extracted by fits to the mean hadron yields at mid-rapidity within the framework of the statistical model of an ideal gas of hadrons and resonances in the grand canonical ensemble. The variation of the extracted freezeout thermal parameters and the goodness of the fits with $s_{NN}$ are discussed. We find the extracted temperature and baryon chemical potential of the freezeout surface to be similar in p+p and heavy ion collisions. On the other hand, the thermal behaviour of the strange hadrons is qualitatively different in p+p as compared to A+A. We find an additional parameter accounting for non-equilibrium strangeness production is essential for describing the p+p data. This is in contrast to A+A where the non-equilibrium framework could be successfully replaced by a sequential and complete equilibrium model with an early freezeout of the strange hadrons.
nucl-thnucl-exPRC(2017)·26 citations
02
Global analysis of isospin dependent microscopic nucleon-nucleus optical potential in Dirac Bruckner Hartree-Fock approach
Ruirui Xu · Zhongyu Ma · Yue Zhang · Yuan Tian (China Institute of Atomic Energy, Beijing 102413) · E. N. E. van Dalen · H. Müther (Institut für Theoretische Physik, Universität Tübingen, Germany)
The Microscopic Otical Model Potential is evaluated within a relativistic scheme which provides a natural and consistent relation between the spin-orbit part and the central part of the potential. The Dirac-Brueckner-Hartree-Fock (DBHF) approach provides such a microscopic relativistic scheme, which is based on a realistic nucleon-nucleon interaction and reproduce the saturation properties of symmetric nuclear matter without any adjustable parameter. Its solution using the projection technique within the subtracted T-matrix (STM) representation provides a reliable extension to asymmetric nuclear matter, which is important to describe the features of the isospin asymmetric nuclei. Therefore, the present work aims to perform a global analysis of the isospin-dependent nucleon-nucleus MOP based on the DBHF calculation in symmetric and asymmetric nuclear matter. The DBHF is used to evaluate the relativistic structure of the nucleon self-energies in nuclear matter at various densities and asymmetries. The Schrödinger equivalent potentials of finite nuclei are derived from these Dirac components by a local density approximation (LDA). The nucleon-nucleus scattering calculations are carried out for a broad spectrum $n$ and $p$ scattering experiments below 200 MeV with targets ranging from $^{12}$ C to $^{208}$ Pb.
nucl-thPRC(2016)·22 citations
03
Single electrons from heavy-flavor mesons in relativistic heavy-ion collisions
Taesoo Song🇩🇪 · Hamza Berrehrah🇩🇪 · Juan M. Torres-Rincon🇩🇪 · Laura Tolos🇩🇪 · Daniel Cabrera🇪🇸 · Wolfgang Cassing🇩🇪 · Elena Bratkovskaya🇩🇪
We study the single electron spectra from $D -$ and $B -$ meson semileptonic decays in Au+Au collisions at $s_{NN} =$ 200, 62.4, and 19.2 GeV by employing the parton-hadron-string dynamics (PHSD) transport approach that has been shown to reasonably describe the charm dynamics at RHIC and LHC energies on a microscopic level. In this approach the initial heavy quarks are produced by using the PYTHIA which is tuned to reproduce the FONLL calculations. The produced heavy quarks interact with off-shell massive partons in QGP with scattering cross sections which are calculated in the dynamical quasi-particle model (DQPM). At energy densities close to the critical energy density the heavy quarks are hadronized into heavy mesons through either coalescence or fragmentation. After hadronization the heavy mesons interact with the light hadrons by employing the scattering cross sections from an effective Lagrangian. The final heavy mesons then produce single electrons through semileptonic decay. We find that the PHSD approach well describes the nuclear modification factor $R_{AA}$ and elliptic flow $v_{2}$ of single electrons in d+Au and Au+Au collisions at $s_{NN} =$ 200 GeV and the elliptic flow in Au+Au reactions at $s_{NN} =$ 62.4 GeV from the PHENIX collaboration, however, the large $R_{AA}$ at $s_{NN} =$ 62.4 GeV is not described at all. Furthermore, we make predictions for the $R_{AA}$ of $D -$ mesons and of single electrons at the lower energy of $s_{NN} =$ 19.2 GeV. Additionally, the medium modification of the azimuthal angle $ϕ$ between a heavy quark and a heavy antiquark is studied. We find that the transverse flow enhances the azimuthal angular distributions close to $ϕ =$ 0 because the heavy flavors strongly interact with nuclear medium in relativistic heavy-ion collisions and almost flow with the bulk matter.
nucl-thnucl-exPRC(2017)·38 citations
04
Emergent Kink Statistics at Finite Temperature
Miguel Angel Lopez-Ruiz🇺🇸 · Tochtli Yepez-Martinez🇺🇸 · Adam P. Szczepaniak🇺🇸 · Jinfeng Liao🇺🇸
In this paper we use 1D quantum mechanical systems with Higgs-like interaction potential to study the emergence of topological objects at finite temperature. Two different model systems are studied, the standard double-well potential model and a newly introduced discrete kink model. Using Monte-Carlo simulations as well as analytic methods, we demonstrate how kinks become abundant at low temperatures. These results may shed useful insights on how topological phenomena may occur in QCD.
nucl-thhep-phNPA(2017)·2 citations
05
The entanglement spectrum and Rényi entropies of non-relativistic conformal fermions
William J. Porter🇺🇸 · Joaquín E. Drut🇺🇸
We characterize non-perturbatively the Rényi entropies of degree n=2,3,4, and 5 of three-dimensional, strongly coupled many-fermion systems in the scale-invariant regime of short interaction range and large scattering length, i.e. in the unitary limit. We carry out our calculations using lattice methods devised recently by us. Our results show the effect of strong pairing correlations on the entanglement entropy, which modify the sub-leading behavior for large subsystem sizes (as characterized by the dimensionless parameter x=kF L_A, where kF is the Fermi momentum and L_A the linear subsystem size), but leave the leading order unchanged relative to the non-interacting case. Moreover, we find that the onset of the sub-leading asymptotic regime is at surprisingly small x=2-4. We provide further insight into the entanglement properties of this system by analyzing the spectrum of the entanglement Hamiltonian of the two-body problem from weak to strong coupling. The low-lying entanglement spectrum displays clear features as the strength of the coupling is varied, such as eigenvalue crossing, a sharp change in the Schmidt gap, and scale invariance at unitarity. Beyond the low-lying component, the spectrum appears as a quasi-continuum distribution, for which we present a statistical characterization; we find, in particular, that the mean shifts to infinity as the coupling is turned off, which indicates that that part of the spectrum represents non-perturbative contributions to the entanglement Hamiltonian. In contrast, the low-lying entanglement spectrum evolves to finite values in the noninteracting limit. The scale invariance of the unitary regime guarantees that our results are universal features intrinsic to 3D quantum mechanics and represent a well-defined prediction for ultracold atom experiments, which were recently shown to have direct access to the entanglement entropy.
↳ cond-mat.quant-gashep-lathep-thnucl-th+1PRB(2016)·11 citations
06
Electrical conductivity of a warm neutron star crust in magnetic fields
Arus Harutyunyan · Armen Sedrakian
We study the electrical conductivity of finite-temperature crust of a warm compact star which may be formed in the aftermath of a supernova explosion or a binary neutron star merger as well as when a cold neutron star is heated by accretion of material from a companion. We focus on the temperature-density regime where plasma is in the liquid state and, therefore, the conductivity is dominated by the electron scattering off correlated nuclei. The dynamical screening of this interaction is implemented in terms of the polarization tensor computed in the hard-thermal-loop effective field theory of QED plasma. The correlations of the background ionic component are accounted for via a structure factor derived from Monte Carlo simulations of one-component plasma. With this input we solve the Boltzmann kinetic equation in relaxation time approximation taking into account the anisotropy of transport due to the magnetic field. The electrical conductivity tensor is studied numerically as a function of temperature and density for carbon and iron nuclei as well as density-dependent composition of zero-temperature dense matter in weak equilibrium with electrons. We also provide accurate fit formulas to our numerical results as well as supplemental tables which can be used in dissipative magneto-hydrodynamics simulations of warm compact stars.
↳ astro-ph.HEastro-ph.SRnucl-thPRC(2016)·74 citations
07
The LPM effect in sequential bremsstrahlung 2: factorization
Peter Arnold🇺🇸 · Han-Chih Chang🇺🇸 · Shahin Iqbal🇺🇸
The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. In this paper, we continue analysis of the case when the coherence lengths of two consecutive splitting processes overlap (which is important for understanding corrections to standard treatments of the LPM effect in QCD), avoiding soft-gluon approximations. In particular, this paper analyzes the subtle problem of how to precisely separate overlapping double splitting (e.g.\ overlapping double bremsstrahlung) from the case of consecutive, independent bremsstrahlung (which is the case that would be implemented in a Monte Carlo simulation based solely on single splitting rates). As an example of the method, we consider the rate of real double gluon bremsstrahlung from an initial gluon with various simplifying assumptions (thick media; $q^$ approximation; large $N_{c}$ ; and neglect for the moment of processes involving 4-gluon vertices) and explicitly compute the correction $Δ d Γ/ d x d y$ due to overlapping formation times.
↳ hep-phnucl-thJHEP(2016)·47 citations
08
Radii and binding energies in oxygen isotopes: a puzzle for nuclear forces
V. Lapoux🇫🇷 · V. Somà🇫🇷 · C. Barbieri🇬🇧 · H. Hergert🇺🇸 · J.D. Holt🇨🇦 · S.R. Stroberg🇨🇦
We present a systematic study of both nuclear radii and binding energies in (even) oxygen isotopes from the valley of stability to the neutron drip line. Both charge and matter radii are compared to state-of-the-art {\it ab initio} calculations along with binding energy systematics. Experimental matter radii are obtained through a complete evaluation of the available elastic proton scattering data of oxygen isotopes. We show that, in spite of a good reproduction of binding energies, {\it ab initio} calculations with conventional nuclear interactions derived within chiral effective field theory fail to provide a realistic description of charge and matter radii. A novel version of two- and three-nucleon forces leads to considerable improvement of the simultaneous description of the three observables for stable isotopes, but shows deficiencies for the most neutron-rich systems. Thus, crucial challenges related to the development of nuclear interactions remain.
↳ nucl-exnucl-thPRL(2016)·136 citations
09
Exotic Discoveries in Familiar Places: Theory of the Onia and Exotics
Richard F. Lebed🇺🇸
This brief overview presents an introduction to the heavy-quark exotic hadron candidates, $X$ , $Y$ , $Z$ , $P_{c}$ , believed to be tetraquark and pentaquark states. After an abridged account of their discovery, we outline the various theoretical pictures employed to describe their structure, with special focus on the new dynamical diquark picture.
↳ hep-phnucl-thPoS(2016)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE