Nuclear Theory·nucl-th

Tuesday·May 30, 2017

8 papers—3 primary·5 cross-listed

01
Gluo-dissociation of Heavy Quarkonium in the Quark-Gluon Plasma Revisited
Shile Chen🇨🇳 · Min He🇨🇳
Using an effective Hamiltonian derived from the QCD multipole expansion, we calculate the cross sections of gluo-dissociation of heavy quarkonia in the quark-gluon plasma, by including both the chromo-electric dipole ( $E_{1}$ ) as well as the chromo-magnetic dipole ( $M_{1}$ ) transition mechanisms. While the former allows to reproduce the results from operator-product-expansion calculations in the Coulomb approximation, the latter as a novel contribution is shown to be significant at low energies close to the threshold. Using thus obtained cross sections, we further carry out a full calculation of the gluo-dissociation rates for various charmonia and bottomonia within a non-relativitic in-medium potential model. The $M_{1}$ contribution turns out to be most prominent for the $J / ψ$ and accounts for $\sim 10% - 25%$ of the total ( $E 1 + M 1$ ) dissociation rate at temperatures close to the transition temperature.
nucl-thhep-phPRC(2017)·19 citations
02
Anisotropic hydrodynamic modeling of 2.76 TeV Pb-Pb collisions
Mubarak Alqahtani🇺🇸 · Mohammad Nopoush🇺🇸 · Radoslaw Ryblewski🇵🇱 · Michael Strickland🇺🇸
We compare phenomenological results from 3+1d quasiparticle anisotropic hydrodynamics (aHydroQP) with experimental data collected in LHC 2.76 TeV Pb-Pb collisions. In particular, we present comparisons of particle spectra, average transverse momentum, elliptic flow, and HBT radii. The aHydroQP model relies on the introduction of a single temperature-dependent quasiparticle mass which is fit to lattice QCD data. By taking moments of the resulting Boltzmann equation, we obtain the dynamical equations used in the hydrodynamic stage which include the effects of both shear and bulk viscosities. At freeze-out, we use anisotropic Cooper-Frye freeze-out performed on a fixed-energy-density hypersurface to convert to hadrons. To model the production and decays of the hadrons we use THERMINATOR 2 which is customized to sample from ellipsoidal momentum-space distribution functions. Using smooth Glauber initial conditions, we find very good agreement with many heavy-ion collision observables.
nucl-thhep-phPRC(2017)·82 citations
03
Pentaquark states with hidden charm
Roelof Bijker🇲🇽
I develop an extension of the usual three-flavor quark model to four flavors (u, d, s and c), and discuss the classification of pentaquark states with hidden charm. This work is motivated by the recent observation of such states by the LHCb Collatoration at CERN.
nucl-thhep-exhep-phnucl-exJ.Phys.Conf.Ser.(2017)·1 citation
04
Bulk viscosity of two-flavor quark matter from the Kubo formalism
Arus Harutyunyan (ITP, Frankfurt)🇩🇪 · Armen Sedrakian (FIAS)🇩🇪
We study the bulk viscosity of quark matter in the strong coupling regime within the two-flavor Nambu--Jona-Lasinio model. The dispersive effects that lead to non-zero bulk viscosity arise from quark-meson fluctuations above the Mott transition temperature, where meson decay into two quarks is kinematically allowed. We adopt the Kubo-Zubarev formalism and compute the equilibrium imaginary-time correlation function for pressure in the $O (1/ N_{c})$ power counting scheme. The bulk viscosity of matter is expressed in terms of the Lorentz components of the quark spectral function and includes multi-loop contributions which arise via re-summation of infinite geometrical series of loop diagrams. We show that the multi-loop contributions dominate the single-loop contribution close to the Mott line, whereas at high temperatures the one-loop contribution is dominant. The multi-loop bulk viscosity dominates the shear viscosity close to the Mott temperature by factors 5 to 20, but with increasing temperature the shear viscosity becomes the dominant dissipation mechanism of stresses as the one-loop contribution becomes the main source of bulk viscosity.
↳ hep-phastro-ph.HEastro-ph.SRnucl-thPRD(2017)·13 citations
05
On the stability of strange dwarf hybrid stars
Mark G. Alford · Steven P. Harris · Pratik S. Sachdeva
We investigate the stability of stars with a density discontinuity between a high-density core and a very low density mantle. Previous work on "strange dwarfs" suggested that such a discontinuity could stabilize stars that would have been classified as unstable by the conventional criteria based on extrema in the mass-radius relation. We investigate the stability of such stars by numerically solving the Sturm-Liouville equations for the lowest-energy modes of the star. We find that the conventional criteria are correct, and strange dwarfs are not stable.
↳ astro-ph.HEnucl-thApJ(2017)·37 citations
06
Nuclear dependence of $R = \frac{σ _{L}}{σ _{T}}$ and Callan-Gross relation in nuclei
F. Zaidi🇮🇳 · H. Haider🇮🇳 · M. Sajjad Athar🇮🇳 · S. K. Singh🇮🇳 · I. Ruiz Simo🇪🇸
The electromagnetic nuclear structure functions $F_{1 A} (x, Q^{2})$ , $F_{2 A} (x, Q^{2})$ and $F_{L A} (x, Q^{2})$ have been calculated using a microscopic model of nucleus to study the nuclear medium effects on the ratio $R_{A} (x, Q^{2}) = \frac{σ _{L A} ( x , Q ^{2} )}{σ _{T A} ( x , Q ^{2} )} = \frac{F _{L A} ( x , Q ^{2} )}{2 x F _{1 A} ( x , Q ^{2} )}$ and the Callan-Gross relation(CGR) in nuclei. The nuclear medium effects due to the Fermi motion, binding energy, nucleon correlations, mesonic contribution and shadowing have been taken into account. The theoretical results for the nuclear dependence of $R_{A} (x, Q^{2})$ and its impact on CGR have been presented and compared with the available experimental data on the various nuclear targets. The predictions have been made for $R_{A} (x, Q^{2})$ in the kinematic region of $x$ and $Q^{2}$ for some nuclei relevant for the future experiments to be performed at the JLab.
↳ hep-phnucl-th3 citations
07
Particle production in proton-nucleus collisions beyond leading order
E. Iancu🇫🇷 · A.H. Mueller🇺🇸 · D.N. Triantafyllopoulos🇮🇹
We describe the origin of, and the solution to, the negativity problem which occurs in the perturbative calculation of the cross-section for single-inclusive particle production in proton-nucleus collisions at next-to-leading-order.
↳ hep-phnucl-thNPA(2017)·0 citations
08
Landau levels in QCD
F. Bruckmann🇩🇪 · G. Endrodi🇩🇪 · M. Giordano🇭🇺 · S. D. Katz🇭🇺 · T. G. Kovacs🇭🇺 · F. Pittler🇭🇺 · J. Wellnhofer🇩🇪
We present first evidence for the Landau level structure of Dirac eigenmodes in full QCD for nonzero background magnetic fields, based on first principles lattice simulations using staggered quarks. Our approach involves the identification of the lowest Landau level modes in two dimensions, where topological arguments ensure a clear separation of these modes from energetically higher states, and an expansion of the full four-dimensional modes in the basis of these two-dimensional states. We evaluate various fermionic observables including the quark condensate and the spin polarization in this basis to find how much the lowest Landau level contributes to them. The results allow for a deeper insight into the dynamics of quarks and gluons in background magnetic fields and may be directly compared to low-energy models of QCD employing the lowest Landau level approximation.
↳ hep-lathep-phhep-thnucl-thPRD(2017)·61 citations

Affiliations

first authorsco-authorsvia INSPIRE