Nuclear Theory·nucl-th

Friday·December 19, 2014

11 papers—2 primary·9 cross-listed

01
Hyperon Puzzle of Neutron Stars with Skyrme Force Models
Yeunhwan Lim🇰🇷 · Chang Ho Hyun🇰🇷 · Kyujin Kwak🇰🇷 · Chang-Hwan Lee🇰🇷
We consider the so called hyperon puzzle of neutron star (NS). We employ Skyrme force models for the description of in-medium nucleon-nucleon, nucleon-Lambda hyperon ( $N Λ$ ), and Lambda-Lambda ( $ΛΛ$ ) interactions. A phenomenological finite-range force for the $ΛΛ$ interaction is considered as well. Equation of state (EoS) of NS matter is obtained in the framework of density functional theory, and Tolman-Oppenheimer-Volkoff equations are solved to obtain the mass-radius relations of NSs. It has been generally known that the existence of hyperons in the NS matter is not well supported by the recent discovery of large-mass NSs ( $M ≃ 2 M_{⊙}$ ) since hyperons make the EoS softer than the one without them. For the selected interaction models, $N Λ$ interactions reduce the maximum mass of NS by about 30~\%, while $ΛΛ$ interactions can give about 10~\% enhancement. Consequently, we find that some Skyrme force models predict the maximum mass of NS consistent with the observation of $2 M_{⊙}$ NSs, and at the same time satisfy observationally constrained mass-radius relations.
nucl-thastro-ph.SRhep-phIJMPE(2015)·42 citations
02
UrQMD Study of the Effects of Centrality Definitions on Higher Moments of Net Protons at RHIC
Gary D. Westfall🇺🇸
A study using UrQMD is presented concerning the higher moments of net protons from Au+Au collisions at 7.7, 11.5, 14.6, 19.6, 27, 39, 62.4, and 200 GeV, concentrating on $C_{4} / C_{2} = κ σ^{2}$ . Higher moments of net protons are predicted to be a sensitive probe of the critical point of QCD. At the QCD critical point, particular ratios of the moments of net protons are predicted to differ from the Poisson baseline. Recently STAR has published the higher moments of net protons for Au+Au collisions at $s_{NN}$ = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV. UrQMD quantitatively reproduces STAR's measured $C_{4} / C_{2} = κ σ^{2}$ for net protons for all Au+Au collisions more central than 30\% and at all centralities for $s_{NN}$ = 7.7 and 11.5 GeV. The effects are investigated of three different centrality definitions on the values of $C_{4} / C_{2} = κ σ^{2}$ from UrQMD calculations including the impact parameter given by UrQMD. It is shown that using a centrality definition based on multiplicity to calculate the higher moments of net protons gives a biased answer for $C_{4} / C_{2} = κ σ^{2}$ , except in the most central bin (0-5\%).
nucl-thnucl-exPRC(2015)·17 citations
03
The interplay of disk wind and dynamical ejecta in the aftermath of neutron star - black hole mergers
Rodrigo Fernández🇺🇸 · Eliot Quataert🇺🇸 · Josiah Schwab🇺🇸 · Daniel Kasen🇺🇸 · Stephan Rosswog🇸🇪
We explore the evolution of the different ejecta components generated during the merger of a neutron star (NS) and a black hole (BH). Our focus is the interplay between material ejected dynamically during the merger, and the wind launched on a viscous timescale by the remnant accretion disk. These components are expected to contribute to an electromagnetic transient and to produce r-process elements, each with a different signature when considered separately. Here we introduce a two-step approach to investigate their combined evolution, using two- and three-dimensional hydrodynamic simulations. Starting from the output of a merger simulation, we identify each component in the initial condition based on its phase space distribution, and evolve the accretion disk in axisymmetry. The wind blown from this disk is injected into a three-dimensional computational domain where the dynamical ejecta is evolved. We find that the wind can suppress fallback accretion on timescales longer than ~100 ms. Due to self-similar viscous evolution, the disk accretion at late times nevertheless approaches a power-law time dependence $\propto t^{- 2.2}$ . This can power some late-time GRB engine activity, although the available energy is significantly less than in traditional fallback models. Inclusion of radioactive heating due to the r-process does not significantly affect the fallback accretion rate or the disk wind. We do not find any significant modification to the wind properties at large radius due to interaction with the dynamical ejecta. This is a consequence of the different expansion velocities of the two components.
↳ astro-ph.HEastro-ph.SRgr-qcnucl-thMNRAS(2015)·96 citations
04
Holographic Heavy Quark Symmetry
Koji Hashimoto🇯🇵 · Noriaki Ogawa🇯🇵 · Yasuhiro Yamaguchi🇯🇵
We investigate the heavy quark spin symmetry, i.e. the mass degeneracy of pseudo-scalar and vector quarkonia at heavy quark limit, by using the gauge/gravity correspondence. We allow generic D3-like geometry with a flavor D7-brane, to avoid supersymmetric mass degeneracy. For geometries admitting physical QCD-like properties, we find that the mass degeneracy is generically achieved in a good accuracy, up to a few percent mass splitting. We also compute spectra of excited quarkonia states, and discuss comparisons with experiments and quark-model calculations.
↳ hep-thhep-phnucl-thJHEP(2015)·19 citations
05
Energy spectra of two interacting fermions with spin-orbit coupling in a harmonic trap
Cory D. Schillaci · Thomas C. Luu
We explore the two-body spectra of spin- $1/2$ fermions in isotropic harmonic traps with external spin-orbit potentials and short range two-body interactions. Using a truncated basis of total angular momentum eigenstates, non-perturbative results are presented for experimentally realistic forms of the spin-orbit coupling: a pure Rashba coupling, Rashba and Dresselhaus couplings in equal parts, and a Weyl-type coupling. The technique is easily adapted to bosonic systems and other forms of spin-orbit coupling.
↳ cond-mat.quant-gasnucl-thPRA(2015)·6 citations
06
Thermodynamics of heavy-light hadrons
Heng-Tong Ding (for the BNL-Bielefeld-CCNU collaboration)🇨🇳
Ratios of cumulants of conserved net charge fluctuations are sensitive to the degrees of freedom that are carriers of the corresponding quantum numbers in different phases of strong interaction matter. We calculate second and fourth order cumulants of net charm and strange fluctuations and their correlations with other conserved charges such as net baryon number and electric charge. Simulation are performed on $N_{τ}$ =6 and 8 lattices using the Highly Improved Staggered Quark (HISQ) action with a light to strange quark mass ratio of 1/20 and having charm quarks treated in the quenched approximation. Analysing appropriate ratios of these cumulants we observe that both open strange and charm hadrons start to get dissociated in the chiral crossover region. We provide indirect evidence for the existence of additional, experimentally yet unobserved open charm and strange hadrons from QCD thermodynamics. This is done by comparing lattice QCD results to Hadron Resonance Gas (HRG) model calculations performed with a hadron spectrum as listed in the Particle Data Tables as well as with a spectrum predicted in the relativistic quark model and observed in lattice QCD calculations. We also discuss the influence of these experimentally yet unobserved states on the determination of freeze-out temperature and chemical potentials from heavy ion collision experiments. We found that including these additional states in the HRG model leads to a systematic 5-8 MeV decrease in the freeze-out temperature of strange hadrons.
↳ hep-lathep-phnucl-thPoS(2014)·3 citations
07
Unified Description of Classical and Quantum Behaviours in a Variational Principle
Tomoi Koide🇧🇷 · Takeshi Kodama🇧🇷 · Kazuo Tsushima🇧🇷
We give a pedagogical introduction of the stochastic variational method and show that this generalized variational principle describes classical and quantum mechanics in a unified way.
↳ quant-phgr-qchep-thnucl-thJ.Phys.Conf.Ser.(2015)·15 citations
08
Impact of the energy loss spatial profile and shear viscosity to entropy density ratio for the Mach cone vs. head shock signals produced by a fast moving parton in a quark-gluon plasma
Alejandro Ayala🇿🇦 · Jorge David Castano-Yepes🇲🇽 · Isabel Dominguez🇲🇽 · Maria Elena Tejeda-Yeomans🇲🇽
We compute the energy and momentum deposited by a fast moving parton in a quark-gluon plasma using linear viscous hydrodynamics with an energy loss per unit length profile proportional to the path length and with different values of the shear viscosity to entropy density ratio. We show that when varying these parameters, the transverse modes still dominate over the longitudinal ones and thus energy and momentum is preferentially deposited along the head-shock, as in the case of a constant energy loss per unit length profile and the lowest value for the shear viscosity to entropy density ratio.
↳ hep-phnucl-thPRC(2015)·6 citations
09
Accelerating Ab Initio Nuclear Physics Calculations with GPUs
Hugh Potter · Dossay Oryspayev · Pieter Maris · Masha Sosonkina · James Vary · Sven Binder · Angelo Calci · Joachim Langhammer · Robert Roth · Ümit Çatalyürek · Erik Saule
This paper describes some applications of GPU acceleration in ab initio nuclear structure calculations. Specifically, we discuss GPU acceleration of the software package MFDn, a parallel nuclear structure eigensolver. We modify the matrix construction stage to run partly on the GPU. On the Titan supercomputer at the Oak Ridge Leadership Computing Facility, this produces a speedup of approximately 2.2x - 2.7x for the matrix construction stage and 1.2x - 1.4x for the entire run.
↳ physics.comp-phnucl-thProc. 'Nuclear Theory in the Supercomputi…·0 citations
10
Delayed Magnetic Catalysis
Jens Braun🇩🇪 · Walid Ahmed Mian🇩🇪 · Stefan Rechenberger🇩🇪
We study the effect of an external magnetic field on the chiral phase transition in the theory of the strong interaction by means of a renormalization-group (RG) fixed-point analysis, relying on only one physical input parameter, the strong coupling at a given large momentum scale. To be specific, we consider the interplay of the RG flow of four-quark interactions and the running gauge coupling. Depending on the temperature and the strength of the magnetic field, the gauge coupling can drive the quark sector to criticality, resulting in chiral symmetry breaking. In accordance with lattice Monte-Carlo simulations, we find that the chiral phase transition temperature decreases for small values of the external magnetic field. For large magnetic field strengths, however, our fixed-point study predicts that the phase transition temperature increases monotonically.
↳ hep-phcond-mat.str-elhep-latnucl-thPLB(2016)·82 citations
11
Nuclear structure aspects of spin-independent WIMP scattering off xenon
L. Vietze🇩🇪 · P. Klos🇩🇪 · J. Menéndez🇩🇪 · W. C. Haxton🇺🇸 · A. Schwenk🇩🇪
We study the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations, which are shown to yield a good spectroscopic description of all experimentally relevant isotopes. Our results are based on the leading scalar one-body currents only. At this level and for the momentum transfers relevant to direct dark matter detection, the structure factors are in very good agreement with the phenomenological Helm form factors used to give experimental limits for WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the spin-independent channel, at the one-body level, is less sensitive to nuclear structure details. In addition, we explicitly show that the structure factors for inelastic scattering are suppressed by ~ 10^{-4} compared to the coherent elastic scattering response. This implies that the detection of inelastic scattering will be able to discriminate clearly between spin-independent and spin-dependent scattering. Finally, we provide fits for all calculated structure factors.
↳ nucl-thastro-ph.COhep-phPRD(2015)·124 citations

Affiliations

first authorsco-authorsvia INSPIRE