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Nuclear Theory·nucl-th

Monday·May 6, 2019

6 papers—1 primary·5 cross-listed

All6Primary1Cross-lists5
  1. 02

    [Submitted on 3 May 2019] (cross-list from astro-ph.HE)

    Effective repulsion in dense quark matter from non-perturbative gluon exchange

    Yifan Song🇺🇸 · Gordon Baym🇺🇸 · Tetsuo Hatsuda🇯🇵 · Toru Kojo🇨🇳

    A moderately strong vector repulsion between quarks in dense quark matter is needed to explain how a quark core can support neutron stars heavier than two solar masses. We study this repulsion, parametrized by a four-fermion interaction with coupling g_V, in terms of non-perturbative gluon exchange in QCD in the Landau gauge. Matching the energy of quark matter, g_V n_q^2 (where n_q is the number density of quarks) with the quark exchange energy calculated in QCD with a gluon propagator parametrized by a finite gluon mass m_g and a frozen coupling alpha_s, at moderate quark densities, we find that gluon masses m_g in the range 200 - 600 MeV and alpha_s = 2 - 4 lead to a g_V consistent with neutron star phenomenology. Estimating the effects of quark masses and a color-flavor-locked (CFL) pairing gap, we find that g_V can be well approximated by a flavor-symmetric, decreasing function of density. We briefly discuss similar matchings for the isovector repulsion and for the pairing attraction.

    Comments:
    9 pages, 6 figures
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1905.01005 [pdf]
    PRD(2019)·46 citations
  2. 03

    [Submitted on 3 May 2019] (cross-list from hep-ph)

    QCD equation of state at finite baryon density with fugacity expansion

    Volodymyr Vovchenko🇩🇪 · Jan Steinheimer🇩🇪 · Owe Philipsen🇩🇪 · Horst Stoecker🇩🇪

    We explore the QCD equation of state at finite baryon density through an expansion in baryon number fugacity, making use of the recent lattice data on the four leading Fourier coefficients of the expansion. A state-of-the-art description of the lattice data at both imaginary and is provided by the cluster expansion model (CEM). The CEM pressure function has three temperature dependent input parameters, which we fix by parameterizing the available lattice QCD data. This results in a crossover model of the QCD equation of state at finite baryon density, which can be used in fluid dynamical simulations of heavy-ion collisions.

    Comments:
    8 pages, 4 figures. Contribution to the proceedings of the CPOD2018 conference, Corfu Island, Greece, September 24-28, 2018
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1905.01031 [pdf]
    PoS(2019)·6 citations
  3. 04

    [Submitted on 3 May 2019] (cross-list from nucl-ex)

    Effects of resonance weak decays and hadronic re-scattering on the proton number fluctuations in Au + Au collisions at GeV from JAM model

    Yu Zhang🇨🇳 · Shu He🇨🇳 · Hui Liu🇨🇳 · Zhenzhen Yang🇨🇳 · Xiaofeng Luo🇨🇳

    Proton number fluctuation is sensitive observable to search for the QCD critical point in heavy-ion collisions. In this paper, we studied rapidity acceptance dependence of the proton cumulants and correlation functions in most central Au+Au collisions at GeV from a microscopic hadronic transport model (JAM). At mid-rapidity, we found the effects of resonance weak decays and hadronic re-scattering on the proton cumulants and correlation functions are small, but those effects get larger when further increasing the rapidity acceptance. On the other hand, we found the baryon number conservation is a dominant background effect on the rapidity acceptance dependence of proton number fluctuations. It leads to a strong suppression of cumulants and cumulant ratios, as well as the negative proton correlation functions. We also studied those two effects on the energy dependence of cumulant ratios of net-proton distributions in most central Au+Au collisions at GeV from JAM model. This work can serve as a non-critical baseline for future QCD critical point search in heavy-ion collisions at high baryon density region.

    Comments:
    8 pages, 7 figures, To be published in Physical Review C
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1905.01095 [pdf]
    PRC(2020)·13 citations
  4. 05

    [Submitted on 3 May 2019] (cross-list from astro-ph.HE)

    Combined Rastall and Rainbow theories of gravity with applications to neutron stars

    Clésio E. Mota🇧🇷 · Luis C. N. Santos🇧🇷 · Guilherme Grams🇧🇷 · Franciele M. da Silva🇧🇷 · Débora P. Menezes🇧🇷

    The possibility of modifications on general relativity is investigated. We propose an alternative theory of gravity constructed with the combination of Rastall and Rainbow theories. The hydrostatic equilibrium equations are obtained in order to test the new theory in neutron stars, whose mass-radius diagrams are obtained using modern equations of state of nuclear matter derived from relativistic mean field models and compared with the ones computed by the Tolman-Oppenheimer-Volkoff equations. We conclude that substantial modifications are obtained even for very small alterations on the two free parameters, making the reproduction of astrophysical observations an easy task.

    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
    arXiv:
    1905.01250 [pdf]
    PRD(2019)·68 citations
  5. 06

    [Submitted on 3 May 2019] (cross-list from hep-lat)

    Nucleon isovector charges and twist-2 matrix elements with dynamical Wilson quarks

    Tim Harris🇩🇪 · Georg von Hippel🇩🇪 · Parikshit Junnarkar🇩🇪 · Harvey B. Meyer🇩🇪 · Konstantin Ottnad🇩🇪 · Jonas Wilhelm🇩🇪 · Hartmut Wittig🇩🇪 · Linus Wrang🇩🇪

    We present results from a lattice QCD study of nucleon matrix elements at vanishing momentum transfer for local and twist-2 isovector operator insertions. Computations are performed on gauge ensembles with non-perturbatively improved Wilson fermions, covering four values of the lattice spacing and pion masses down to MeV. Several source-sink separations (typically ~1.0fm to ~1.5fm) allow us to assess excited-state contamination. Results on individual ensembles are obtained from simultaneous two-state fits across all observables and all available source-sink separations with the energy gap as a common fit parameter. Renormalization has been performed non-perturbatively using the Rome-Southampton method for all but the finest lattice spacing for which an extrapolation has been used. Physical results are quoted in the scheme at a scale of GeV and are obtained from a combined chiral, continuum and finite-size extrapolation. For the nucleon isovector axial, scalar and tensor charges we find physical values of , and , respectively, where individual systematic errors in each direction from the chiral, continuum and finite-size extrapolation have been added in quadrature. Our final results for the isovector average quark momentum fraction and the isovector helicity and transversity moments are given by , and , respectively.

    Comments:
    35 pages, 13 figures; matching version accepted for publication in PRD
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1905.01291 [pdf]
    PRD(2019)·93 citations

Affiliations

first authorsco-authorsvia INSPIRE