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Nuclear Theory·nucl-th

Thursday·October 13, 2016

7 papers—2 primary·5 cross-listed

All7Primary2Cross-lists5
  1. 01

    [Submitted on 12 Oct 2016]

    Nuclear axial current operators to fourth order in chiral effective field theory

    H. Krebs🇩🇪 · E. Epelbaum🇩🇪 · U.-G. Meißner🇩🇪

    We present the complete derivation of the nuclear axial charge and current operators as well as the pseudoscalar operators to fourth order in the chiral expansion relative to the dominant one-body contribution using the method of unitary transformation. We demonstrate that the unitary ambiguity in the resulting operators can be eliminated by the requirement of renormalizability and by matching of the pion-pole contributions to the nuclear forces. We give expressions for the renormalized single-, two- and three-nucleon contributions to the charge and current operators and pseudoscalar operators including the relevant relativistic corrections. We also verify explicitly the validity of the continuity equation.

    Comments:
    72 pages, 21 figures, 3 tables
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1610.03569 [pdf]
    Annals Phys.(2017)·109 citations
  2. 02

    [Submitted on 12 Oct 2016]

    The Effect of Quantum Fluctuations in the High-Energy Cold Nuclear Equation of State and in Compact Star Observables

    Péter Pósfay🇭🇺 · Gergely Gábor Barnaföldi🇭🇺 · Antal Jakovác🇭🇺

    We present a novel technique to obtain exact equation of state (EoS) by the Functional Renormalization Group (FRG) method, using the expansion of the effective potential in a base of harmonic functions at finite chemical potential. Within this theoretical framework we determined the equation of state and the phase diagram of a simple model of massless fermions coupled to scalars through Yukawa-coupling at the zero-temperature limit. We compared our results to the 1-loop and the mean field approximation of the same model and other high-density nuclear matter equation of states. We found a difference between these approximations. As an application, we used our exact, FRG-based equation of states to test the effect of the quantum fluctuations in superdense nuclear matter of a compact astrophysical object for the first time. We calculated the mass-radius relation for a compact star using the Tolmann-Oppenheimer-Volkov equation and observed a effect in compact star observables due to quantum fluctuations.

    Comments:
    4 pages, 4 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1610.03674 [pdf]
    PRC(2018)·8 citations
  3. 03

    [Submitted on 11 Oct 2016] (cross-list from hep-th)

    Nonperturbative solution of scalar Yukawa model in two- and three-body Fock space truncations

    Vladimir A. Karmanov🇷🇺 · Yang Li🇺🇸 · Alexander V. Smirnov🇷🇺 · James P. Vary🇺🇸

    The Light-Front Tamm-Dancoff method of finding the nonperturbative solutions in field theory is based on the Fock decomposition of the state vector, complemented with the sector-dependent nonperturbative renormalization scheme. We show in detail how to implement the renormalization procedure and to solve the simplest nontrivial example of the scalar Yukawa model in the two- and three-body Fock space truncations incorporating scalar "nucleon" and one or two scalar "pions".

    Comments:
    34 pages, 16 figures, submitted to Phys. Rev. D
    Subjects:
    High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    1610.03559 [pdf]
    PRD(2016)·17 citations
  4. 04

    [Submitted on 12 Oct 2016] (cross-list from nucl-ex)

    Symmetry energy and density

    Wolfgang Trautmann🇩🇪 · Mircea Dan Cozma🇷🇴 · Paolo Russotto🇮🇹

    The nuclear equation-of-state is a topic of highest current interest in nuclear structure and reactions as well as in astrophysics. In particular, the equation-of-state of asymmetric matter and the symmetry energy representing the difference between the energy densities of neutron matter and of symmetric nuclear matter are not sufficiently well constrained at present. The density dependence of the symmetry energy is conventionally expressed in the form of the slope parameter L describing the derivative with respect to density of the symmetry energy at saturation. Results deduced from nuclear structure and heavy-ion reaction data are distributed around a mean value L=60 MeV. Recent studies have more thoroughly investigated the density range that a particular observable is predominantly sensitive to. Two thirds of the saturation density is a value typical for the information contained in nuclear-structure data. Higher values exceeding saturation have been shown to be probed with meson production and collective flows at incident energies in the range of up to about 1 GeV/nucleon. From the measurement of the elliptic-flow ratio of neutrons with respect to light charged particles in recent experiments at the GSI laboratory, a new more stringent constraint for the symmetry energy at suprasaturation density has been deduced. It confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence of the symmetry energy previously deduced from the FOPI-LAND data. Future opportunities offered by FAIR will be discussed.

    Comments:
    10 pages, 4 figures, talk presented at the 54th International Winter Meeting on Nuclear Physics, 25-29 January 2016, Bormio, Italy
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1610.03650 [pdf]
    PoS(2016)·2 citations
  5. 05

    [Submitted on 12 Oct 2016] (cross-list from hep-ph)

    Plasmon mass scale in classical nonequilibrium gauge theory

    Tuomas Lappi🇫🇮 · Jarkko Peuron🇫🇮

    Classical lattice Yang-Mills calculations provide a good way to understand different nonequilibrium phenomena in nonperturbatively overoccupied systems. Above the Debye scale the classical theory can be matched smoothly to kinetic theory. The aim of this work is to study the limits of this quasiparticle picture by determining the plasmon mass in classical real time Yang-Mills theory on a lattice in 3 spatial dimensions. We compare three methods to determine the plasmon mass: a hard thermal loop expression in terms of the particle distribution, an effective dispersion relation constructed from fields and their time derivatives, and by measuring oscillations between electric and magnetic field modes after artificially introducing a homogeneous color electric field. We find that a version of the dispersion relation that uses electric fields and their time derivatives agrees with the other methods within 50%.

    Comments:
    9 pages, 10 figures, to appear in Phys. Rev. D
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1610.03711 [pdf]
    PRD(2017)·16 citations
  6. 06

    [Submitted on 11 Oct 2016] (cross-list from nucl-ex)

    Measurement of the ratio of the sixth order to the second order cumulant of net-proton multiplicity distributions in relativistic heavy-ion collisions

    Lizhu Chen🇨🇳 · Zhiming Li🇨🇳 · Fenping Cui🇨🇳 · Yuanfang Wu🇨🇳

    We investigate the measurement of the sixth order cumulant and its ratio to the second order cumulant () in relativistic heavy-ion collisions. The influence of statistics and different methods of centrality bin width correction on of net-proton multiplicity distributions is demonstrated. There is no satisfactory method to extract with the current statistics recorded at lower energies by STAR at RHIC. With statistics comparable to the expected statistics at the planned future RHIC Beam Energy Scan II (BES II), no energy dependence of is observed in central collisions using the UrQMD model. We find if the transition signal is as strong as predicted by the PQM model, then it is hopefully observed at the upcoming RHIC BES II.

    Subjects:
    Nuclear Experiment (nucl-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1610.03781 [pdf]
    NPA(2017)·9 citations
  7. 07

    [Submitted on 12 Oct 2016] (cross-list from hep-th)

    Spectral and thermodynamic properties of the Sachdev-Ye-Kitaev model

    Antonio M. García-García🇬🇧 · Jacobus J. M. Verbaarschot🇺🇸

    We study spectral and thermodynamic properties of the Sachdev-Ye-Kitaev model, a variant of the -body embedded random ensembles studied for several decades in the context of nuclear physics and quantum chaos. We show analytically that the fourth and sixth order energy cumulants vanish in the limit of large number of particles which is consistent with a Gaussian spectral density. However, for finite , the tail of the average spectral density is well approximated by a semi-circle law. The specific heat coefficient, determined numerically from the low temperature behavior of the partition function, is consistent with the value obtained by previous analytical calculations. For energy scales of the order of the mean level spacing we show that level statistics are well described by random matrix theory. Due to the underlying Clifford algebra of the model, the universality class of the spectral correlations depends on . For larger energy separations we identify an energy scale that grows with , reminiscent of the Thouless energy in mesoscopic physics, where deviations from random matrix theory are observed. Our results are a further confirmation that the Sachdev-Ye-Kitaev model is quantum chaotic for all time scales. According to recent claims in the literature, this is an expected feature in field theories with a gravity-dual.

    Comments:
    29 pages, 11 figures, journal version
    Subjects:
    High Energy Physics — Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Nuclear Theory (nucl-th)
    arXiv:
    1610.03816 [pdf]
    PRD(2016)·355 citations

Affiliations

first authorsco-authorsvia INSPIRE