Nuclear Theory·nucl-th

Thursday·May 18, 2017

11 papers—3 primary·8 cross-listed

04
[Submitted on 9 May 2017] (cross-list from hep-ph)
Fate of in-medium heavy quarks via a Lindblad equation
Davide De Boni🇬🇧
What is the dynamics of heavy quarks and antiquarks in a quark gluon plasma? Can heavy-quark bound states dissociate? Can they (re)combine? These questions are addressed by investigating a Lindblad equation that describes the quantum dynamics of the heavy quarks in a medium. The Lindblad equations for a heavy quark and a heavy quark-antiquark pair are derived from the gauge theory, following a chain of well-defined approximations. In this work the case of an abelian plasma has been considered, but the extension to the non-abelian case is feasible. A one-dimensional simulation of the Lindblad equation is performed to extract information about bound-state dissociation, recombination and quantum decoherence for a heavy quark-antiquark pair. All these phenomena are found to depend strongly on the imaginary part of the inter-quark potential.
Comments:
50 pages, 10 figures - added references - corrected typos and added a few comments - added appendix D
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1705.03567 [pdf]
JHEP(2017)·43 citations
05
[Submitted on 13 May 2017] (cross-list from hep-ph)
Jet Quenching at RHIC and LHC and the Fragmentation Function in Vacuum
Gouranga C Nayak🇺🇸
The value of the parton to hadron fragmentation function in QCD in vacuum (for example from proton-proton collisions at high energy colliders) is directly/indirectly used in the literature to study the jet quenching and the hadron production from quark-gluon plasma at RHIC and LHC. In this paper we show that this is not possible because, unlike the perturbative propagator in non-equilibrium QCD, the parton to hadron fragmentation function is a non-perturbative quantity in QCD and hence it is not possible to decompose the fragmentation function in non-equilibrium QCD into the vacuum part and the medium part.
Comments:
18 pages latex
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1705.04878 [pdf]
11 citations
06
[Submitted on 16 May 2017] (cross-list from hep-lat)
Sea Quarks Contribution to the Nucleon Magnetic Moment and Charge Radius at the Physical Point
Raza Sabbir Sufian🇺🇸 · Yi-Bo Yang🇺🇸 · Jian Liang🇺🇸 · Terrence Draper🇺🇸 · Keh-Fei Liu🇺🇸
We report a comprehensive analysis of the light and strange disconnected-sea quarks contribution to the nucleon magnetic moment, charge radius, and the electric and magnetic form factors. The lattice QCD calculation includes ensembles across several lattice volumes and lattice spacings with one of the ensembles at the physical pion mass. We adopt a model-independent extrapolation of the nucleon magnetic moment and the charge radius. We have performed a simultaneous chiral, infinite volume, and continuum extrapolation in a global fit to calculate results in the continuum limit. We find that the combined light and strange disconnected-sea quarks contribution to the nucleon magnetic moment is $μ_{M} (DI) = - 0.022 (11) (09) μ_{N}$ and to the nucleon mean square charge radius is $⟨ r^{2} ⟩_{E} (DI) = - 0.019 (05) (05)$ fm $^{2}$ which is about $1/3$ of the difference between the $⟨ r_{p}^{2} ⟩_{E}$ of electron-proton scattering and that of muonic atom and so cannot be ignored in obtaining the proton charge radius in the lattice QCD calculation. The most important outcome of this lattice QCD calculation is that while the combined light-sea and strange quarks contribution to the nucleon magnetic moment is small at about $1%$ , a negative $2.5 (9) %$ contribution to the proton mean square charge radius and a relatively larger positive $16.3 (6.1) %$ contribution to the neutron mean square charge radius come from the sea quarks in the nucleon. For the first time, by performing global fits, we also give predictions of the light and strange disconnected-sea quarks contributions to the nucleon electric and magnetic form factors at the physical point and in the continuum and infinite volume limits in the momentum transfer range of $0 \leq Q^{2} \leq 0.5$ GeV $^{2}$ .
Comments:
Published Version, 26 pages, 8 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1705.05849 [pdf]
PRD(2017)·25 citations
07
[Submitted on 16 May 2017] (cross-list from hep-ph)
First simultaneous extraction of spin-dependent parton distributions and fragmentation functions from a global QCD analysis
J. J. Ethier🇺🇸 · N. Sato🇺🇸 · W. Melnitchouk🇺🇸
We perform the first global QCD analysis of polarized inclusive and semi-inclusive deep-inelastic scattering and single-inclusive $e^{+} e^{-}$ annihilation data, fitting simultaneously the parton distribution and fragmentation functions using the iterative Monte Carlo method. Without imposing SU(3) symmetry relations, we find the strange polarization to be very small, consistent with zero for both inclusive and semi-inclusive data, which provides a resolution to the strange quark polarization puzzle. The combined analysis also allows the direct extraction from data of the isovector and octet axial charges, and is consistent with a small SU(2) flavor asymmetry of the polarized sea.
Comments:
5 pages, 4 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1705.05889 [pdf]
PRL(2017)·256 citations
08
[Submitted on 16 May 2017] (cross-list from hep-ph)
Low energy constituent quark and pion effective couplings in a weak external magnetic field
Fábio L. Braghin🇧🇷
An effective model with pions and constituent quarks in the presence of a weak external background electromagnetic field is derived by starting from a dressed one gluon exchange quark-quark interaction.By applying the auxiliary field and background field methods, the structureless pion limit is considered to extract effective pion and constituent quark couplings in the presence of a weak magnetic field. The leading terms of a large quark and gluon masses expansion are obtained by resolving effective coupling constants which turn out to depend on a weak magnetic field. Two pion field definitions are considered for that. Several relations between the effective coupling constants and parameters can be derived exactly or in the limit of very large quark mass at zero and weak constant magnetic field. Among these ratios, the Gell Mann Oakes Renner and the quark level Goldberger Treiman relations are obtained. In addition to that, in the pion sector, the leading terms of Chiral Perturbation Theory coupled to the electromagnetic field is recovered. Some numerical estimates are provided for the effective coupling constants and parameters.
Comments:
26 pages, revised and improved version with numerical estimates. To be published in Eur.Phys. Journ. A (2018)
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1705.05926 [pdf]
EPJA(2018)·19 citations
09
[Submitted on 17 May 2017] (cross-list from hep-th)
Fluctuations in quantum mechanics and field theories from a new version of semiclassical theory. II
M.A. Escobar-Ruiz🇺🇸 · E. Shuryak🇺🇸 · A.V. Turbiner🇺🇸
This is the second paper on semiclassical approach based on the density matrix given by the Euclidean time path integral with fixed coinciding endpoints. The classical path, interpolating between this point and the classical vacuum, called "flucton", plus systematic one- and two-loop corrections, has been calculated in the first paper \cite{Escobar-Ruiz:2016aqv} for double-well potential and now extended for a number of quantum-mechanical problems (anharmonic oscillator, sine-Gordon potential). The method is based on systematic expansion in Feynman diagrams and thus can be extended to QFTs. We show that the loop expansion in QM reminds the leading log-approximations in QFT. In this sequel we present complete set of results obtained using this method in unified way. Alternatively, starting from the Schrödinger equation we derive a {\it generalized} Bloch equation which semiclassical-like, iterative solution generates the loop expansion. We re-derive two loop expansions for all three above potentials and now extend it to three loops, which has not yet been done via Feynman diagrams. All results for both methods are fully consistent with each other. Asymmetric (tilted) double-well potential (non-degenerate minima) is also studied using the second method.
Subjects:
High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
1705.06159 [pdf]
PRD(2017)·11 citations
10
[Submitted on 17 May 2017] (cross-list from hep-ph)
Comparison of two Minkowski-space approaches to heavy quarkonia
Sofia Leitão🇵🇹 · Yang Li🇺🇸 · Pieter Maris🇺🇸 · M. T. Peña🇵🇹 · Alfred Stadler🇵🇹 · James P. Vary🇺🇸 · Elmar P. Biernat🇵🇹
In this work we compare mass spectra and decay constants obtained from two recent, independent, and fully relativistic approaches to the quarkonium bound-state problem: the Hamiltonian basis light-front quantization (BLFQ) approach, where light-front wave functions are naturally formulated; and, the covariant spectator theory (CST), based on a reorganization of the Bethe-Salpeter equation. Even though conceptually different, both solutions are obtained in Minkowski space. Comparisons of decay constants for more than ten states of charmonium and bottomonium show favorable agreement between the two approaches as well as with experiment where available. We also apply the Brodsky-Huang-Lepage prescription to convert the CST amplitudes into functions of light-front variables. This provides an ideal opportunity to investigate the similarities and differences at the level of the wave functions. Several qualitative features are observed in remarkable agreement between the two approaches even for the rarely addressed excited states. Leading twist distribution amplitudes as well as parton distribution functions of heavy quarkonia are also analyzed.
Comments:
16 pages
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1705.06178 [pdf]
EPJC(2017)·33 citations
11
[Submitted on 17 May 2017] (cross-list from hep-lat)
Iso-vector axial form factors of the nucleon in two-flavour lattice QCD
Stefano Capitani🇩🇪 · Michele Della Morte🇩🇰 · Dalibor Djukanovic🇩🇪 · Georg M. von Hippel🇩🇪 · Jiayu Hua🇩🇪 · Benjamin Jäger🇬🇧 · Parikshit M. Junnarkar🇮🇳 · Harvey B. Meyer🇩🇪 · Thomas D. Rae🇩🇪 · Hartmut Wittig🇩🇪
We present a lattice calculation of the nucleon iso-vector axial and induced pseudoscalar form factors on the CLS ensembles using $N_{f} = 2$ dynamical flavours of non-perturbatively $O (a)$ -improved Wilson fermions and an $O (a)$ -improved axial current together with the pseudoscalar density. Excited-state effects in the extraction of the form factors are treated using a variety of methods, with a detailed discussion of their respective merits. The chiral and continuum extrapolation of the results is performed both using formulae inspired by Heavy Baryon Chiral Perturbation Theory (HBChPT) and a global approach to the form factors based on a chiral effective theory (EFT) including axial vector mesons. Our results indicate that careful treatment of excited-state effects is important in order to obtain reliable results for the axial form factors of the nucleon, and that the main remaining error stems from the systematic uncertainties of the chiral extrapolation. As final results, we quote $g_{A} = 1.278 \pm 0.068 - 0.087 + 0.000$ , $⟨ r_{A}^{2} ⟩ = 0.360 \pm 0.036 - 0.088 + 0.080 fm^{2}$ , and $g_{P} = 7.7 \pm 1.8 - 2.0 + 0.8$ for the axial charge, axial charge radius and induced pseudoscalar charge, respectively, where the first error is statistical and the second is systematic.
Comments:
27 pages, 13 figures (23 PDF files); uses revtex4-1.cls; v4: corrections to affiliation addresses, matches published version
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1705.06186 [pdf]
Int.J.Mod.Phys.A(2019)·98 citations

Affiliations

first authorsco-authorsvia INSPIRE