Nuclear Theory·nucl-th

Tuesday·August 30, 2016

16 papers—7 primary·9 cross-listed

08
[Submitted on 26 Aug 2016] (cross-list from hep-ph)
Baryons in the unquenched quark model
R. Bijker🇲🇽 · S. Diaz-Gomez🇲🇽 · M.A. Lopez-Ruiz🇺🇸 · E. Santopinto🇮🇹
In this contribution, we present the unquenched quark model as an extension of the constituent quark model that includes the effects of sea quarks via a $^{3} P_{0}$ quark-antiquark pair-creation mechanism. Particular attention is paid to the spin and flavor content of the proton, magnetic moments and $β$ decays of octet baryons.
Comments:
5 pages, 1 figure, 2 tables, invited talk XI LASNPA, Medellin, Colombia
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1608.07629 [pdf]
AIP Conf.Proc.(2016)·1 citation
09
[Submitted on 27 Aug 2016] (cross-list from hep-ph)
Reconstructing parton densities at large fractional momenta
Alessandro Bacchetta🇮🇹 · Marco Radici🇮🇹 · Barbara Pasquini🇮🇹 · Xiaonu Xiong🇮🇹
Parton distribution functions (PDFs) are nonperturbative objects defined by nonlocal light-cone correlations. They cannot be computed directly from Quantum Chromodynamics (QCD). Using a standard lattice QCD approach, it is possible to compute moments of PDFs, which are matrix elements of local operators. Recently, an alternative approach has been proposed, based on the introduction of quasi-parton distribution functions (quasi-PDFs), which are matrix elements of equal-time spatial correlations and hence calculable on lattice. Quasi-PDFs approach standard PDFs in the limit of very large longitudinal proton momenta $P^{z}$ . This limit is not attainable in lattice simulations, and quasi-PDFs fail to reproduce PDFs at high fractional longitudinal momenta. In this paper, we propose a method to improve the reconstruction of PDFs by combining information from quasi-PDFs and from the Mellin moments of regular PDFs. We test our method using the diquark spectator model for up and down valence distributions of both unpolarized and helicity PDFs. In the future, the method can be used to produce PDFs entirely based on lattice QCD results.
Comments:
12 pages, 7 double-panel figures in pdf, RevTeX4-1
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1608.07638 [pdf]
PRD(2017)·20 citations
10
[Submitted on 27 Aug 2016] (cross-list from hep-ph)
Lagrangian magnetic moment from polarization
Fabio L. Braghin🇧🇷
An effective Lagrangian term for the electron magnetic moment, and more generally electromagnetic form factors, is calculated by considering the background field method. Two Fierz transformations are performed for a one-photon exchange interaction, and the ambiguity in doing such transformations is exploited. The resulting effective interaction may exhibit an approximated rotational chiral symmetry either for the scalar-pseudoscalar currents interaction or for the vector-axial currents interaction. The leading terms in the expansion of the fermion determinant yield the leading QED effective action with the complete one loop electromagnetic form factors. A model is proposed to produce the tree level magnetic moment term.
Comments:
Withdrawn due to a mistake in the calculation
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1608.07733 [pdf]
0 citations
11
[Submitted on 28 Aug 2016] (cross-list from hep-ph)
The axial charges of the hidden-charm pentaquark states
Guang-Juan Wang🇨🇳 · Zhan-Wei Liu🇦🇺 · Shi-Lin Zhu🇨🇳
With the chiral quark model, we have calculated the axial charges of the pentaquark states with $(I, I_{3}) = (\frac{1}{2}, \frac{1}{2})$ and $J^{P} = \frac{1}{2}^{\pm}, \frac{3}{2}^{\pm}, \frac{5}{2}^{\pm}$ . The $P_{c}$ states with the same $J^{P}$ quantum numbers but different color-spin-flavor configurations have very different axial charges, which encode important information on their underlying structures. For some of the $J^{P} = \frac{3}{2}^{\pm}$ or $\frac{5}{2}^{\pm}$ pentaquark states, their axial charges are much smaller than that of the proton.
Comments:
13 pages
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1608.07824 [pdf]
PRC(2016)·3 citations
12
[Submitted on 28 Aug 2016] (cross-list from nucl-ex)
Longitudinal Wobbling in $^{133}$ La
S. Biswas · R. Palit · S. Frauendorf · U. Garg · W. Li · G.H. Bhat · J.A. Sheikh · J. Sethi · S. Saha · Purnima Singh · D. Choudhury · J.T. Matta and 4 other authors
Excited states of $^{133}$ La have been investigated to search for the wobbling excitation mode in the low-spin regime. Wobbling bands with $n_{ω}$ = 0 and 1 are identified along with the interconnecting $Δ I$ = 1, $E 2$ transitions, which are regarded as one of the characteristic features of the wobbling motion. An increase in wobbling frequency with spin implies longitudinal wobbling for $^{133}$ La, in contrast with the case of transverse wobbling observed in $^{135}$ Pr. This is the first observation of a longitudinal wobbling band in nuclei. The experimental observations are accounted for by calculations using the quasiparticle-triaxial-rotor (QTR) model, which attribute the appearance of longitudinal wobbling to the early alignment of a $π = +$ proton pair.
Comments:
9 pages, 6 figures, 1 table
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1608.07840 [pdf]
EPJA(2019)·75 citations
13
[Submitted on 29 Aug 2016] (cross-list from hep-ph)
Universal limiting pressure for a three-flavor color superconducting PNJL model phase diagram
A. Ayriyan🇷🇺 · J. Berdermann🇩🇪 · D. Blaschke🇵🇱 · R. Lastowiecki🇵🇱
The phase diagram of a three-flavor Polyakov-loop Nambu-Jona-Lasinio model is analyzed for the case of isospin symmetric matter with color superconducting phases. The coexistence of chiral symmetry breaking and two-flavor color superconductivity (2SC phase) and a thermodynamic instability due to the implementation of a color neutrality constraint is observed. It is suggested to use a universal hadronization pressure to estimate the phase border between hadronic and quark-gluon plasma phases. Trajectories of constant entropy per baryon are analyzed for conditions appropriate for heavy-ion collisions in the NICA-FAIR energy range.
Comments:
6 pages, 3 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1608.07875 [pdf]
3 citations
14
[Submitted on 29 Aug 2016] (cross-list from hep-ph)
$X (4140)$ , $X (4270)$ , $X (4500)$ and $X (4700)$ and their $cs c ˉ s ˉ$ tetraquark partners
Jing Wu🇨🇳 · Yan-Rui Liu🇨🇳 · Kan Chen🇨🇳 · Xiang Liu🇨🇳 · Shi-Lin Zhu🇨🇳
In the simple color-magnetic interaction model, we investigate possible ground $cs c ˉ s ˉ$ tetraquark states in the diquark-antidiquark basis. We use several methods to estimate the mass spectrum and discuss possible assignment for the $X$ states observed in the $J / ψ ϕ$ channel. We find that assigning the Belle $X (4350)$ as a $0^{++}$ tetraquark is consistent with the tetraquark interpretation for the $X (4140)$ and $X (4270)$ while the interpretation of the $X (4500)$ and $X (4700)$ needs orbital or radial excitation. There probably exist several tetraquarks around 4.3 GeV that decay into $J / ψ ϕ$ or $η_{c} ϕ$ .
Comments:
Publication version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1608.07900 [pdf]
PRD(2016)·69 citations
15
[Submitted on 29 Aug 2016] (cross-list from hep-ph)
Color screening masses from string models
Oleg Andreev🇷🇺
We use gauge/string duality to estimate the Debye screening mass at non-zero temperature and baryon chemical potential. We interpret this mass as the smallest one in the open string channel. Comparisons are made with the results from holography and lattice QCD.
Comments:
26 pages, many figures; v2: presentation improved, typos corrected
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1608.08026 [pdf]
PRD(2016)·11 citations
16
[Submitted on 29 Aug 2016] (cross-list from hep-ph)
Covariant Spectator Theory of heavy-light and heavy mesons and the predictive power of covariant interaction kernels
Sofia Leitão🇵🇹 · Alfred Stadler🇵🇹 · M. T. Peña🇵🇹 · Elmar P. Biernat🇵🇹
The Covariant Spectator Theory (CST) is used to calculate the mass spectrum and vertex functions of heavy-light and heavy mesons in Minkowski space. The covariant kernel contains Lorentz scalar, pseudoscalar, and vector contributions. The numerical calculations are performed in momentum space, where special care is taken to treat the strong singularities present in the confining kernel. The observed meson spectrum is very well reproduced after fitting a small number of model parameters. Remarkably, a fit to a few pseudoscalar meson states only, which are insensitive to spin-orbit and tensor forces and do not allow to separate the spin-spin from the central interaction, leads to essentially the same model parameters as a more general fit. This demonstrates that the covariance of the chosen interaction kernel is responsible for the very accurate prediction of the spin-dependent quark-antiquark interactions.
Comments:
5 pages, 2 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1608.08065 [pdf]
PLB(2017)·19 citations

Affiliations

first authorsco-authorsvia INSPIRE