Nuclear Theory·nucl-th

Thursday·February 28, 2019

9 papers—3 primary·6 cross-listed

04
[Submitted on 26 Feb 2019] (cross-list from hep-ph)
Quark mass dependence of $γ^{*} π \to π π$
Malwin Niehus🇩🇪 · Martin Hoferichter🇺🇸 · Bastian Kubis🇩🇪
Usually the simulation of scattering processes in lattice QCD is carried out at unphysically high values of the quark masses. Hence, a method to extrapolate data obtained in lattice calculations to physical masses is needed to allow for comparison between theory and experiment. To obtain a sound extrapolation, dispersion relations and chiral perturbation theory can be invoked. While a simple combined approach known as the inverse amplitude method allows for a successful extrapolation of $π π \to π π$ data, a more complicated framework is needed for inelastic processes such as $γ^{*} π \to π π$ . By employing a well-established dispersive description, the extrapolation can be performed for $γ^{*} π \to π π$ both for on-shell as well as virtual photons, the decay $γ^{*} \to π π π$ is also within the range of applicability. This particular process is interesting due to both its contribution to the anomalous magnetic moment of the muon and its connection to the axial anomaly.
Comments:
10 pages, 2 figures, proceedings for The 9th International Workshop on Chiral Dynamics, Durham, North Carolina, USA, September 17-21, 2018
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1902.10150 [pdf]
PoS(2019)·13 citations
05
[Submitted on 26 Feb 2019] (cross-list from hep-ph)
Electromagnetic multipole moments of baryons
Alfons J. Buchmann🇩🇪
We calculate the charge quadrupole and magnetic octupole moments of baryons using a group theoretical approach based on broken SU(6) spin-flavor symmetry. The latter is an approximate symmetry of the QCD Lagrangian which becomes exact in the large color N_c limit. Spin-flavor symmetry breaking is induced by one-, two-, and three-quark terms in the electromagnetic current operator. Two- and three-quark currents provide the leading contributions for higher multipole moments, despite being of higher order in an 1/N_c expansion. Our formalism leads to relations between N --> N* transition multipole moments and nucleon ground state properties. We compare our results to experimental quadrupole and octupole transition moments extracted from measured helicity amplitudes.
Comments:
18 pages, 8 figures, Talk given at NSTAR 2017, 11th International Workshop on the Physics of Excited Nucleons, Aug. 20-23, 2017, Columbia, SC, USA
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1902.10166 [pdf]
Few Body Syst.(2018)·9 citations
06
[Submitted on 27 Feb 2019] (cross-list from hep-lat)
Constraints on Disconnected Contributions in $π π$ Scattering
N. Ripunjay Acharya🇩🇪 · Feng-Kun Guo🇨🇳 · Ulf-G. Meißner🇩🇪 · Chien-Yeah Seng🇩🇪
The accuracy of the lattice QCD computation of hadron-hadron scattering at low isospin depends critically on the ability to compute correlation functions with fermionic disconnected Wick contractions. This happens, for instance, in isospin $I = 0$ $π π$ scattering, which receives contributions from rectangular and vacuum types of contractions among other easier calculable ones. Combining Lüscher's formula and partially-quenched chiral perturbation theory, we provide precise theory predictions of the discrete energy levels extracted from specific linear combinations of lattice correlation functions corresponding to various types of contractions. Expressions are provided for extracting the unphysical low-energy constants in the partially-quenched chiral perturbation theory from the energy levels for these contractions. The predictions for the rectangular and vacuum contractions may serve as solid tests of the accuracy for existing and future lattice studies of $π π$ scattering.
Comments:
Version to appear in JHEP
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1902.10290 [pdf]
JHEP(2019)·6 citations
07
[Submitted on 27 Feb 2019] (cross-list from hep-ph)
Aspects of quarkonium propagation in a thermal medium as seen by string models
Oleg Andreev🇷🇺
We use gauge/string duality to model a heavy quark-antiquark pair in a color singlet moving through a thermal plasma. In particular, we explore the effect of velocity on the string tension and Debye screening mass. Then we apply the results to the analysis of heavy quarkonium bound states. With some assumptions, we estimate the characteristic size of quarkonium and its dissociation temperature.
Comments:
17 pages, 8 figures; v2: improved presentation and discussion, typos corrected, references added
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1902.10458 [pdf]
PRD(2019)·4 citations
08
[Submitted on 27 Feb 2019] (cross-list from hep-ph)
Flavor decomposition of the pion-nucleon $σ$ -term
Daniel Severt🇩🇪 · Ulf-G. Meißner🇩🇪 · Jambul Gegelia🇬🇪
We re-analyze the flavor decomposition of the pion-nucleon $σ$ -term in the framework of baryon chiral perturbation to fourth order. We employ a covariant and the heavy baryon framework including also the low-lying decuplet. Using only continuum data, we find a small strangeness content of the proton. The uncertainties are, however, large and might be overcome by dedicated lattice QCD calculations.
Comments:
31 pages, 1 figure, published version, some minor modifications
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1902.10508 [pdf]
JHEP(2019)·12 citations
09
[Submitted on 27 Feb 2019] (cross-list from nucl-ex)
Exposing Novel Quark and Gluon Effects in Nuclei
I. C. Cloët🇺🇸 · R. Dupré🇫🇷 · S. Riordan🇺🇸 · W. Armstrong🇺🇸 · J. Arrington🇺🇸 · W. Cosyn🇧🇪 · N. Fomin🇺🇸 · A. Freese🇺🇸 · S. Fucini🇮🇹 · D. Gaskell🇺🇸 · C. E. Keppel🇺🇸 · G. A. Miller🇺🇸 and 6 other authors
The fundamental theory of the strong interaction -- quantum chromodynamics (QCD) -- provides the foundational framework with which to describe and understand the key properties of atomic nuclei. A deep understanding of the explicit role of quarks and gluons in nuclei remains elusive however, as these effects have thus far been well-disguised by confinement effects in QCD which are encapsulated by a successful description in terms of effective hadronic degrees of freedom. The observation of the EMC effect has provided an enduring indication for explicit QCD effects in nuclei, and points to the medium modification of the bound protons and neutrons in the nuclear medium. Understanding the EMC effect is a major challenge for modern nuclear physics, and several key questions remain, such as understanding its flavor, spin, and momentum dependence. This manuscript provides a contemporary snapshot of our understanding of the role of QCD in nuclei and outlines possible pathways in experiment and theory that will help deepen our understanding of nuclei in the context of QCD.
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1902.10572 [pdf]
J.Phys.G(2019)·38 citations

Affiliations

first authorsco-authorsvia INSPIRE

Quark mass dependence of γ∗π→ππ

Electromagnetic multipole moments of baryons

Constraints on Disconnected Contributions in ππ Scattering

Aspects of quarkonium propagation in a thermal medium as seen by string models

Flavor decomposition of the pion-nucleon σ-term

Exposing Novel Quark and Gluon Effects in Nuclei

Affiliations

Quark mass dependence of $γ^{*} π \to π π$

Constraints on Disconnected Contributions in $π π$ Scattering

Flavor decomposition of the pion-nucleon $σ$ -term