Nuclear Theory·nucl-th

Wednesday·November 3, 2021

8 papers—4 primary·4 cross-listed

05
[Submitted on 1 Nov 2021] (cross-list from hep-lat)
$b ˉ c ˉ q_{1} q_{2}$ four-quark states from Lattice QCD
M. Padmanath🇮🇳 · Nilmani Mathur🇩🇪
We present the results of a lattice calculation of four-quark states with the quark contents $b ˉ c ˉ q_{1} q_{2}$ where $q_{1}, q_{2} \in u, d, s$ . For the spin 1 states, when the light quark ( $q_{1}, q_{2}$ ) masses are lighter, we find at least one energy level below the possible elastic threshold energy levels. These calculations are performed on three dynamical $N_{f} = 2 + 1 + 1$ highly improved staggered quark ensembles at lattice spacings of about 0.12, 0.09, and 0.06 fm. We use the overlap action for light to charm quarks while a non-relativistic action with non-perturbatively improved coefficients is employed for the bottom quark.
Comments:
9 pages, 6 figures. Proceedings of the 38th International Symposium on Lattice Field Theory (LATTICE2021)
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2111.01147 [pdf]
PoS(2022)·17 citations
06
[Submitted on 1 Nov 2021] (cross-list from hep-ph)
Positivity and renormalization of parton densities
John Collins🇺🇸 · Ted C. Rogers🇺🇸 · Nobuo Sato🇺🇸
There have been recent debates about whether $MS$ parton densities exactly obey positivity bounds (including the Soffer bound), and whether the bounds should be applied as a constraint on global fits to parton densities and on nonperturbative calculations. A recent paper (JHEP $11$ (2020) 129) appears to provide a proof of positivity in contradiction with earlier work by other authors. We examine their derivation and find that its primary failure is in the apparently uncontroversial statement that bare pdfs are always positive. We show that under the conditions used in the derivation, that statement fails. We provide some elementary calculations in a model QFT that show how this situation can generically arise in reality. In addition, we observe that the methods used in the derivation are in common with much, but not all, other work where factorization is derived. Our examination pinpoints considerable difficulties with these methods that render them either wrong or highly problematic. The issue of positivity highlights that these methods can lead to wrong results of phenomenological importance. From our analysis we identify the restricted situations in which positivity can be violated.
Comments:
24 pages, 3 figures, version published in physical review D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2111.01170 [pdf]
PRD(2022)·59 citations
07
[Submitted on 2 Nov 2021] (cross-list from hep-ph)
The $η$ - and $η^{'}$ -nucleus interactions and the search for $η$ , $η^{'}$ - mesic states
Steven D. Bass🇦🇹 · Volker Metag🇩🇪 · Pawel Moskal🇵🇱
The isoscalar $η$ and $η^{'}$ mesons are special in QCD, being linked both to chiral symmetry and to non-perturbative glue associated with the axial anomaly. The properties of these mesons in medium are sensitive to how these dynamics work in the nuclear environment. In contrast to pionic and kaonic atoms which are mainly bound by the Coulomb interaction with some corrections due to the strong force (Coulomb assisted binding), the $η$ and $η^{'}$ as neutral mesons can only be bound by the strong interaction. Is this interaction strong enough? This topic has inspired a vigorous program of experiments, conducted in close contact with theory, One has to determine the complex $η$ , $η^{'}$ -nucleus potential. Does the real part $V$ provide a sufficiently deep potential? Is the imaginary part $W$ small enough to allow for narrow states that can more easily be detected experimentally, i.e. $∣ W ∣ ≪ ∣ V ∣$ ? The $η^{'}$ effective mass is observed to be suppressed by $\approx - 40$ MeV at nuclear matter density. Bound state searches are ongoing. This article gives an overview of the status of knowledge in this field together with an outlook to future experiments.
Comments:
26 pages, 12 figures. arXiv admin note: text overlap with arXiv:1810.12290
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2111.01388 [pdf]
In: Tanihata, I., Toki, H., Kajino, T. (e…·11 citations
08
[Submitted on 2 Nov 2021] (cross-list from hep-ph)
Hadronic structure on the light-front II: QCD strings, Wilson lines and potentials
Edward Shuryak🇺🇸 · Ismail Zahed🇺🇸
This is the second paper on hadronic wave functions in the light front formulation. We first consider only confinement effects, using the classical Nambu-Gotto string with massive end points in the light cone gauge. We derive the light-front Hamiltonian and show how to solve it, using an expansion in suitable basis functions. We next discuss the correlators of Wilson lines on the light front, leading to an effective Hamiltonian that includes spin effects. At the end, we consider a separate problem of instanton-induced interactions, at the origin of the pion as a massless Goldstone mode on the light front.
Comments:
31 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2111.01775 [pdf]
PRD(2023)·23 citations

Affiliations

first authorsco-authorsvia INSPIRE

bˉcˉq1​q2​four-quark states from Lattice QCD

Positivity and renormalization of parton densities

The η- and η′-nucleus interactions and the search for η, η′- mesic states

Hadronic structure on the light-front II: QCD strings, Wilson lines and potentials

Affiliations

$b ˉ c ˉ q_{1} q_{2}$ four-quark states from Lattice QCD

The $η$ - and $η^{'}$ -nucleus interactions and the search for $η$ , $η^{'}$ - mesic states