Gernot Eichmann
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View article: The anomalous magnetic moment of the muon in the Standard Model: an update
The anomalous magnetic moment of the muon in the Standard Model: an update Open
We present the current Standard Model (SM) prediction for the muon anomalous magnetic moment, $a_μ$, updating the first White Paper (WP20) [1]. The pure QED and electroweak contributions have been further consolidated, while hadronic contr…
View article: Timelike form factor for the anomalous process γ⁎π → ππ
Timelike form factor for the anomalous process γ⁎π → ππ Open
The form factor $F_{3π}(s,t,u)$ for the anomalous process $γ^\ast π\rightarrow ππ$ is calculated in the isospin limit for several values of the light current-quark mass (i.e., the pion mass) using Dyson-Schwinger and Bethe-Salpeter equatio…
View article: Five-point functions and the permutation group <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>S</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math>
Five-point functions and the permutation group Open
Five-point functions and five-body wave functions play an important role in many areas of nuclear and particle physics, e.g., in 2→3 scattering processes, in the five-gluon vertex, or in the study of pentaquarks. In this work we consider t…
View article: Axial-vector and scalar contributions to hadronic light-by-light scattering
Axial-vector and scalar contributions to hadronic light-by-light scattering Open
We present results for single axial-vector and scalar meson pole contributions to the hadronic light-by-light scattering (HLbL) part of the muon’s anomalous magnetic moment. In the dispersive approach to these quantities (in narrow width a…
View article: Functional methods for hadron spectroscopy
Functional methods for hadron spectroscopy Open
We summarize recent results for four-quark states with hidden and open flavor obtained from a four-quark Bethe-Salpeter/Faddeev-Yakubowsky equation. The approach dynamically predicts the leading internal two-body clusters such as meson-mes…
View article: Structure of open-flavor four-quark states in the charm and bottom region
Structure of open-flavor four-quark states in the charm and bottom region Open
We present quantitative results for masses and the internal structure of four-quark states with two heavy quarks, i.e., QQ′q¯q¯′ with Q,Q′∈{c,b} and q,q′∈{u,d,s}, and JP∈1+. The composition of these states in terms of meson-meson and diqua…
View article: Hadron physics with functional methods
Hadron physics with functional methods Open
We give a pedagogical introduction to hadron spectroscopy and structure studies using functional methods. We explain the basic features of Dyson-Schwinger, Bethe-Salpeter and Faddeev equations, which are employed to calculate the spectra o…
View article: Five-body systems with Bethe-Salpeter equations
Five-body systems with Bethe-Salpeter equations Open
We extend the Bethe-Salpeter formalism to systems made of five valence particles. Restricting ourselves to two-body interactions, we derive the subtraction terms necessary to prevent overcounting. We solve the five-body Bethe-Salpeter equa…
View article: Five-point functions and the permutation group S5
Five-point functions and the permutation group S5 Open
Five-point functions and five-body wave functions play an important role in many areas of nuclear and particle physics, e.g., in 2 -> 3 scattering processes, in the five-gluon vertex, or in the study of pentaquarks. In this work we conside…
View article: Axial-vector and scalar contributions to hadronic light-by-light scattering
Axial-vector and scalar contributions to hadronic light-by-light scattering Open
We present results for single axial-vector and scalar meson pole contributions to the hadronic light-by-light scattering (HLbL) part of the muon's anomalous magnetic moment. In the dispersive approach to these quantities (in narrow width a…
View article: Structure of open-flavour four-quark states in the charm and bottom region
Structure of open-flavour four-quark states in the charm and bottom region Open
We present quantitative results for masses and the internal structure of four-quark states with two heavy quarks, i.e. $QQ'\bar{q}\bar{q}'$ with $Q,Q'\in \{c,b\}$ and $q,q' \in \{u,d,s\}$, and $J^{P} \in {1^+}$. The composition of these st…
View article: Bound states from the spectral Bethe-Salpeter equation
Bound states from the spectral Bethe-Salpeter equation Open
We compute the bound state properties of three-dimensional scalar ϕ4 theory in the broken phase. To this end, we extend the recently developed technique of spectral Dyson-Schwinger equations to solve the Bethe-Salpeter equation and determi…
View article: Bound states from the spectral Bethe-Salpeter equation
Bound states from the spectral Bethe-Salpeter equation Open
We compute the bound state properties of three-dimensional scalar $ϕ^4$ theory in the broken phase. To this end, we extend the recently developed technique of spectral Dyson-Schwinger equations to solve the Bethe-Salpeter equation and dete…
View article: The case for an EIC Theory Alliance: Theoretical Challenges of the EIC
The case for an EIC Theory Alliance: Theoretical Challenges of the EIC Open
We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spe…
View article: Heavy baryon spectroscopy in a quark-diquark approach
Heavy baryon spectroscopy in a quark-diquark approach Open
We report progress on calculations of the heavy-light baryons $Σ_c$ and $Λ_c$ and their excitations with $J^P = 1/2^+$ using functional methods. We employ a covariant quark-diquark approach, where the interaction amounts to a quark exchang…
View article: The Case for an EIC Theory Alliance
The Case for an EIC Theory Alliance Open
This documents outlines the case for the creation of an EIC Theory Alliance. The EIC will be a unique and versatile facility that will enable the understanding of some of the most compelling questions in the physics of the strong nuclear f…
View article: Studying mass generation for gluons
Studying mass generation for gluons Open
In covariant gauges, the gluonic mass gap in Yang-Mills theory manifests itself in the basic observation that the massless pole in the perturbative gluon propagator disappears in nonperturbative calculations, but the origin of this behavio…
View article: Report on 2112.08058v1
Report on 2112.08058v1 Open
In covariant gauges, the gluonic mass gap in Yang-Mills theory manifests itself in the basic observation that the massless pole in the perturbative gluon propagator disappears in nonperturbative calculations, but the origin of this behavio…
View article: Going to the light front with contour deformations
Going to the light front with contour deformations Open
We explore a new method to calculate the valence light-front wave function of\na system of two interacting particles, which is based on contour deformations\ncombined with analytic continuation methods to project the Bethe-Salpeter wave\nf…
View article: Studying mass generation for gluons
Studying mass generation for gluons Open
In covariant gauges, the gluonic mass gap in Yang-Mills theory manifests itself in the basic observation that the massless pole in the perturbative gluon propagator disappears in nonperturbative calculations, but the origin of this behavio…
View article: Mass generation in Landau-gauge Yang-Mills theory
Mass generation in Landau-gauge Yang-Mills theory Open
A longstanding question in QCD is the origin of the mass gap in the Yang-Mills sector of QCD, i.e., QCD without quarks. In Landau gauge QCD this mass gap, and hence confinement, is encoded in a mass gap of the gluon propagator, which is fo…
View article: Going to the light front with contour deformations
Going to the light front with contour deformations Open
We explore a new method to calculate the valence light-front wave function of a system of two interacting particles, which is based on contour deformations combined with analytic continuation methods to project the Bethe-Salpeter wave func…
View article: Reply to comment on "The $\sigma$-meson: four-quark vs. two-quark components and decay width in a Bethe-Salpeter approach"
Reply to comment on "The $\sigma$-meson: four-quark vs. two-quark components and decay width in a Bethe-Salpeter approach" Open
In a recent comment [1] Blankleider and Kvinikhidze claim that our work [2] is based on a set of inconsistent Bethe-Salpeter equations for the coupling of four-quark to two-quark states. Here we demonstrate that their argument is insubstan…
View article: Reply to comment on "The $σ$-meson: four-quark vs. two-quark components and decay width in a Bethe-Salpeter approach"
Reply to comment on "The $σ$-meson: four-quark vs. two-quark components and decay width in a Bethe-Salpeter approach" Open
In a recent comment [1] Blankleider and Kvinikhidze claim that our work [2] is based on a set of inconsistent Bethe-Salpeter equations for the coupling of four-quark to two-quark states. Here we demonstrate that their argument is insubstan…
View article: Disentangling different structures in heavy-light four-quark states
Disentangling different structures in heavy-light four-quark states Open
Models proposed to explain recently discovered heavy-light four-quark states already assume certain internal structures, i.e. the (anti)quark constituents are grouped into diquark/antidiquark clusters, heavy-meson/light-meson clusters (had…