On extraction of twist-two Compton form factors from DVCS observables through harmonic analysis

Shiells, Kyle; Guo, Yuxun; Ji, Xiangdong

doi:10.1007/jhep08(2022)048

Cited by 7 publications

(2 citation statements)

References 68 publications

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“…Ideally, one would need all 8 possible combinations of P b and P t to disentangle the 8 CFFs, see for instance ref. [61], but there could still be degeneracy in the solutions as the nature of quadratic equations. In this work, the degeneracy will be more severe, since only two polarization configurations, unpolarized or polarized beam with unpolarized target (UU and LU), are considered.…”

Section: Jhep05(2023)150mentioning

confidence: 99%

Generalized parton distributions through universal moment parameterization: non-zero skewness case

Guo

Santiago³

et al. 2023

J. High Energ. Phys.

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We present the first global analysis of generalized parton distributions (GPDs) combing lattice quantum chromodynamics (QCD) calculations and experiment measurements including global parton distribution functions (PDFs), form factors (FFs) and deeply virtual Compton scattering (DVCS) measurements. Following the previous work where we parameterize GPDs in terms of their moments, we extend the framework to allow for the global analysis at non-zero skewness. Together with the constraints at zero skewness, we fit GPDs to global DVCS measurements from both the recent JLab and the earlier Hadron-Electron Ring Accelerator (HERA) experiments with two active quark flavors and leading order QCD evolution. With certain choices of empirical constraints, both sea and valence quark distributions are extracted with the combined inputs, and we present the quark distributions in the proton correspondingly. We also discuss how to extend the framework to accommodate more off-forward constraints beyond the small ξ expansion, especially the lattice calculated GPDs.

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Section: Jhep05(2023)150mentioning

confidence: 99%

Generalized parton distributions through universal moment parameterization: non-zero skewness case

Guo

Santiago³

et al. 2023

J. High Energ. Phys.

Self Cite

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“…( 4)-( 8) [16,[40][41][42]. The first step in this procedure is to obtain the CFFs from DVCS data, which at leading twist is a closed problem [18] and several leading-twist CFF extractions have been reported in the literature [43][44][45][46][47][48]. The challenge of extracting GPDs from the CFFs lies in the fact that the 𝑥 dependence of the GPDs is completely integrated out and does not appear in the CFFs.…”

Section: Cffs Gpds and Sgpdsmentioning

confidence: 99%

Shedding light on shadow generalized parton distributions

Moffat¹,

Freese²,

Cloët³

et al. 2023

Preprint

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The feasibility of extracting generalized parton distributions (GPDs) from deeply-virtual Compton scattering (DVCS) data has recently been questioned because of the existence of an infinite set of so-called "shadow GPDs" (SGPDs). These SGPDs depend on the process and manifest as multiple solutions (at a fixed scale 𝑄 2 ) to the inverse problem that needs to be solved to infer GPDs from DVCS data. SGPDs therefore pose a significant challenge for extracting GPDs from DVCS data. With this motivation we study the extent to which QCD evolution can provide constraints on SGPDs. This is possible because the known classes of SGPDs begin to contribute to observables after evolution, and can then be constrained (at the input scale 𝑄 2 0 ) by data that has a finite 𝑄 2 range. The impact that SGPDs could have on determining the total angular momentum, pressure and sheer force distributions, and tomography is also discussed. Our key finding is that scale evolution, coupled with data over a wide range of skewness 𝜉 and 𝑄 2 , can constrain the class of SGPDs that we studied and potentially make possible the extraction of GPDs from DVCS data over a limited range in the GPD variables.

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Looking at QED with Dyson–Schwinger Equations: Basic Equations, Ward–Takahashi Identities and the Two-Photon-Two-Fermion Irreducible Vertex

2023

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A minimal truncated set of the integral Dyson–Schwinger equations, in Minkowski spacetime, that allows to explore QED beyond its perturbative solution is derived for general linear covariant gauges. The minimal set includes the equations for the fermion and photon propagators, the photon-fermion vertex, and the two-photon-two-fermion one-particle-irreducible diagram. If the first three equations are exact, to build a closed set of equations, the two-photon-two-fermion equation is truncated ignoring the contribution of Green functions with large number of external legs. It is shown that the truncated equation for the two-photon-two-fermion vertex reproduces the lowest-order perturbative result in the limit of the small coupling constant. Furthermore, this equation allows to define an iterative procedure to compute higher order corrections in the coupling constant. The Ward–Takahashi identity for the two-photon-two-fermion irreducible vertex is derived and solved in the soft photon limit, where one of the photon momenta vanish, in the low photon momenta limit and for general kinematics. The solution of the Ward–Takahashi identity determines the longitudinal component of the two-photon-two-fermion irreducible vertex, while it is proposed to use the Dyson–Schwinger equation to determine the transverse part of this irreducible diagram. The two-photon-two-fermion DSE is solved in heavy fermion limit, considering a simplified version of the QED vertices. The contribution of this irreducible vertex to a low-energy effective photon-fermion vertex is discussed and the fermionic operators that are generated are computed in terms of the fermion propagator functions.

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On extraction of twist-two Compton form factors from DVCS observables through harmonic analysis

Abstract: We investigate the exercise of locally extracting the real and imaginary parts of the four twist-2 Compton form factors (CFFs) $$ \left\{\mathcal{H},\mathcal{E},\overset{\sim }{\mathcal{H}},\overset{\sim }{\mathcal{E}}\right\} $$ H E H ~ E ~ which … Show more

Cited by 7 publications

References 68 publications

Generalized parton distributions through universal moment parameterization: non-zero skewness case

Generalized parton distributions through universal moment parameterization: non-zero skewness case

Shedding light on shadow generalized parton distributions

Looking at QED with Dyson–Schwinger Equations: Basic Equations, Ward–Takahashi Identities and the Two-Photon-Two-Fermion Irreducible Vertex

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