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Title Transverse charge and current densities in the nucleon from dispersively improved chiral effective field theory
Authors Christian Weiss
JLAB number JLAB-THY-22-3606
LANL number arXiv:2204.11863
Other number DOE/OR/23177-5480
Document Type(s) (Journal Article) 
Associated with EIC: No
Supported by Jefferson Lab LDRD Funding: No
Funding Source: Nuclear Physics (NP)

Compiled for Physical Review C
Publication Abstract: Background: The transverse densities rho_{1, 2}(b) describe the distributions of electric charge and magnetic moment at fixed light-front time and connect the nucleon's elastic form factors with its partonic structure. The dispersive representation of the form factors F_{1, 2}(t) expresses the densities in terms of exchanges of hadronic states in the t-channel and permits their analysis using hadronic physics methods. Purpose: Compute the densities at peripheral distances b = O(M_pi^{-1}), where they are generated predominantly by the two-pion states in the dispersive representation. Quantify the uncertainties. Methods: Dispersively improved chiral effective field theory (DIXEFT) is used to calculate the isovector spectral functions Im F_{1, 2}(t) on the two-pion cut. The method includes pi-pi interactions (rho resonance) through elastic unitarity and provides realistic spectral functions up to t ~ 1 GeV^2. Higher-mass states are parametrized by effective poles and constrained by sum rules (charges, radii, superconvergence relations). The densities rho_{1, 2}(b) are obtained from their dispersive representation. Uncertainties are quantified by varying the spectral functions. The method respects analyticity and ensures the correct b -> infinity asymptotic behavior of the densities. Results: Accurate densities are obtained at all distances b >~ 0.5 fm, with correct behavior down to b -> 0. The region of distances is quantified where transverse nucleon structure is governed by the two-pion state. The light-front current distributions in the polarized nucleon are computed and discussed. Conclusions: Peripheral nucleon structure can be computed from first principles using DIXEFT. The method can be extended to generalized parton distributions and other nucleon form factors.
Experiment Numbers: other
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