Spin of the proton in chiral effective field theory

Abstract

Proton spin is investigated in chiral effective field theory through an examination of the singlet axial charge, a0, and the two non-singlet axial charges, a3 and a8. Finite-range regularization is considered as it provides an effective model for estimating the role of disconnected sea-quark loop contributions to baryon observables. Baryon octet and decuplet intermediate states are included to enrich the spin and flavour structure of the nucleon, redistributing spin under the constraints of chiral symmetry. In this context, the proton spin puzzle is well understood with the calculation describing all three of the axial charges reasonably well. The strange quark contribution to the proton spin is negative with magnitude 0.01. With appropriate Q 2 evolution, we find the singlet axial charge at the experimental scale to beâ0 = 0.31 +0.04 −0.05 , consistent with the range of current experimental values.

Electromagnetic form factors of octet baryons with the nonlocal chiral effective theory

“…An alternative regularization method, namely finite-range regularization (FRR) has been proposed. Inspired by quark models that account for the finite-size of the nucleon as the source of the pion cloud, effective field theory with FRR has been widely applied to extrapolate lattice data of vector meson mass, magnetic moments, magnetic form factors, strange form factors, charge radii, first moments of GPDs, nucleon spin, etc., [15][16][17][18][19][20][21][22][23][24].…”

Strange form factors of the nucleon with a nonlocal chiral effective Lagrangian

“…When vector mesons are included, the result is close to the experiments with Q 2 less than 0.4 GeV 2 [21].An alternative regularization method, namely finite-range-regularization (FRR) has been proposed. Inspired by quark models that account for the finite-size of the nucleon as the source of the pion cloud, effective field theory with FRR has been widely applied to extrapolate the vector meson mass, magnetic moments, magnetic form factors, strange form factors, charge radii, first moments of GPDs, nucleon spin, etc [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. In the finite-range-regularization, there is no cut for the energy integral.…”

Pauli form factors of electron and muon in nonlocal quantum electrodynamics

“…We should mention that the regulator is not introduced phenomenologically to deal with the divergence. This is different from the original finite-range-regularization [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. The regulator is naturally generated from the nonlocal Lagrangian with the naive idea that the interaction between photon and lepton does not necessary take place at one point.…”