Δ(1232) Electroproduction Amplitudes in Chiral Soliton Models of the Nucleon (original) (raw)
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The electroproduction of the Δ(1232) in the chiral quark–soliton model
Nuclear Physics A, 2000
We calculate the ratios E2/M1 and C2/M1 for the electroproduction of the ∆(1232) in the region of photon virtuality 0 <−q 2 < 1 GeV 2. The magnetic dipole amplitude M1 is also presented. The theory used is the chiral quark-soliton model, which is based on the instanton vacuum of the QCD. The calculations are performed in flavours SU(2) and SU(3) taking rotational (1/N c) corrections into account. The results for the ratios agree qualitatively with the available data, although the magnitude of both ratios seems to underestimate the latest experimental results.
Chiral effective-field theory in the Delta(1232) region: Pion electroproduction on the nucleon
Physical Review D, 2006
We develop an extension of chiral perturbation theory to the Delta\DeltaDelta(1232)-resonance energy region and apply it to investigate the pion electroproduction off the nucleon ($e^- N \to e^- N\pi$). We present a complete calculation of this process, in the Delta\DeltaDelta-resonance region, up to next-to-leading order in the {\it delta\deltadelta-expansion}. At this order, the only free parameters are the three low-energy constants corresponding to the magnetic (M1), electric (E2), and Coulomb (C2) gammaNtoDelta\gamma N \to \Delta gammaNtoDelta transition strength. After fitting these parameters to a few well-known data, our calculation provides a prediction for observables and multipole amplitudes of pion electroproduction. These results compare favorably with the phenomenological multipole solutions and recent experimental results from MIT-Bates and MAMI. Our prediction for the pion-mass dependence of the gammaNDelta\gamma N\DeltagammaNDelta form factors offers an explanation for the discrepancy between the recent lattice-QCD results and the experimental value for the "C2/M1 ratio" at low Q2Q^2Q2.
Axial amplitudes for Δ excitation in chiral quark models
Physics Letters B, 2003
We study the axial amplitudes for the N-∆ transition in models with quarks and chiral mesons. A set of constraints on the pion field is imposed which enforces PCAC and the off-diagonal Goldberger-Treiman relation. The quark contribution to the amplitudes in general strongly underestimates the C A 5 amplitude as well as the πN∆ strong coupling constant. We show that the results are considerably improved in models that, in addition to the pion cloud, incorporate a fluctuating σ field inside the baryon.
Electromagnetic Nucleon-to-Delta Transition in Chiral Effective-Field Theory
Physical Review Letters, 2005
We perform a relativistic chiral effective-field theory calculation of the pion electroproduction off the nucleon ($e^- N \to e^- N \pi$) in the Delta(1232)-resonance region. After fixing the three low-energy constants, corresponding to the magnetic (M1), electric (E2), and Coulomb (C2) gammaNDelta\gamma N\Delta gammaNDelta couplings, our calculation provides a prediction for the momentum-transfer and pion-mass dependence of the gammaNDelta\gamma N\Delta gammaNDelta form factors. The prediction for the pion-mass dependence resolves the discrepancy between the recent lattice QCD results and the experimental value for the "C2/M1 ratio" at low Q2Q^2Q2.
Pion scattering and electro-production on nucleons in the resonance region in chiral quark models
2011
Pion scattering and electro-production amplitudes have been computed in a coupled-channel framework incorporating quasi-bound quark-model states, based on the Cloudy Bag model. All relevant low-lying nucleon resonances in the P33, P11, and S11 partial waves have been covered, including the Delta(1232), the N*(1440), N*(1535), and N*(1650). Consistent results have been obtained for elastic and inelastic scattering (two-pion, eta-N, and K-Lambda
Threshold pion photoproduction of nucleons in the chiral quark model
Physical review D: Particles and fields, 1994
In this paper, we show that the low energy theorem (LET) of the threshold pion-photoproduction can be fully recovered in the quark model. An essential result of this investigation is that the quark-pion operators are obtained from the effective chiral Lagrangian, and the low energy theorem does not require the constraints on the internal structures of the nucleon. The pseudoscalar quark-pion coupling generates an additional term at order µ = m π /M only in the isospin amplitude A (−). The role of the transitions between the nucleon and the resonance P 33 (1232) and P-wave baryons are also discussed, we find that the leading contributions to the isospin amplitudes at O(µ 2) are from the transition between the P-wave baryons and the nucleon and the charge radius of the nucleon. The leading contribution from the Pwave baryons only affects the neutral pion production, and improve the agreement with data significantly. The transition between the resonance P 33 (1232) and the nucleon only gives an order µ 3 corrections to A (−) .
Physical Review D, 2009
We examine the electromagnetic properties of the ∆(1232) resonance within the self-consistent chiral quark-soliton model. In particular we present the ∆ form factors of the vector-current GE0(Q 2 ), GE2(Q 2 ) and GM1(Q 2 ) for a momentum-transfer range of 0 ≤ Q 2 ≤ 1 GeV 2 . We apply the symmetry-conserving quantization of the soliton and take 1/Nc rotational corrections into account. Values for the magnetic moments of all decuplet baryons as well as for the N −∆ transition are given. Special interest is also given to the electric quadrupole moment of the ∆.