Electroweak structure of the nucleon, meson cloud, and light-cone wave functions

Pasquini, B.; Boffi, S.

doi:10.1103/physrevd.76.074011

Cited by 56 publications

(53 citation statements)

References 84 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The axial form factors of the octet baryons, including the nucleon, have been studied using constituent and chiral quark models [13,[25][26][27][28][29][30][31][32][33][34][35][36][37], based on the DysonSchwinger equations [38][39][40][41], models with meson cloud dressing [42][43][44][45][46][47][48][49][50][51][52][53][54], large-N C and chiral perturbation theory [5,[55][56][57][58][59][60][61][62][63][64][65] and QCD sum rules [66][67][68]. Recently, lattice QCD simulations for the nucleon became available for Q 2 = 0 [69][70][71]…”

Section: Introductionmentioning

confidence: 99%

Axial form factors of the octet baryons in a covariant quark model

Ramalho

Tsushima

2016

Phys. Rev. D

View full text Add to dashboard Cite

We study the weak interaction axial form factors of the octet baryons, within the covariant spectator quark model, focusing on the dependence of four-momentum transfer squared, Q 2 . In our model the axial form factors GA(Q 2 ) (axial-vector form factor) and GP (Q 2 ) (induced pseudoscalar form factor), are calculated based on the constituent quark axial form factors and the octet baryon wave functions. The quark axial current is parametrized by the two constituent quark form factors, the axial-vector form factor g q A (Q 2 ), and the induced pseudoscalar form factor g q P (Q 2 ). The baryon wave functions are composed of a dominant S-state and a P -state mixture for the relative angular momentum of the quarks. First, we study in detail the nucleon case. We assume that the quark axial-vector form factor g q A (Q 2 ) has the same function form as that of the quark electromagnetic isovector form factor. The remaining parameters of the model, the P -state mixture and the Q 2 -dependence of g q P (Q 2 ), are determined by a fit to the nucleon axial form factor data obtained by lattice QCD simulations with large pion masses. In this lattice QCD regime the meson cloud effects are small, and the physics associated with the valence quarks can be better calibrated. Once the valence quark model is calibrated, we extend the model to the physical regime, and use the low Q 2 experimental data to estimate the meson cloud contributions for GA(Q 2 ) and GP (Q 2 ). Using the calibrated quark axial form factors, and the generalization of the nucleon wave function for the other octet baryon members, we make predictions for all the possible weak interaction axial form factors GA(Q 2 ) and GP (Q 2 ) of the octet baryons. The results are compared with the corresponding experimental data for GA(0), and with the estimates of baryon-meson models based on SU (6) symmetry.

show abstract

Section: Introductionmentioning

confidence: 99%

Axial form factors of the octet baryons in a covariant quark model

Ramalho

Tsushima

2016

Phys. Rev. D

View full text Add to dashboard Cite

show abstract

“…in rough agreement with our results. Figure 2 shows several model calculations and fits for the form factor ratio [21,23,24,25,26,27,28,29,30,31,32,33], which are seen to vary greatly. Improved experiments [8] would be able to distinguish these diverse approaches, and more fundamentally, better determine the value of (R * 2 M − R * 2 E ).…”

mentioning

confidence: 99%

Proton Electromagnetic-Form-Factor Ratios at LowQ2

2008

View full text Add to dashboard Cite

We study the ratio R ≡ µG E (Q 2 )/G M (Q 2 ) of the proton at very small values of Q 2 . Radii commonly associated with these form factors are not moments of charge or magnetization densities. We show that the form factor F 2 is correctly interpretable as the two-dimensional Fourier transformation of a magnetization density. A relationship between the measurable ratio and moments of true charge and magnetization densities is derived. We find that existing measurements show that the magnetization density extends further than the charge density, in contrast with expectations based on the measured reduction of R as Q 2 increases.PACS numbers: 13.40.-f,13.40.Em,13.40.Gp,13.60.-r,14.20.Dh Keywords: form factors, charge densities Electromagnetic form factors of the proton and neutron (nucleon) are probability amplitudes that the nucleon can absorb a given amount of momentum and remain in the ground state, and therefore should determine the nucleon charge and magnetization densities. Much experimental technique, effort and ingenuity has been used recently to measure these quantities [1,2].The text-book interpretation of electromagnetic form factors, G E , G M , explained in [2], is that their Fourier transforms are measurements of charge and magnetization densities, and conventional wisdom relates the charge and magnetization mean square radii to the slopes of G E,M at Q 2 = 0. However, this interpretation is not correct because the wave functions of the initial and final nucleons have different momenta and therefore differ, invalidating a probability or density interpretation. A proper charge density is related to the matrix element of an absolute square of a field operator.Here we show that the proper magnetization density is the two-dimensional Fourier transform of the F 2 form factor. We use this and the result that the charge density is the two-dimensional Fourier transform of the F 1 form factor [3,4,5,6] to show that the magnetization density of the proton extends significantly further than its charge density. This is surprising because the observed rapid decrease of the ratio of electric to magnetic form factors with increasing values of Q 2 [1, 2] might lead one to conclude that the charge radius is larger than the magnetization radius.Form factors are matrix elements of the electromagnetic current operator J µ (x ν ) in units of the proton charge:

show abstract

“…Such calculations exist in the literature (see, e.g., Ref. [4]), but in all the work known to us the strong pion-baryon vertices were parameterized. We rather try to treat strong and electromagnetic vertices on the same footing, i.e.…”

Section: Resultsmentioning

confidence: 99%

On the Microscopic Structure of $${\varvec{\pi }}$$ π NN, $${\varvec{\pi }}$$ π N $${\varvec{\Delta }}$$ Δ and $${\varvec{{\pi }\Delta \Delta }}$$ π Δ Δ Vertices

Jung

Schweiger

2017

Few-Body Syst

View full text Add to dashboard Cite

We use a hybrid constituent-quark model for the microscopic description of π N N, π N and π vertices. In this model quarks are confined by an instantaneous potential and are allowed to emit and absorb a pion, which is also treated as dynamical degree of freedom. The point form of relativistic quantum mechanics is employed to achieve a relativistically invariant description of this system. Starting with an SU (6) spin-flavor symmetric wave function for N 0 and 0 , i.e. the eigenstates of the pure confinement problem, we calculate the strength of the π N 0 N 0 , π N 0 0 and π 0 0 couplings and the corresponding vertex form factors. Interestingly the ratios of the resulting couplings resemble strongly those needed in purely hadronic coupled-channel models, but deviate significantly from the ratios following from SU(6) spin-flavor symmetry in the non-relativistic constituent-quark model. Motivation and FormalismOur interest in π N N, π N and π couplings and vertex form factors is connected with our attempt to take pion-loop effects into account when describing the electromagnetic structure of N and within a constituentquark model. As it turns out, the calculation of the loop effects boils down to a purely hadronic problem, in which the quark substructure of the N and the is hidden in strong and electromagnetic form factors of "bare" baryons, i.e. eigenstates of the pure confinement problem. Since π N N, π N and π couplings and vertex form factors are basic building blocks of nuclear physics and every hadronic model of meson-baryon dynamics, their microscopic description is also highly desirable on more fundamental grounds.Our starting point for calculating the strong π N N, π N and π couplings and form factors is the mass-eigenvalue problem for three quarks that are confined by an instantaneous potential and can emit and reabsorb a pion. To describe this system in a relativistically invariant way, we make use of the point-form of relativistic quantum mechanics. Employing the Bakamjian-Thomas construction, the overall four-momentum operatorP μ can be separated into a free 4-velocity operatorV μ and an invariant mass operatorM that contains all the internal motion, i.e.P μ =MV μ [1]. Bakamjian-Thomas-type mass operators are most conveniently represented by means of velocity states |V ; k 1 , μ 1 ; k 2 , μ 2 ; . . . ; k n , μ n , which specify an n-body system by its overall velocity V (V μ V μ = 1), the CM momenta k i of the individual particles and their (canonical) spin projections μ i [1]. Since the physical baryons of our model contain, in addition to the 3q-component, also a

show abstract

Electroweak structure of the nucleon, meson cloud, and light-cone wave functions

Cited by 56 publications

References 84 publications

Axial form factors of the octet baryons in a covariant quark model

Axial form factors of the octet baryons in a covariant quark model

Proton Electromagnetic-Form-Factor Ratios at LowQ2

On the Microscopic Structure of $${\varvec{\pi }}$$ π NN, $${\varvec{\pi }}$$ π N $${\varvec{\Delta }}$$ Δ and $${\varvec{{\pi }\Delta \Delta }}$$ π Δ Δ Vertices

Contact Info

Product

Resources

About