Structure of the neutral pion and its electromagnetic transition form factor

Abstract

The γ * γ → π 0 transition form factor, G(Q 2 ), is computed on the entire domain of spacelike momenta using a continuum approach to the two valence-body bound-state problem in relativistic quantum field theory: the result agrees with data obtained by the CELLO, CLEO and Belle Collaborations. The analysis unifies this prediction with that of the pion's valence-quark parton distribution amplitude (PDA) and elastic electromagnetic form factor, and demonstrates, too, that a fully self-consistent treatment can readily connect a pion PDA that is a broad, concave function at the hadronic scale with the perturbative QCD prediction for the transition form factor in the hard photon limit. The normalisation of that limit is set by the scale of dynamical chiral symmetry breaking, which is a crucial feature of the Standard Model. Understanding of the latter will thus remain incomplete until definitive transition form factor data is available on Q 2 > 10 GeV 2 .

Chimera distribution amplitudes for the pion and the longitudinally polarized ρ -meson

“…On the other hand, DAs with downward concave shapes in the entire interval x ∈ [0, 1], will tend to overestimate most data of the Belle Collaboration [47], the reason being that they give rise to large inverse-moment values (Table I) and [4,5] (see also [64]). [The opposite behavior was found in [66], as already mentioned. ]…”

“…18 there). But notice that a subsequent DSE-based computation [66] of the TFF, in which the role of the inverse moment is not so crucial, finds good agreement with the CELLO, CLEO, and Belle data in the entire domain of spacelike momenta.…”

Quark-gluon vertex: A perturbation theory primer and beyond

“…The associated corrections cancel for the pseudoscalar and vector mesons but add in the scalar and axial vector channels, [46], hence solving a long standing puzzle. On the other hand, the choice of the quark-gluon vertex (and quark-photon vertex, as the hadrons are probed through photons) is also critically important in studying the form factors of mesons, [47,48], and baryons, [49].…”

Aspects of open-flavour mesons in a comprehensive DSBSE study

“…From the theory point of view, one needs a thorough understanding of nonperturbative QCD, which is sought via different approaches such as the traditional quark model in relativistic forms [3][4][5][6][7][8][9][10][11], effective field theories [12][13][14][15], QCD sum rules (QSRs) [16][17][18][19], latticeregularized QCD [20][21][22][23][24], and covariant approaches to QCD bound states at various levels of sophistication and aspects pertaining thereto [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41].…”