Münster 2002 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 29: Theory IV

HK 29.2: Vortrag

Mittwoch, 13. März 2002, 14:30–14:45, A

Twist-3 generalized parton distributions from instantons — •Dmitri Kiptily¹ and M.V. Polyakov^1,2 — ¹Institute for Theoretical Physics II, Ruhr University Bochum, 44780 Bochum, Germany — ²Petersburg Nuclear Physics Institute, 188350 Gatchina, Russia

The Deeply Virtual Compton Scattering (DVCS) is a two photon scattering off a hadron considered in the Bjorken limit, when initial photon has a large virtuality. The leading twist contribution to the DVCS amplitude expresses through the Generalized Parton Distributions (GPD). The leading (twist-3) power corrections consist of two parts: the pure quark “kinematical” contribution expressed through twist-2 GPDs and the quark-gluon one originated from non-diagonal hadronic matrix elements of type ⟨ P′| q G q | P ⟩. The latter is supposed to be small relative to the “kinematical” one, although there wasn’t suggested any theoretical justification to this hypothesis.

We discuss the twist-3 quark-gluon effects in the DVCS. We estimate the non-diagonal hadronic matrix elements in a framework of the model of the instanton vacuum. It turns out, that the contribution is parametrically small due to the small packing fraction of the instanton vacuum.