Light cone sum rules forγ*N→Δtransition form factors

Abstract

A theoretical framework is suggested for the calculation of N ! transition form factors using the light-cone sum rule approach. Leading-order sum rules are derived and compared with the existing experimental data. We find that the transition form factors in a several GeV region are dominated by the soft contributions that can be thought of as overlap integrals of the valence components of the hadron wave functions. The minus components of the quark fields contribute significantly to the result, which can be reinterpreted as large contributions of the quark orbital angular momentum.

Light-cone sum rules for theNγΔtransitions for real photons

“…[34,35] it has been shown that it is possible to disentangle the contribution to Π µν due to Eq. (44) and Eq.…”

“…However, it is known that the correlation function is plagued by transitions pγ → N * [34,35], where |N * is a isospin-3 2 spin-1 2 state with negative parity. It is advantageous to use the Lorentz structures that do not receive contributions due to transitions to spin-1 2 − states.…”

“…It is advantageous to use the Lorentz structures that do not receive contributions due to transitions to spin-1 2 − states. To find these we consider the overlap of |N * with η µ , which is defined [35] as…”

“…A comparison with this work is given in Section 3. As already stressed in previous works [34,35], it is important to choose the Lorentz basis in such a way that the unwanted contributions due to the non-vanishing overlap of states with spin 1/2 and negative parity with the ∆ interpolating field η µ can be separated from those of spin 3/2 states with positive parity.…”

“…[34,35], where nucleon-∆-transition form factors were calculated for virtual photons. In the both calculations that use different (local duality and LCSR, using nucleon distribution amplitudes [37]) techniques, the magnetic transition form factor comes out to be below the data for the momentum transfers below 2 GeV 2 , and the reason for this discrepancy is not understood.…”