content_image/436057.jpg
<img src='content_image/436057.jpg'>

jectory. However, in electroproduction the π − /π + asym- metry is driven by the resonance contributions through the different ( Q $^{2}$, s ( u )) dependence of the transition form factors, Eqs. (43) and (44), in the π + and π − channels. For instance, the dash-dotted curves in Figure 11 do not account for the contributions of resonances; the π − /π + ratio is bigger than unity. In the right panel we show the results for the values of Q 2 = 1 . 35 GeV 2 and ε = 0 . 84. 

Our dash-dotted curves which describe the Regge model without the r/p -effects are at variance with the results reported in Ref. [53] where the gauge invariant Regge model with the nucleon-pole contribution has been 

shown to be in remarkable agreement with t he π − /π + electroproduction ratio. This is surprising since the model of [53] is not compatible with the JLAB l/t data in the same ( Q $^{2}$, W ) region [4]. 

Before drawing definite conclusions concerning these discrepancies, we compare in Figure 12 our model results with the measured differential cross sections dσ$_{U}$/dt = dσ$_{T}$/dt + εdσ$_{T}$/dt (top), dσ$_{TT}$/dt (middle) and dσ$_{LT}$/dt (bottom) in exclusive reactions p ( γ ∗ , π $^{+}$) n (left panels) and n ( γ ∗ , π − ) p (right panels). The experimental data are from Refs. [13, 14]. The average values of ( Q $^{2}$, W, ε ) are the same as in Figure 11 for the π − /π + ratio. The 

