23 1 2 3 4 Q$^{2}$ [GeV$^{2}$] 10 0 10 1 10 2 10 3 σ$^{U}$  [nb] HERMES $_{U }$=  $_{T }$+ L L T 2 3 4 5 6 7 Q$^{2}$ [GeV$^{2}$] HERMES 4 5 6 7 8 9 10 11 Q$^{2}$ [GeV$^{2}$] HERMES 0.02 < x$_{B}$ < 0.15 0.15 < x$_{B}$ < 0.26 0.26 < x$_{B}$ < 0.55 FIG. 19: (Color online) Q 2 dependence of the integrated cross sections σ$_{U}$ = σ$_{T}$ + ϵσ$_{L}$ in exclusive reaction p ( γ $^{∗}$, π $^{+}$) n at HERMES. The different panels correspond to different x$_{B}$ bins. The solid curves are the model results. The dashed and dash-dotted curves correspond to the longitudinal ϵσ$_{L}$ and transverse σ$_{T}$ components of the cross section, respectively. The experimental data are from Ref. [7] tern of amplitudes where particles with opposite parities are exchanged. In the following we discuss briefly the generic features of the beam SSA in the present model. The compara- tive analysis of the SSA at JLAB and HERMES will be presented in the forthcoming publication. n al εσ$_{L}$ and the transverse σ$_{T}$ components, respectively. In the region of small Bjorken x$_{B}$ , see left panel in Fig- ure 19, the integrated longitudinal component dominates over the transverse cross section. With increasing x$_{B}$ the strength of the transverse component is increasing and for values of x$_{B}$ in the third bin the transverse cross sec- tion σ$_{T}$ becomes the dominant part of the exclusive cross section. An increase of the relative contribution of σ$_{T}$ as a function of x$_{B}$ can be clearly seen in the right panel of Figure 19 where 0 . 26 < x$_{B}$ < 0 . 55. There the first Q 2 bin corresponds to the average value of x$_{B}$ = 0 . 29 and the last Q 2 bin to the average value of x$_{B}$ = 0 . 44 [57]. In the left panel of Figure (20) we plot the CLAS data [6] for the azimuthal moment A sin( φ ) LU associated with the beam SSA, Eq. (8), in the reaction p ( ⃗ e, e ′ π $^{+}$) n . These data have been collected in hard scattering kinematics E$_{e}$ = 5 . 77 GeV, W > 2 GeV and Q 2 > 1 . 5 GeV $^{2}$. The experiment shows a sizable and positive beam SSA. In the left and right panels of Figure (20) we present the results for the azimuthal moments A sin( φ ) LU in the re- actions p ( ⃗ e, e ′ π $^{+}$) n and n ( ⃗ e, e ′ π − ) p , respectively. The ( Q $^{2}$, W ) binning of the experimental data point is not available. In the following the calculations are done for the lowest ( Q $^{2}$, W ) bin corresponding to the values of Q 2 = 1 . 5 GeV 2 and W 2 = 4 GeV $^{2}$. In this work we have restricted ourselves to exclusive ( e, e ′ π ± ) reactions with an unpolarized target. With a polarized beam ( ⃗ e, e ′ π ± ) and with an unpolarized target there is an additional component σ$_{LT}$ ′ , Eq. (3), which is proportional to the imaginary part of an interference between the l/t photons and therefore sensitive to the relative phases of amplitudes. At first, we consider A sin( φ ) LU generated by the ex- change of Regge trajectories. In Figure (20) the dashed curves describe the model results without the r/p -effects and neglecting the exchange of the axial-vector a$_{1}$ (1260) Regge trajectory. This model results in a zero A sin( φ ) LU and therefore a zero beam SSA. The addition of the un- natural parity a$_{1}$ (1260)-exchange generates by the inter- ference with the natural parity ρ (770) exchange a siz- able A sin( φ ) LU in both channels. This result corresponds to the dash-dotted curves in Figure (20). In the rest of observables discussed above the effect of the axial- In general, a nonzero σ$_{LT}$ ′ or the corresponding beam SSA A$_{LU}$ ( φ ), Eq. (7), demands interference between sin- gle helicity flip and nonflip or double helicity flip ampli- tudes. In Regge models the asymmetry may result from Regge cut corrections to single reggeon exchange [58]. This way the amplitudes in the product acquire different phases and therefore relative imaginary parts. A nonzero beam SSA can be also generated by the interference pat- XI. BEAM SPIN ASYMMETRY