e+e- → π+π-γ reaction at Q2=0.9-1.06 GeV2 and logarithmic singularity contribution of the triangle graph

The cross section of the e+e- → π+π-γ reaction at Q2=0.9-1.0 GeV2 is calculated with account of a contribution from an intermediate ωπ0 state containing a logarithmic singularity of the triangle graph. The observable effect owing to the singularity is proportional to the pion charge exchange amplitude, a±00=2/3(a2-a0) (where a0 and a2 are the ππ scattering lengths) near the threshold; if a0 ∼ ±(0.2-0.4)mπ-1 it amounts to 0.1-0.2 pbn, which makes the effect available to an experimental detection