NLO twist-3 contribution to the pion electromagnetic form factors in kT factorization

In this paper, by employing the k(T) factorization theorem, we calculate first the next-to-leading-order (NLO) twist-3 contributions to the pion electromagnetic form factors in the pi gamma(*)->pi process. From the analytical and numerical calculations we find the following points: (a) for the leading-order (LO) twist-2, twist-3, and the NLO twist-2 contributions, our results agree very well with those obtained in previous works, (b) we extract out two factors F-T3((1))(x(i), t, Q(2)) and (F) over bar ((1))(T3) (x(i), t, Q(2)), which describe directly the NLO twist-3 contributions to the pion electromagnetic form factors F+(Q(2)), (c) the NLO twist-3 contribution is negative in sign and cancels partially with the NLO twist-2 part, so the total NLO contribution can therefore provide a roughly +/-20% corrections to the total LO contribution in the considered ranges of Q(2), and (d) the theoretical predictions for Q(2)F(+)(Q(2)) in the low-Q(2) region agree well with currently available data, which can be improved by the inclusion of the NLO contributions.