  Two pion effective mass and helicity angle distributions in the charged
B-meson decays into three charged pions are studied. The weak decay amplitudes
are calculated in the framework of the QCD factorization approximation. The
strong interactions between the pairs of pions are taken into account using
scalar and vector pion form factors. The scalar form factors are constrained by
data on pion-pion, kaon-antikaon and four pion production incorporated into a
multichannel model of the coupled amplitudes. The vector form factor is
obtained from the Belle Collaboration analysis of the tau- --> pi- pi0 nu_{tau}
decays. The theoretical distributions of the dipion effective masses are
compared with the corresponding results of the recent Dalitz plot analysis of
B+- --> pi+pi-pi+- decays performed by the BABAR Collaboration. We find that
the S-wave dipion amplitude, although much smaller than the P-wave amplitude,
plays an important role even in the rho(770) mass range. We show that the
helicity angle distribution is strongly asymmetric in the rho- meson range.
This effect can be attributed to the broad f0(600)(or sigma) meson. The fact
that the signal of the B+- --> f0(980) pi+- decay has not been found in the
experimental analysis can be easily explained in our model since the relevant B
decay amplitude is proportional to the scalar form factor which has a dip at
the f0(980) mass. We obtain a unified unitary description of the contribution
of the three scalar resonances f0(600), f0(980) and f0(1400) in terms of the
pion non-strange scalar form factor.
