  We present a numerical solution of the four-quark Bethe-Salpeter equation for
a scalar tetraquark. We find that the four-body equation dynamically generates
pseudoscalar poles in the Bethe-Salpeter amplitude. The sensitivity to the pion
poles leads to a light isoscalar tetraquark mass M ~ 400 MeV, which is
comparable to that of the sigma/f0(500). The masses of its multiplet partners
kappa and a0/f0 follow a similar pattern, thereby providing support for the
tetraquark interpretation of the light scalar nonet.
