  We reanalyse the gamma-gamma scattering data and conclude that in the mass
region below 1 GeV the cross section for gamma-gamma to pi^0-pi^0 can be
largely explained by the one pion exchange process with pi-pi rescattering. The
radiative width of the sigma is estimated and a model dependent separation into
contributions from direct gamma-gamma decay and decay through rescattering is
obtained. We confront these findings with QCD spectral sum rule (QSSR)
predictions and conclude that the sigma can have a large gluonium component in
its wave function.
