Revisiting γγ→π+π− at low energies

We complete the recalculation of the available two-loop expressions for the reaction γγ→ππ in the framework of chiral perturbation theory. Here, we present the results for charged pions. The cross section and the values of the dipole polarizabilities agree very well with the earlier calculation, provided the same set of low-energy constants (LECs) is used. With updated values for the LECs at order p4, we find for the dipole polarizabilities (α1−β1)π±=(5.7±1.0)×10−4fm3, which is in conflict with the experimental result recently reported by the A2 Collaboration at MAMI.