Dy. Ivanov et L. Szymanowski, On the Coulomb corrections to the total cross section of the interaction of the pi(+)pi(-) atom with ordinary atoms at high energy, EUR PHY J A, 5(1), 1999, pp. 117-121
The size of pi(+)pi(-) atom in the low lying states is considerably smaller
than the radius of atomic screening. Due to that we can neglect this scree
ning calculating the contribution of multi-photon exchanges. We obtain the
analytic formula for Coulomb corrections which works with a very good accur
acy for the ground state of pi(+)pi(-) atom.