The influence of strong interaction on the pionium wave functions at small distances

The influence of the strong π+π−-interaction of the behaviour of pionium nS-state wave functions at small distances is studied both analytically (perturbatively) and numerically. It is shown that on the whole the accounting of strong interaction results in multiplying pure Coulomb pionium wave functions by some function which is practically independent of the value of the principal quantum number n. Due to this reason, the n-dependence of π+π−-atom production probability in nS-state remains the same as in the case of the pure Coulomb π+π−-interaction.