Modified perturbation theory for pair production and decay of fundamental unstable particles

Understand

We construct an asymptotic expansion in powers of the coupling constant directly of the cross-section for pair production and decay of fundamental unstable particles.

• The resonant and kinematic singularities arising in the expansion we treat in the sense of distributions.
• This mode allows us to transform formally divergent integrals into absolutely convergent ones with keeping the asymptotic property of the expansion.
• The appropriate procedure is elaborated up to an arbitrary order of the expansion.