“…In the region of small momenta one uses the condition µk ≪ 1 to simplify the integrand, and in the region of large momenta the same goal is achieved with the help of the condition k ≫ 1. Note that for k ≃ σ both conditions on the integration momenta are valid simultaneously, so in the sum of the low-momenta and high-momenta integrals all σ-dependent terms cancel and one obtains a σ-independent result for the total momentum integral (for a more detailed discussion of this method, see, e.g., [11]). All contributions, up to and including the corrections quadratic in the small mass ratio m/M, were analytically calculated earlier in this framework [6,10] (see also [11,5]).…”