Approximations used in calculating many-body effects in resonant [(dtμ)dee]*formation

The approximations needed to treat the resonant formation of the compound molecule [(dtμ)dee${]}^{\mathrm{*}}$ as a line-broadening process are examined. The necessary criteria for applying the impact (Lorentzian) approximation are shown to be seriously violated under the usual conditions of muon-catalyzed fusion. Neither the condition for binary collisions nor the requirement that the detuning not be too large holds. A much more appropriate description is the many-body quasistatic approximation, which is valid for large detunings at any density and for practically the whole profile at high densities. The convenient factorization of the three-body rate into a convolution of a two-body rate with a broadening factor is shown to hold within some approximations, but the broadening factor itself depends on the transition being considered.