Lets see the reaction:

$e^- \mu^- \to e^- \pi^- \nu_\mu \;\;\;\;\;\;\;\;\;\;\; {(1)}$

I suppose, that this reaction occurs as follows

$e^- \mu^- \to e^- \mu^- \pi^+ \pi^- \to e^- \pi^- \nu_\mu$

Is it possible at energy less than 2*140 MeV?

The same is for the analogous proton-muon reaction

$p^+ \mu^+ \to p^+ \pi^+ \bar{\nu}_\mu \;\;\;\;\;\;\;\;\;\;\;{(2)}$

Once more reaction:

$p^+ p^+ \to p^+ p^+ \pi^- \pi^+ \to p^+ n \pi^+ \;\;\;\;\;\;\;\;\;\;\;{(3)}$

What are the experimental data?

P.S. This question is important enough. The main solar reaction is

$p^+ p^+ \to d^+ e^+ \nu_e $

If this reaction occurs as follows

$p^+ p^+ \to p^+ p^+ e^- e^+ \to p^+ n \nu_e e^+ \to d^+ e^+ \nu_e$

then it would require the energy of more than 2*0.511 MeV to take place. Cross section of this reaction will be much less, so the main solar reaction should be

$p^+ p^+ e^- \to d^+ \nu_e $

Edited 20.02.11

Why I think so? I suppose that new particles are created in pairs particle-antiparticle. So the reaction

$e^- e^- \to e^- e^- \pi^- \pi^+ $

requires the energy of more than 2*140 MeV to take place

As well as the reaction

$e^- e^- \to e^- e^- \pi^- e^+ \nu_e \to e^- \pi^- \nu_e $

from symmetry considerations, since there is a decay

$\pi^+ \to e^+ \nu_e$

And the result is

$e^- e^- \to e^- e^- \pi^- e^+ \nu_e \to e^- \pi^- \nu_e $

contrary to

$e^- e^- \to e^- \nu_e W^- \to e^- \pi^- \nu_e$

with the minimum reaction energy of 140 MeV

The same is valid for the reactions (1) (2) (3)

So what is the experimental data on minimum energy of these reactions?