> If I have a rho going to two pions, I can decompose the final > two-pion states into varoius linear combinations of the > eigenstates of total isospin, ie a|20> + b|10> + c|00> and suchlike. > > If your initial state is, for example, |10>, does this mean > that the final state *cannot* have |20> or |00> in it? Or does it > merely suggest that the final state must have at least > |10> in it? I realize that isospin must be conserved, but > the specifics are eluding me. It suggests that the final state *cannot* have I=2, 0 in it. Think about the angular momentum. If the initial state has J=1, your final state must also have *only* J=1, no other J. This is the same thing. Hitoshi