[SOLVED] feynman rules Hi , It is a simple question from the book of david j .griffiths :"introduction to elementary particles" (6.11) 1. The problem statement, all variables and given/known data (a) Is A--->B+B a possible process in the ABC theory (feynman rules for a toy theory) (b)Suppose a diagram has nA external A lines , nB external B lines and nC external C lines. Develop a simple criterion for determining whether it is an allowed reaction . 2. Relevant equations 3. The attempt at a solution (a)I presume that if A is heavier than both B particles it should be a legitimate process . I am not sure whether there is any extra information needed for this question. (b)It is related to (a) , so I am certainly missing something .