Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

(From my homework) In our toy model we have three kinds of spinless particles: $A$, $B$, and $C$. The primitive vertex of decay/interaction is shown below: enter image description here

My actual problem statement says: "Suppose a diagram in our toy model for the Feynman Calculus has $N_A$ external $A$ lines, $N_B$ external $B$ lines, and $N_C$ external $C$ lines. Develop a simple rule for determining whether it is an allowed reaction."

If all the initial particles are $A$ then I was able to determine that $2N_A\geq N_B + N_C$ is a necessary restriction but I am not sure if this basic toy model restricts all initial particles to be $A$. Additionally, if the model restricts all final particles to be $B$ or $C$ then the inequality in my restriction becomes an equality. Does anyone have enough experience with this toy model to know if the only initial particles are $A$? If not, can you offer some suggestions to help me figure out an appropriate restriction for the general case, where $A$ $B$ and $C$ particles can all be initial or final particles?

EDIT: After talking with my professor he told me that the masses of each particle obey $m_A>m_B+m_C$, so that $A$ particles are able to decay into $B$ and $C$ but that reactions that produced $A$ particles as real (instead of virtual) particles are not allowed.

share|improve this question
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.