# Feynman rules for Yukawa theory

Hi. Do you know any book/paper/lecture notes where I can find complete derivation of Feynman rules for both scalar and pseudo-scalar Yukawa theory, and maybe an example of application to decay of fermion?

Srednicki's QFT book does pseudoscalar Yukawa theory.

maybe an example of application to decay of fermion?

The fermion won't decay in a Yukawa theory because the fermion number is conserved. Unless you have something more than the simplest theory in mind?

The fermion won't decay in a Yukawa theory because the fermion number is conserved. Unless you have something more than the simplest theory in mind?

OK, I can see that the hamiltonian is: $$H_{I}=g\phi\bar{\psi}\psi+h.c.$$
And I have to use it to fermion decay. Isn't this the simplest Yukawa theory? Does this hermitian conjugate make different?

OK, I can see that the hamiltonian is: $$H_{I}=g\phi\bar{\psi}\psi+h.c.$$
And I have to use it to fermion decay. Isn't this the simplest Yukawa theory? Does this hermitian conjugate make different?

Are you talking about decay of the ##\psi## particle? There is a U(1) symmetry ##\psi \to e^{i \theta} \psi## under which the Hamiltonian is invariant. This leads to conservation of ##\psi## number. So the ##\psi## particle can't decay. Said another way, in this theory there are no Feynman diagrams you can draw that represent the decay of a ##\psi## particle.