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- Thread starter lefebvre
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- #2

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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?

- #3

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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: [tex]H_{I}=g\phi\bar{\psi}\psi+h.c.[/tex]

And I have to use it to fermion decay. Isn't this the simplest Yukawa theory? Does this hermitian conjugate make different?

- #4

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OK, I can see that the hamiltonian is: [tex]H_{I}=g\phi\bar{\psi}\psi+h.c.[/tex]

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.

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