In an interacting quantum field theory, for example, QED, the Dirac mass $m\bar{\psi}\psi$ is a piece of the free Dirac Lagrangian. On the other hand, the interaction term $j^\mu A_\mu=e\bar{\psi}\gamma^\mu\psi A_\mu$ is supposed to be solely responsible for creating or destroying a particle or an antiparticle.
However, the answer here by Lubos Motl states
"...the Dirac mass term destroys a particle and creates a new one, or destroys/creates a particle-antiparticle pair, or destroys an anti-particle and creates a new one."
In free theory, the particle number must be conserved. So my question is whether the interpretation of Lubos is valid.
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