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When people are being careful they'll tell you that antiparticles are the CPT conjugates of particles. You can't say that they are C conjugates or CP because these, while they do reverse the charge, are not symmetries of the Hamiltonian and so are not physical (anti)particles.

However, in leptogenesis, one explicitly calculates the CP asymmetry as a measure of the matter-antimatter asymmetry. Since CP violation is part of the theory, then the CP conjugates of physical particles are not physical antiparticles. This means that the resulting asymmetry is not literally the baryon asymmetry of the universe.

Why is this legitimate? Perhaps it's because CP violation is very slight and appears in the decays which destroy the leptons we are counting. Therefore if we imagine them to have long enough lifetimes to be countable real particles, then they are also essentially CP eigenstates?

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