Why do the mass of anti-particles have to be exactly equal to the particles ?
What I learnt from Srednicki Chapter 23 is that to support charge conjugation symmetry (C-symm) of Lagrangian, mass of particle and anti-particle must be same.
My question is "Is charge conjugation symmetry a universal truth -- proven by experiments, or we still can have some Lagrangians (L) which doesn't support C-symm., where changing + charged particles to - charged in L will not mean m+ = m- ?" What would existence of such a theory mean to our world ?