A contribution to the discussion of the matter–antimatter asymmetry problem

Using a more accurate effective Hamiltonian governig the time evolution in the particle–antiparticle subspace of states than the one obtained within the Lee–Oehme–Yang approach we show that in the case of particles created at the instant t = t0 only the masses of a stable particle and its antiparticle are the same at all t ≥ t0 in a CPT invariant system, whereas the masses of an unstable particle and its antiparticle are equal only at t = t0 and then during their time evolution they become slightly different for times t ≫ t0 if CP symmetry is violated but CPT symmetry holds. This property is used to show that if the baryon number B is not conserved then the asymmetry between numbers of unstable baryons and antibaryons can arise in a CPT invariant system at t ≫ t0 even in the thermal equilibrium state of this system. e–mail: [email protected] , [email protected]