How have antiparticles disappeared in the universe?

How the decay of particles overtook that of antiparticles…

It is observed that the number of baryons in the universe (protons and neutrons) exceeds the number of antibaryons at least ten thousand times. Such an asymmetry could arise in the early universe where there were some particles whose decays led to an increase of the number of baryons. Furthermore, the decay of these particles had to go more intensively than the decay of the corresponding antiparticles. Otherwise, the latter would reduce the number of baryons and compensate for their increase originated from the former process. Expansion of the universe carried the products of decay away from each other so rapidly that the reverse reaction of their synthesis did not manage to restore an equal number of baryons and antibaryons.

Annihilation under the baryon asymmetry

Because of the fast expansion of space, the decay products could hardly meet again for synthesis.

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