Baryon Asymmetry in the Universe and Neutrinos

Abstract

The number of baryons in the universe is of an order of magnitude just enough to form galaxies. Human beings would not have existed if there were too many or too few, say, beyond two orders of magnitude either way. In the modern view, the origin of baryons in the universe is ascribed to the action of baryon number (B) violating elementary processes in some early epoch of the universe, rather than is given as an initial condition. Sakharov pointed out that universe’s baryon asymmetry may be explained if three conditions cooperate: (i) there is a fundamental process that violates baryon number, (ii) C and CP invariance is violated at the same time, and (iii) there is a deviation from thermal equilibrium acting on the B violating process [1547].