Explaining the origin of the slight excess of matter over antimatter in the universe remains one of the important, unsolved problems in particle physics, nuclear physics and cosmology. The so-called baryon asymmetry of the universe (BAU) is characterized by the ratio of the baryon number density to the photon entropy density, YB. We know from studies of the cosmic microwave background and big bang nucleosynthesis that YB is of order 10-10. Although this is a tiny number, it is hard to understand why YB differs from zero if the universe possessed equal amounts of matter and antimatter at its birth. Sakharov noted that if the universe began with symmetric initial conditions, then the particle physics interactions that took place as the universe evolved would have to contain three ingredients: (1) baryon number violation, (2) violation of C- and CP-symmetry, and (3) a departure from thermal equilibrium (the last criterion can be evaded if CPT symmetry is violated). University of Wisconsin-More to digest!
Posted on: Fri, 19 Jul 2013 12:51:35 +0000
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