We seek to explore the origin of the matter-antimatter asymmetry in the Universe. We study quantitatively the conditions in which matter (protons, neutrons) formed in the Early Universe during a period which spanned 10-50mus. We obtain all chemical potentials implied by the present day baryon-to-photon ratio. In the mixed hadron-quark phase, a significant hadron sector electric charge distillation is found.

The question as to why the Universe is made of matter is one of the great unsolved mysteries of physics. In the standard big-bang model, the large primordial baryon and antibaryon abundance formed at hadronization of the deconfined quark-gluon plasma (QGP) disappears due to mutual annihilation, exposing a slight net baryon number observed today. Applying the knowledge of equations of state of hadronic matter derived from the study of high energy nuclear collisions we consider quantitatively this evolution epoch of the early Universe.

The annihilation period began after the phase transformation from the QGP to a hot hadronic gas (HG), when the Universe was at a temperature of about 170eV, and continued until the density had diminished to the level that a ``nucleon freeze-out'' occurred at approximately 1ms, when T = 35MeV. In this scenario, annihilation of antimatter was very complete, quantified by the result that the energy fraction in baryons and antibaryons in the Universe dropped from 10%when Universe was about 40mus old to 10{-7} when it was one second old.

The observational evidence about the antimatter non-abundance in the Universe is supported by the highly homogeneous cosmic microwave background derived from the period of photon decoupling. This has been used to argue that the matter-antimatter domains on a scale smaller than the observable Universe are unlikely; others see need for further experimental study to confirm this result.

The current small value of the baryon-to-photon ratio is the result of this near complete annihilation of the large matter-antimatter abundance. Other than a (relatively) small increase in photons during nucleosynthesis and electron-ion recombination, eta, the baryon and photon numbers should be preserved back to the period of annihilation. Considering several observables, a range of eta is established, the latest WMAP result is eta = n_B/n_gamma = 6.1^{+0.3}_{-0.2} 10{-10}.

The importance of eta is that it allows to determine the value of entropy per baryon S/B in the Universe, which is conserved in adiabatic evolution. At present the entropy is dominated by photons, and nearly massless (decoupled) neutrinos. It is straightforward to compute the entropy densities of these species from the partition function, and then to convert \eta to S/B using the photon number density. We obtain a value of S/B = 8.0/eta=1.3 \pm 0.1 10^{10}, assuming a lower neutrino than photon temperature (photons are reheated by e^+e^-annihilation), and counting only left/right-handed neutrinos/antineutrinos.

Further research details are available in Hadronization of the Quark Universe by Michael J. Fromerth, and Johann Rafelski

The limit on asymmetry between particle and antiparticle masses is discussed in Limit on Quark-Antiquark Mass Difference from the Neutral Kaon System by Michael J. Fromerth, and Johann Rafelski