Baryon asymmetry

Neither the standard model of particle physics nor the theory of general relativity provides a known explanation for why this should be so, and it is a natural assumption that the universe is neutral with all conserved charges.

[4] In 1967, Andrei Sakharov proposed[5] a set of three necessary conditions that a baryon-generating interaction must satisfy to produce matter and antimatter at different rates.

These conditions were inspired by the recent discoveries of the Cosmic microwave background[6] and CP violation in the neutral kaon system.

Finally, the interactions must be out of thermal equilibrium, since otherwise CPT symmetry would assure compensation between processes increasing and decreasing the baryon number.

Mathematically, the commutator of the baryon number quantum operator with the (perturbative) Standard Model hamiltonian is zero:

The second condition for generating baryon asymmetry—violation of charge-parity symmetry—is that a process is able to happen at a different rate to its antimatter counterpart.

In the Standard Model, CP violation appears as a complex phase in the quark mixing matrix of the weak interaction.

That way finding a non zero electric dipole moment would imply the existence of T-violating interactions in the vacuum corrections to the measured particle.

In this situation the particles and their corresponding antiparticles do not achieve thermal equilibrium due to rapid expansion decreasing the occurrence of pair-annihilation.

Another possible explanation of the apparent baryon asymmetry is that matter and antimatter are essentially separated into different, widely distant regions of the universe.

[4] The state of the universe, as it is, does not violate the CPT symmetry, because the Big Bang could be considered as a double sided event, both classically and quantum mechanically, consisting of a universe-antiuniverse pair.

This model, devised by physicists from the Perimeter Institute for Theoretical Physics in Canada, proposes that temperature fluctuations in the cosmic microwave background (CMB) are due to the quantum-mechanical nature of space-time near the Big Bang singularity.

[14] This model has not shown if it can reproduce certain observations regarding the inflation scenario, such as explaining the uniformity of the cosmos on large scales.

According to the Big Bang model, matter decoupled from the cosmic background radiation (CBR) at a temperature of roughly 3000 kelvin, corresponding to an average kinetic energy of 3000 K / (10.08×103 K/eV) = 0.3 eV.