Electroweak Baryogenesis

A class of mechanisms for generating the matter-antimatter asymmetry during the electroweak phase transition in the early universe, when the electromagnetic and weak forces took on their distinct identities. This scenario is attractive because it occurs at an energy scale (~100 GeV) potentially accessible to particle colliders like the LHC. It requires the phase transition to be strongly first-order to provide the necessary departure from thermal equilibrium (Sakharov's 3rd criterion), creating expanding bubbles of the new phase where CP-violating interactions (2nd criterion) at the bubble walls can generate a baryon asymmetry. The mechanism also relies on sphalerons - non-perturbative field configurations that violate baryon number (1st criterion) - to be active outside the bubbles but suppressed inside to preserve the created asymmetry. Its testability is a major motivation, but it requires physics beyond the Standard Model to provide a sufficiently strong first-order phase transition and new sources of CP violation.

The baryon surplus might have come about during a phase transition soon after the birth of the cosmos called electroweak symmetry breaking (EWSB), but only if EWSB was a first-order transition, akin to evaporating water. Bubbles of energy in a field permeating all of space, called the Higgs field, were needed to create two environments: the space outside the bubbles where antileptons could morph into baryons via quantum tunneling events called sphaleron processes, and the space inside the bubbles where they couldn't. The mass of the Higgs boson suggests that the temperature of EWSB was too low for a first-order transition.
However, if additional Higgs-like particles are found at higher energies, this theory becomes viable.