Electroweak baryogenesis

Electroweak baryogenesis is a proposed mechanism for producing the Universe’s excess of matter over antimatter during the electroweak phase transition, using baryon-number violation and CP violation.

Electroweak phase transition: The early-Universe transition associated with the breaking of electroweak symmetry as the Universe cooled. A strongly first-order transition would provide bubble walls and departures from equilibrium for baryogenesis.
Electroweak theory: The unified gauge theory of electromagnetic and weak interactions, based on the groups U(1) and SU(2). Its gauge fields and Higgs sector provide the interactions involved in the proposed transition.
Standard Model: The established quantum field theory describing known elementary particles and three of their fundamental interactions. Its CP violation and electroweak transition are generally insufficient to explain the observed asymmetry through this mechanism.
Gravitational waves from phase transitions: Gravitational waves produced by violent processes during cosmological first-order phase transitions. A sufficiently strong electroweak transition could leave a stochastic signal that tests some scenarios.
Electroweak baryon-number violation: Processes in the electroweak theory that violate baryon number through changes in gauge-field topology. These processes can convert a CP-asymmetric particle density near bubble walls into baryon number.
Higgs field: A field whose nonzero vacuum expectation value gives masses to elementary particles through their interactions with it. Its changing value across a bubble wall controls particle masses and electroweak symmetry breaking.
Leptogenesis: A class of mechanisms that generate a lepton asymmetry, later converted partly into baryon asymmetry by electroweak processes. It produces the primordial asymmetry through lepton-number physics rather than at the electroweak phase transition.
Electric dipole moment: A measure of the separation of positive and negative charge within a particle, forbidden for fundamental particles by some symmetries. New CP-violating sources can induce electric dipole moments constrained by precision experiments.
CP violation: A difference between the behavior of physical processes and their charge-conjugated, parity-reversed counterparts. It biases particle and antiparticle transport, a necessary ingredient for producing net baryon number.
Sphaleron: An unstable, finite-energy configuration of electroweak fields that mediates transitions between gauge vacua of different topology. Thermal sphaleron transitions provide the relevant baryon-number violation in the hot electroweak plasma.

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