Baryogenesis

The baryogenesis is the theory for dynamic creation (Greek genesis ) of the baryon asymmetry, namely the imbalance of matter ( baryons ) and antimatter ( antibaryons ) in the universe. On the baryogenesis the far better understood primordial nucleosynthesis followed.

Question

Our visible universe is made mostly of matter and only a small fraction of antimatter. Both kinds of matter are annihilated when meeting with energy release in a so-called annihilation reaction.

• On the one hand there is the possibility to assume that this asymmetry is a (random) initial condition of the universe.
• On the other hand, it would be obvious to assume that matter and antimatter were present at the beginning of the universe in equal amounts and the asymmetry only dynamically created during the evolution of the universe to the present time. Theoretical models that accomplish this are grouped under the term baryogenesis.

Sakharov's conditions for the baryon asymmetry

Andrei Sakharov recognized in 1967 as first the conditions that are necessary for the occurrence of asymmetry. Regardless of him, the Russian researcher Vadim Kuzmin found 1970 these conditions.

Sakharov's work was not known for a long time in the West. Even before it became known published Leonard Susskind own theories of baryogenesis.

The various theories differ in the way how these conditions in detail theoretically be met.

Non-conservation of baryon number

The baryon number may not be constant but must be in the course of the Big Bang change.

Fulfillment: in the GUT (Grand Unified Theory ), there are two ways in which a heavy X boson could decay. However, both decay chains occur with different probabilities, which changes the baryon number:

= 0.51 × ( 2 / 3 ) 0.49 × (-1 / 3) = 0.177

The antiparticle of the X - boson decays, however, as follows:

= 0.49 × (-2 / 3) 0.51 × ( 1 / 3) = -0.157

This violation of the baryon number can be explained by the so-called sphaleron interaction between quarks and leptons.

Symmetry breaking

Two symmetries between particles and antiparticles must be broken.

Performance: currently only very weak CP violations are known, which can not explain the presence of the baryon asymmetry. The CP- symmetry (C for engl batch charge;. P for parity Parity ) describes a course in which a particle is transformed into an antiparticle (or vice versa ), and parity ( spatial orientation ) changes. If you can not reverse this course unique, so it is called a symmetry breaking.

Thermal imbalance

There must be a loss of thermal equilibrium.

Fulfillment: the universe cools through its expansion. This can no longer run all reactions with equal probability, and two quarks no longer have the energy necessary to produce an X - boson.

Leptogenesis

Recent theories on the development of the baryon asymmetry favoring the leptogenesis. Here the asymmetry is first generated between leptons and antileptons and then converted by so-called sphaleron processes in the baryon asymmetry.