Sphaleron

The sphaleron (Greek "ready to fall") is a hypothetical excitation of the vacuum in the standard model of elementary particle physics , which plays a role in some theories of baryogenesis .

The Sphaleron processes were first described mathematically in 1984 by Frans Klinkhamer and Nicholas Manton . They cannot be described in terms of perturbation theory within the framework of the quantum field theory of the Standard Model. They have not yet been confirmed experimentally.

The vacuum states of the electroweak theory are ambiguous in the Standard Model, and so the potential has a periodic structure of minima. If a system changes from one vacuum state to the other, this is done by means of so-called sphalerons. These are unstable solutions to the field equations that exist between the vacuums. Sphalerons take their way across the potential barrier between the vacuums (at energies of E  > 100 GeV).

There is also the possibility of tunneling from one vacuum to the next , this process is known as instanton . However, since tunnel effects are exponentially suppressed, such processes are very unlikely.

Clearly speaking, the sphalerons serve as a valve between leptons and baryons , since they can transfer one type of particle into the other. Three quarks (one of each color charge ) from each of the three particle families take part in a Sphaleron process , as well as one lepton each from the corresponding lepton family. All must be right handed .

Sphalerons receive the difference between the baryon number and the lepton number ${\displaystyle B}$ ${\displaystyle L}$ , but violate their sum . This means that baryogenesis via leptogenesis can also take place using sphalerons . ${\displaystyle B-L}$ ${\displaystyle B+L}$

literature

• Cline, James M .: The Origin of Matter. In: Spectrum of Science. November, 2004.
• Mark Trodden: Baryogenesis and Leptogenesis , 12/2004, arxiv : hep-ph / 0411301