Baryogenesis

Abstract

Observations show that, at least in our astronomical neighborhood, the Universe is matter-dominated. The amount of antimatter is very small and it can be explained by its secondary production in high energy cosmic ray collisions or in catastrophic astrophysical phenomena. While there are many potentially possible scenarios proposed in the literature for the creation of the observed matter-antimatter asymmetry, we do not yet know the exact mechanism responsible for it. An initially tiny asymmetry seems to be excluded by the inflationary paradigm and therefore it is necessary a baryogenesis period, namely the creation of an asymmetry between baryons and antibaryons. Today we know that the Standard Model of particle physics cannot do it, and therefore the observed matter-antimatter asymmetry can be seen as an evidence of new physics. Baryogenesis models usually involve very high energy physics, which makes these scenarios extremely difficult to test with the available accelerator energies.

Problems

7.1

How can the charge asymmetry generated in heavy particle decays vanish in equilibrium? It is stated in the literature that the inverse decay does the job. However, one can see that it is not so because, using CPT, one finds:

$$\begin{aligned} \varGamma _{\bar{q} \bar{q} \rightarrow \bar{X} } = (1+\varDelta _q)\varGamma _q \, , \quad \varGamma _{ q l \rightarrow \bar{X} } = (1-\varDelta _l)\varGamma _l \, , \nonumber \\ \varGamma _{ q q \rightarrow X } = (1-\varDelta _q)\varGamma _q \, , \quad \varGamma _{ \bar{q} \bar{l} \rightarrow X } = (1+\varDelta _l)\varGamma _l \, . \end{aligned}$$

(7.63)

Thus direct and inverse decays produce the same sign of baryon asymmetry!