3Discrete symmetries
III The Standard Model
3.7 Baryogenesis
In the universe, we observe that there is much more matter than anti-matter.
Baryogenesis is the generation of this asymmetry in the universe. Sakarhov came
up with three conditions that are necessary for this to happen.
(i)
Baryon number violation (or leptogenesis, i.e. lepton number asymmetry),
i.e. some process X → Y + B that generates an excess baryon.
(ii)
Non-equilibrium. Otherwise, the rate of
Y
+
B → X
is the same as the
rate of X → Y + B.
(iii)
C and CP violation. We need C violation, or else the rate of
X → Y
+
B
and the rate of
¯
X →
¯
Y
+
¯
B
would be the same, and the effects cancel out
each other.
We similarly need CP violation, or else the rate of
X → nq
L
and the rate
of
X → nq
R
, where
q
L,R
are left and right handed quarks, is equal to the
rate of ¯x → n¯q
L
and ¯x → n¯q
R
, and this will wash out our excess.