Download Slides - Indico

17.03.2006
B. Majorovits
Sphalerons and heavy Neutrinos:
An attempt to explain Baryogenesis
through Leptogenesis
Q1
L1
H
L2
L3
B+L
Q2
Nr
Nr
l
Q3
H
l
17.03.2006
B. Majorovits
OUTLINE:
• The Baryon asymmetry in our universe: Observations
• The Sakharov conditions for Baryogenesis
• Baryon Asymmetry in the Standard Model: Sphalerons
• Baryogenesis by Leptogenesis through heavy Neutrinos
Literature:
1. J.M. Cline, Spektrum der Wissenschaft, Nov. 2004
2. W.Buchmueller, R.D. Peccei, T.Yanagida, Ann.Rev.Sci.
55(2005)311
3. M. Trodden, XXIII SLAC Summer Inst, hep-ph/0411301
17.03.2006
B. Majorovits
OBSERVATION:
There seem to be more Baryons than Antibaryons in our
universe: We do not annihilate with our neighbours!
- No evidence of annihilation
regions in the visible universe
(galaxy clusters, local group)
- CMB spectrum unperturbed
with respect to matter antimatter annihilation (WMAP)
(edge of the visible universe)
- No cosmic anti-nuclei-flux
(D, He, C) detected (AMS)
17.03.2006
B. Majorovits
Baryon Density in our universe: CMB
CMB power spectrum is
sensitive to Baryon content of
our universe
http://space.mit.edu/home/tegmark/cmb/movies.html
WMAP measurements suggest:
Ωbh2 = 0.024 + 0.001
17.03.2006
B. Majorovits
Baryon Density in our universe: BBN
Abundance of light elements strongly
dependent on baryon to photon ratio
Remarkable consistency between
BBN and CMB. Combined Analysis:
 =
nB  nB
n
 (6.1  0.3) 10
10
For each 2 *109 photons there is one
baryon (proton or neutron)
D. Kirkman, et al. astro-ph/0302006
In the early Universe’s hot plasma: for
each (109+1) particles there are about (109
+0) antiparticles
But how was this asymmetry created?
17.03.2006
B. Majorovits
The Sakharov Conditions:
B-non conservation: If Baryon number would be
conserved, no Baryon asymmetry whatsoever could be
produced.
C & CP non conservation: If C would be conserved,
no asymmetry between particles and antiparticles could be
created
If CP would be conserved there would be no asymmetry
between left handed particles and right handed antiparticles,
thus also no particle-antiparticle asymmetry
Deviation from thermal equilibrium: If all
processes are always in equilibrium, processes that create
asymmetry would be in equilibrium with processes that
make symmetry  No creation of asymmetry possible.
17.03.2006
B. Majorovits
GUT Baryogenesis: Decay of
Superheavy Boson:
At GUT scale a superheavy Boson X out of thermal
equilibrium could decay through a CP violating decay:
Assume the decay probabilities:
1. P (X  u + u) = 0.51, P (X  d + e+) = 0.49 but
2. P (X  u + u) = 0.49, P (X  d + e-) = 0.51
 Effective Baryon production-rate of processes:
1. (2/3 x 0.51)-(1/3 x 0.49)
= 0.177
2. (-2/3 x 0.49)+(1/3 x 0.51) =-0.157
}
One net Baryon is created
per 50 X + X decays
17.03.2006
B. Majorovits
Baryon Asymmetry in the
Standard Model:
Unification of forces at GUT scale
 Leptons and Baryons equivalent for T > TGUT
 Baryon number violating processes in the SM!
Due to chiral nature of SM we have non vanishing divergences
in lepton and baryon currents: ∂μ JBμ = ∂ μ JLμ ≠ 0
Degenerate vacua have different Chern Simons numbers NCS.
These are related to Baryon and Lepton Number:
NfΔNCS= ΔB=ΔL where Nf=3 (number of generations).
 B+L violation!
But we still have ∂μ (JBμ - JLμ )=0  (B-L) conservation!
17.03.2006
B. Majorovits
Baryon Asymmetry in the
Standard Model:
uc + dc + cc  d + 2s + 2b + t + νe + νμ + ντ ΔB=ΔL=3
Q1
Sphaleron transition
for T > TEW
Energy
Degenerate vacua
with different
Baryon
L1 Numbers
L2
B+L
Q2
Instanton transition through tunneling
L3
Q3
ΔB=ΔL=3
Instanton rate ≈ 10-160
NCS
Sphaleron processes: 3Leptons +
3 Quarks of each generation make
B+L violating process:
In thermal equilibrium for
TEW≈100 GeV < T < 1012GeV:
Any existing asymmetries are
eaten by Sphalerons
For Baryogenesis before TEW (at
GUT scale) we need asymmetry
that will not be washed out
 B-L violation necessary!
17.03.2006
B. Majorovits
Have you ever met a Sphaleron?
L3
Q3
L2
This is where
the B+L
violating
Q3 process is
happening
L1
B+L
Q2
17.03.2006
B. Majorovits
Baryon Asymmetry in the Standard Model:
Electroweak Baryogenesis: Condensation of Higgs-field:
Higgs phase
m>0
symmetric phase m=0
17.03.2006
B. Majorovits
Baryon Asymmetry in the Standard Model:
Outside bubbles where Higgsfield has not yet condensated:
Sphaleron processes much more
likely!
Transition of particles from Higgs
phase to massless phase does
violate CP.
In Higgs phase sphaleron
processes are out of equilibrium
for TC<ΔυF(TC), where ΔυF is
jump in Higgs mass expectation
value. Valid for Mhiggs< 50 GeV
 Baryogenesis
Problem: Higgs mass is too large
(> 114 GeV) !  Created Baryon
asymmetry is immediately eaten
by hungry sphalerons!
17.03.2006
B. Majorovits
Leptogenesis:
It seems very difficult to explain Baryogenesis directly
Extension of SM: Right handed neutrinos (Majorana Singlet) are
required for consistency of the theory! They could also explain low
effective neutrino mass through see-saw mechanism!
l
H
H
H
H
Nr
Nr
N
+ r
+ Nr
H
l
l
l
l
P(Nr l H)=1/2(1+ε)P Decay of heavy right handed neutrino has
CP violating term through interference
P(Nr l H)=1/2(1-ε)P
between one loop diagram and self
B-L and CP violated
absorptive term
In 0νββ a right handed neutrino is absorbed in one vertex!
17.03.2006
B. Majorovits
Baryogenesis through Leptogenesis: How it could work
 Create Lepton-asymmetry that is transferred by sphalerons
to a Baryon-asymmetry
Indeed calculations show
that the right Baryonasymmetry could be
produced
B
Net Baryon
production:
Existence of a small
neutrino mass is in favor
of this hypothesis (see saw
mechanism)
{
Baryogenesis
ΔL: Neutrino decay L
We have direct connection
to Neutrino Physics!
17.03.2006
B. Majorovits
CONCLUSIONS:
• There is a matter-antimatter asymmetry in the visible universe
• There exist Baryon–number violating SM-animals: Sphalerons
(B+L) violating
HUNGER !
• Sphalerons could create Baryon-asymmetry at condensation of
Higgs field (CP-Violating), but in SM Higgs mass is too high,
(SUSY??)
• Baryon-asymmetries before TEW are eaten by hungry Sphalerons
• Leptogenesis by decay of heavy right-handed Neutrinos (B-L &
CP violating) could create Baryon asymmetry with the help of
Sphalerons