4th Generation Leptons inMinimal Walking Technicolor Theory
Matti HeikinheimoUniversity of Jyväskylä
Background: What is technicolor?
m H~ 2
In SM, electroweak symmetry is broken by the Higgs fieldHierarchy problem:Solution: Break electroweak symmetry dynamicallyTechnicolor = a new strongly interacting sector accounts for EWSB
Walking Technicolor
To get SM fermion masses, we need another new interaction at some high scale
This gives four-fermion vertices between SM fermions and techniquarks
→ Flavour changing neutral currents Need walking dynamics to suppress the FCNCs
ETC
Walking behaviour of the coupling constant as a function of momentum
Minimal Walking Technicolor Model
Fundamental techniquarks: needed for walking
→ Too large contributions to the S parameter
Adjoint techniquarks → Need only
N fTC=8
N fTC= 2
New particles: , ,
in the adjoint representation of
We have added three new weak doublets → the model suffers from Witten anomaly
Cure the anomaly: add one more weak doublet
→ 4th lepton generation , ,
Neutrino mass matrix allows the neutrino to have a general mass structure→ Two Majorana neutrinos ,
U L
D L U R DR
N L
E L N R ER
M L mDmD M R
1 2
SUTC 2
Phenomenology of the 4th generation leptons
The phenomenology of the 4th lepton generation has been studied, but usually with 4th QCD quark generation
MWTC adds only the 4th generation leptons but no QCD quarks
We also allow the new neutrino to have a general mass structure
The Lagrangian:
where , and
mass matrix eigenvalues
→ Mass eigenstates , where
Neutral current
Charged current
i LLDLLi E R
D ER i N R
D N R−me E LE R−
12
nLcM nLh.c.
E L= NE L
nL=N L
N Rc M=M L mD
mD M R
1,2=12
M LM R± M L−M R24mD
2
M 1=1 M 2=2 =± 1
=−1⇔ m D2 M LM R
W N L E L=cos 1LW E Lsin 2LW E L
Z N L N L=cos2Z 1L 1Lsin2Z 2L 2L
12
sin 2 Z 1L 2L 2L1L
Decay fractions of the Higgs boson in the standard model and in MWTC