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