WHAT BREAKS

ELECTROWEAK SYMMETRY ?

We shall find the answer in experiments at the LHC?

Most likely it will tells us a lot about the physics beyond the SM

Electroweak symmetry breaking in the SM by the Higgs sector (renormalizable lagrangian)

SU(2)xSU(2) global symmetry of V :

Properties of the Higgs potential crucial forthe electroweak theory:

Spontaneously broken to the diagonal subgroup SU(2)

The Higgs mechanism then ensures that the Goldstone bosons become the longitudinal modes of the gauge bosons W,Z which acquire masses.

Renormalizability not crucial for EWSB

But crucial for ensuring unitarity of e.g. WW scattering by exchange of one physical Higgs particle h

INDEED,

In the Standard Model, the EWSB is described butnot explained

Can we better understand the Fermi scale? e.g. calculate it in terms of some more fundamental parameters?

The hierarchy problem of the Standard Model.

SUPERSYMMETRY ------MANY VIRTUES

Higgs sector of the MSSM:two Higgs doublets;

Fermi scale calculated in terms of the soft supersymmetry breaking parameters; generated by quantum corrections to the Higgs potential due to the large top quark mass(Ibanez, Ross)

The lightest physical scalar has similarproperties as the Higgs particle in the SM;

DOUBLE PROTECTION FOR THE HIGGS POTENTIAL

SUPERSYMMETRY PLUS LOW ENERGY GLOBAL SYMMETRY;

NO STRONGLY INTERACTING NEW PHYSICS

Prediction – new fermionic states needed by global symmetry,

e.g. new top quark around 1 TeV

Non –supersymmetric „solutions” to the origin of the Fermi scale.

Revival of those approaches inspired by various theoreticalideas (extra dimensions, AdS/CFT correspondence, deconstruction,…

General picture –new strong interactions that provide a low-scale cut-off to the (non-renormalisable) electroweak theory and are responsible forelectroweak symmetry breaking

Well-known example : rescaled QCD (technicolour)

Barrel organ: the power source is commonly assumed to be a crank, turned by the operator or by his monkey.

A barrel organ player has been asked how to compose good music.

Just smoothly turn the crank, he replied.

CONCLUSION

Supersymmetry – elementary scalars

Minimal supersymmetric model – renormlizable extension of the SM

UV behaviour improved due to fermion-boson cancellations;

Superpartner masses- cut off in the SMHiggs potential

The impact of physics beyond the Standard Model on precision electroweak data can be studied in a modelindependent way by adding to the SM lagrangian higher dimension operators

In the Standard Model(with a Higgs particle –renormalizable theory) from the fits to LEP data we get