#### Transcript Slajd 1 - University of Oxford

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) Properties of the Higgs potential crucial for the electroweak theory: SU(2)xSU(2) global symmetry of V : 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 but not 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 similar properties 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 theoretical ideas (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 for electroweak symmetry breaking Well-known example : rescaled QCD (technicolour) CONCLUSION 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. Supersymmetry – elementary scalars Minimal supersymmetric model – renormlizable extension of the SM UV behaviour improved due to fermionboson cancellations; Superpartner masses- cut off in the SM Higgs potential The impact of physics beyond the Standard Model on precision electroweak data can be studied in a model independent 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