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