In this note we present an example of an extension of the Standard Model where unification of strong and electroweak interactions occurs at a level comparable to that occurring in the minimal supersymmetric standard model.
These are the notes of a set of four lectures which I gave at the 2012 CERN Summer School of Particle Physics. They cover the basic ideas of gauge symmetries and the phenomenon of spontaneous symmetry breaking which are used in the construction of the Standard Model of the Electro-Weak Interactions.
It is shown how grand unification can occur in models which are partly supersymmetric. The particle states which are composite do not contribute to the running of gauge couplings above the compositeness scale, while the elementary states contribute the usual large logarithmns. This introduces a new differential running contribution to the gauge couplings from partly composite SU(5) matter multiplets. In particular, for partly supersymmetric models, the incomplete SU(5) elementary matter multiplets restore gauge coupling unification even though the usual elementary gaugino and Higgsino contributions need not be present.
Compared to the minimal supersymmetric standard model, an extension by vectorlike fermions is able to explain the Higgs mass while retains the grand unification. We investigate the minimal vectorlike model by focusing on the vectorlike electroweak sector. We firstly derive the mass spectrum in the electroweak sector, then calculate the one-loop effects on the Higgs physics, and finally explore either vectorlike or neutralino dark matter. Collider constraints are briefly discussed.
We present the one-loop corrections originating from Quantum Chromo-Dynamics (QCD) and Electro-Weak (EW) interactions of Supersymmetric (SUSY) origin within the Minimal Supersymmetric Standard Model (MSSM) to the single-top processes bq -> tq and qbar q -> tbar b. We illustrate their impact onto top quark observables accessible at the Large Hadron Collider (LHC) in the t+jet final state, such as total cross section, several differential distributions and left-right plus forward-backward asymmetries. We find that in many instances these effects can be observable for planned LHC energies and luminosities, quite large as well as rather sensitive to several MSSM parameters.
A renormalizable non-Abelian theory of strong interactions of pions, mediated by rho-mesons, is formulated at tree- and at one-loop level in perturbation theory. Hadron masses are generated through spontaneous symmetry breaking using the Higgs mechanism. Quantization and gauge fixing is achieved using the generalized class of $R_xi$ gauges. As an application of this theory, pion-pion scattering lengths are obtained at tree-level in good agreement with data.
Roberto Frezzotti
,Marco Garofalo
,Giancarlo Rossi
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(2016)
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"A non-supersymmetric model with unification of electro-weak and strong interactions"
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Giancarlo Rossi
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