Symmetries of the QCD

An important feature of the QCD is the conspicuous amount of symmetries of its lagrangian. First and foremost, its lagrangian is invariant under local gauge transformations, i.e. one can redefine the quark fields indipendently at every point in the space-time, without changing the physical content of the theory. This determines a number of implications in … Continue reading Symmetries of the QCD

Supersymmetry Breaking

Supersymmetry in the equation for the MSSM Lagrangian is an exact symmetry. This implies the mass degeneration for the components of each supermultiplet. Anyway, if the superparticles had the same masses of the respective particles, they would have already been observed and the Supersymmetry should therefore be broken. Although it is widely believed that a … Continue reading Supersymmetry Breaking

The Higgs mechanism

The simplest way to implement the SSB in the electroweak theory is achieved by adding the Higgs field, a complex scalar isospin doublet with four degrees of freedom, Without affecting the gauge invariance, it is possible to add to the Lagrangian of the electroweak interaction (*) the term which indicates the SSB, with  and in the potential explicited … Continue reading The Higgs mechanism

Spontaneous symmetry breaking

One of the most important missing aspects of the SM theory has been for a long the origin of mass of fundamental particles. The Lagrangian of the full Standard Model (*) well-describes the interactions of matter and radiation, but it does not include any mass term for the introduced bosons, while fermion masses are put by hand via … Continue reading Spontaneous symmetry breaking