Colour confinement

The term confinement indicates that coloured free particles do not exist in Nature. Besides valence quarks, a hadron contains a population of more quarks and gluons. From the (b) side of the Figure in the previous post (*) it is possible to infer that the strong interaction between two quarks enhances with the increasing of their … Continue reading Colour confinement

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The Minimal Supersymmetric extension of the Standard Model (MSSM)

The starting point for the construction of the Lagrangian of a such model is the SUSY Lagrangian, where the gauge invariance with respect to the group of the SM, , has to be imposed. In the minimal hypothesis, each particle included in the SM possesses a unique superpartner, i.e. formally a superfield has to replace … Continue reading The Minimal Supersymmetric extension of the Standard Model (MSSM)

Supersymmetry

Supersymmetry (SUSY) is one of the most compelling possible extensions of the Standard Model of particle physics, and one of the most promising theory candidate for a new principle about Nature that could be discovered at high-energy colliders such as the . The hierarchy problem represents the only indicator of the energy scale in which … Continue reading Supersymmetry

Beyond the Standard Model

After the discovery of a Higgs boson, all the particles included in the SM have been experimentally observed. Despite its extraordinary phenomenological success, the SM is considered an incomplete theory. It manifests some theoretical underlying problems which suggest the need for a "deeper" theory of which the Standard Model could be just an effectual theory. Furthermore, … Continue reading Beyond the Standard Model

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

Symmetries

Fields with physical significance are those that verify the Euler--Lagrange equations, or that satisfy the Hamilton's principle. For such systems, a general and systematic procedure is available to establish conservation theorems and constants of motion, as a consequence of invariance properties. Thus, conservation laws and selection rules observed in Nature may be imposed as symmetries of … Continue reading Symmetries