Physics Beyond the Standard Model
Elementary particle physics is the study of the smallest components of matter and their mutual interactions. The mathematical language for describing such particles is that of quantum field theory, the result of merging the theory of special relativity with quantum mechanics. How to fully merge general relativity and quantum mechanics is still an open issue.

Higgs event For many decades we have had a working quantum field theory, the "Standard Model", providing a coherent picture of the world as built out of basic building blocks (quarks and leptons) interacting through the exchange of other particles called vector bosons. The last ingredient required for this theory to be complete, the Higgs boson, was discovered in 2012 at the Large Hadron Collider (LHC) at CERN.

Among the quarks there are those that make up the protons and neutrons found in the atomic nucleus. Among the leptons we find the electrons that, together with the nucleus, make up all the atoms in the periodic table. Finally, the prime example of a vektor boson is the particle of light itself -- the photon -- responsible for the description of electromagnetic interactions at the quantum level. There are other particles of each type, most of which are unstable and not found in ordinary matter, describing more exotic phenomena.

The experimental tools that have been used to test this construction comprise first of all of particle colliders, such as the LHC, where the energy of the colliding particles in the beam is converted into new heavy particles according to Einstein's well known relation between mass and energy. There have been also a number of highly valuable non-collider experiments that helped elucidating e.g. the nature of neutrinos (types of lepton).

LHC

The group is involved in theoretical attempts at formulating and testing an even more complete and overarching theory that would include phenomena beyond the Standard Model. There are many reasons to believe that such a theory can be formulated, perhaps the most compelling one being the existence of dark matter, a type of matter not present in the Standard Model, interacting very weakly with ordinary matter but whose presence can be inferred by its gravitational effects. Many models of physics beyond the Standard Model involve particles that could be candidate constituents of such dark matter component of the universe. These particles could also be produced in collider experiments and their properties studied in a controlled environment.

The theoretical activity is thus divided into a model building phase, where new ideas are implemented in a model typically involving new particles or new interactions, and a simulation phase, where the model is used to predict some experimental outcome and cross checks with the already available experimental data are performed.

The first phase relies for guidance on the notion of symmetry, namely on the existence of transformations amongst the objects of the theory that leave the theory unchanged. Such concept have been at the heart of many previously successful constructions, such as the theory of special relativity that can be based upon the postulate of invariance under space-time transformation known as Poincarè transformations. One of the most promising ideas to go beyond the Standard Model is to postulate the existence of a new symmetry enlarging the one above, so called Supersymmetry. This is a research area in which the group is very active.

At the phenomenological level, such symmetry (if realized in nature) predicts the existence of a new set of particles in addition to those of the Standard Model and also dictates many properties of their interactions. Such interactions can then be simulated on a computer and the outcomes compared with experiment. It is a true accomplishment of the Standard Model that it has so far passed all the collider-based tests, but the hunt continues!

Supersymmetry is not the only option on possible ways towards new physics. Other possibilities include e.g. models in which one or more of the particles currently regarded as elementary are in fact composite. As before, these models need to be formulated in a consistent theoretical set-up, then simulated and tested against currently available data. Even more exotic scenarios are possible and new ideas worth investigating are being generated all the time by a worldwide community of active researches to which the members of the group belong.