Daniël Boer's Physics Webpage

Topic 2: Natural extensions of the Standard Model

Description & objectives:

There are multiple reasons to expect new physics beyond the Standard Model of elementary particles. However, so far we have no experimental indication for such new physics, therefore, theoretical investigations will have to follow general guiding principles such as the degree of symmetry and the degree of naturalness of the theory. It turns out to be very hard to find highly symmetric (but non-supersymmetric) theories that naturally, i.e. without fine-tuning, lead to the Standard Model at low energies. From our detailed studies of left-right symmetric models, that may be precursors of grand unification, we concluded that although the energy scales involved may be very natural, the ground state conditions demand an extreme amount of fine-tuning. The number of viable options is much more restricted than previously expected. These results likely carry over to GUTs in general and some mechanism to avoid this undesirable conclusion needs to be devised. This is one of the aims of this research line. In particular, this is studied for theories with extended Higgs sectors, which would at the same time offer more sources of CP violation (as do extended gauge sectors). The quest for theories beyond the Standard Model is in part based on finding an explanation of the asymmetry between matter and anti-matter observed in the universe that requires new sources of CP violation (among others). These have to lead to the baryon asymmetry in a natural way, otherwise one might as well impose fine-tuned initial conditions. Another goal of this research line is find a minimal mechanism to modify and extend the SM such that conformal symmetry is restored at high energies. This offers a way to protect the Higgs mass against receiving large quantum corrections, because the latter is considered unnatural. 



My research on this topic has in part been financially supported by the Dutch foundation FOM and the Ubbo Emmius Fund of the University of Groningen.