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
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
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
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
- Ph.D. Thesis of Wouter Dekens entitled "Discrete symmetry
breaking beyond the Standard Model", 2015.
- W. Dekens and D. Boer, "Viability of minimal left–right models
with discrete symmetries", Nucl. Phys. B 889 (2014) 727.
- Ph.D. Thesis of Wilco den Dunnen entitled "Polarization effects
proton-proton collisions within the Standard model and beyond", 2013.
- D. Boer, W.J. den Dunnen, C. Pisano and M. Schlegel, "Determining
the Higgs spin and parity in the diphoton decay channel", Physical Review Letters 111 (2013)
Boer and W.J. den Dunnen, "Bounding W-W' mixing with spin asymmetries
at RHIC", Physical Review Letters
- M.Sc. Thesis of Wouter Dekens entitled "A4 family symmetry", 2011.
- M.Sc. Thesis of Max Baak entitled "Anomalous W-fermion couplings;
theory and bounds", 2001.
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