"Why do so many people love reading detective novels or playing online games imagining themselves as heroes in fantasy worlds?," asks Igor Ivanov, an FNRS researcher at the group “Fundamental interactions in physics and astrophysics” at the Ulg. "Because there is an enigma to be solved and it is part of human nature to be curious and to have it solved. In the same way, theoretical physics, in its purest form before any possible applications, is full of breathtaking enigmas concerning the fundamental structure of our world. The questions of nature to which we try to find the answers are a lot more complicated and interesting than those which others have imagined for us when writing a detective novel or programming a video game. In finding answers which touch on the fundamental structure of the world, there is more of a pleasure than of a challenge."

Particle physics aspires to describe the behaviour of elementary particles at the smallest possible scale and to understand the origin of their properties. But particles exist in the quantum world where they act both as waves and as particles. That is why theoretical physics associates with each particle a field whose lowest energy represents the state of the vacuum, whilst the particle itself results from an excitation of the field. This construction has grown into the so called standard model of particle physics, which allows for a remarkable precision in the description of particles and their interactions, observed in large accelerators. This model is based on the symmetry of electroweak interaction which existed in the very dense and very hot primordial universe and which was shattered when the temperature was no longer sufficient. Thus the standard model needs to be accompanied by a mechanism of spontaneous breaking of the electroweak symmetry.

Dozens of models have been constructed. The 'minimal' Higgs mechanism is a mathematically very simple model which predicts the existence of a new particle, called the Higgs boson. Other mechanisms are conceptually similar but introduce several Higgs bosons. Yet more are based on new concepts which can derive from more fundamental physics theories. As we can see, the mechanisms are numerous...and the corresponding physics predictions are different following the model adopted. The work of Igor Ivanov centers around a spontaneous symmetry breaking mechanism known as the two-Higgs-doublet model which stems from the theory of super-symmetry.