Neutrinos are elementary particles that play a unique role in our understanding of fundamental interactions. They interact extremely weakly, are either very long-lived or stable, and have very small masses compared to other particles such as electrons and quarks. It is the issue of neutrino mass that motivates this research project.

The basic idea of radiative models is that neutrinos gain mass through subtle quantum mechanical effects involving as-yet undiscovered, very massive particles. Because the required new particles are very massive, and the quantal effects so weak, the neutrino masses thus generated are very small.

However, it turns out that many radiative models are possible, which motivates a systematic study of their construction, leading to a systematic analysis of how these many possibilities can be searched for at the LHC and other experiments. CoEPP researchers have mapped out a way to accomplish this.

The experimental part of this research concentrated on testing a theory called the “type-III see-saw model”, which was proposed by University of Melbourne theorists in 1989. In common with the type-I and type-II see-saw models, this theory proposes that neutrinos are so light because their masses have an inverse relationship with a high mass scale corresponding to new particles that go beyond the Standard Model.

As the high mass scale, which is a free parameter, is made larger, the neutrino mass scale becomes lower. The see-saw theories are the simplest ways of explaining the anomalous lightest of neutrinos, and thus have received much attention over the years.


Image: Cern/Science Photo Library.