Phenomenology

We are a group with overlapping interests in particle phenomenology, working to connect the results of high energy theory with high energy experiments. For a list of papers published by the current members of the phenomenology group, click here.

See below for an overview of our research interests. If you would like to know more, please contact Prof. Christoph Englert, Dr David Miller, Dr Sophie Renner, or Dr Dave Sutherland.

The layers of known particles organised by length scale, with the Standard Model particles at the smallest scales yet probed. We believe that particles beyond the Standard Model lie at even smaller scales.

Beyond the Standard Model physics

Particle physics is having a remarkable run. We probe ever smaller scales with more energetic experiments, peeling back the layers of matter from atoms, through to nuclei, their constituent hadrons, all the way down to the handful of particles that make up the Standard Model of particle physics. The Standard Model is the theory of quarks, leptons, gauge and Higgs bosons that comprise all known matter in the layers above it.

However, we are certain that the Standard Model is only an approximation to a more fundamental theory of particle interactions. Now we want to know what exists beyond the Standard Model (BSM) - what happens at even higher energies?

There are many possibilities, designed to answer outstanding puzzles: what is dark matter made of, why is there more matter than antimatter, what explains the hierarchies between the strength of electroweak interactions and that of gravity, or between the masses of the Standard Model particles themselves?

We study new mechanisms for explaining these puzzles, often embedded in the frameworks of supersymmetry, grand unified theories, and composite Higgs models, seeking to understand their experimental signatures.

The loop-level process, known as a penguin diagram, through which Bs mesons decay in the Standard Model

Flavour

Flavour physics concerns the properties, interactions, and decays of the different "flavours" of quarks (up, down, charm, strange, top, and bottom), of their composite particles (i.e., mesons and baryons built from quarks), and of different "flavours" of leptons (electrons, muons, taus and their respective neutrinos). How can we use the wealth of current and future data on these properties to look for evidence of fundamental particles beyond those that we currently know? This unites the interests of the lattice, phenomenology, and PPE groups here in Glasgow.

In the phenomenology group, we study how to use effective field theories to connect the flavour dataset in a model-independent way to higher energy electroweak and Higgs measurements, and also to search for light GeV-scale particles. We build models to explain the peculiar pattern of masses and mixings between the different particle flavours.

A cartoon showing how an interaction mediated by a heavy particle looks like a short-range interaction at large distances

Effective field theories

Effective field theories work on the fundamental principle that high momentum modes have short range effects. This is a powerful organisational and calculational tool for complicated field theories.

In particle physics, it means that to look for sufficiently heavy new particles, it suffices to look for new short range interactions among the particles that we already know about.

Within the PPT group, we work on: the phenomenology of these new interactions (what do we measure to see them at collider and other experiments?); the calculational tools (how to effectively predict the strength of these new interactions?); their fitting (what do measurements imply about the strength of the new interactions?), as well as the rich mathematical structures that these new interactions create within field and scattering theory.

The lagrangian of the Standard Model, with the Higgs field highlighted, together with a schematic plot of the Higgs potential, showing the Standard Model prediction together with an alternative prediction from some beyond the Standard Model theory

The Higgs and colliders

The Higgs boson, discovered in 2012, is fundamental to the Standard Model of particle physics. The Higgs is predicted to couple and give mass to every Standard Model particle. These couplings are now being measured ever more precisely in experiment.

Within the PPT group, we research the most effective measurements of the Higgs, and how to interpret them. For example, does the Higgs couple to anything else, such as dark matter? What new information can we extract from rare multi-Higgs and multi-top processes, and what techniques can we use to measure them?

Moreover, the nature of electroweak symmetry breaking - how the Higgs acquired its vacuum expectation value and gave mass to the particles of the Standard Model - is still unknown. We study what future multi-Higgs measurements and cosmological signatures of phase transitions in the early Universe can tell us.