Theoretical Physics, then Mathematics, at Trinity College Dublin 2006-2010
Part III of the Mathematical Tripos at University of Cambridge 2010-2011
PhD at University of Cambridge 2011-2015
postdoc at Vrije Universiteit Brussel 2015-2022 and IFT Madrid 2022-2025

papers on string theory

What did I do? (roughly)
Geometry is the study of shapes and their symmetries. A square looks exactly the same if it is rotated by 90 degrees, while a circle is more symmetric: it is preserved by any arbitrary rotation. The universe itself can be thought of as a ``shape''. This shape has to be described using a more mathematically complex notion of geometry, in which the three space directions are combined with the direction of time. The shape of the universe dictates the force of gravity experienced by its inhabitants.

It makes sense to use this geometric picture to describe ``large'' features of the universe like solar systems, black holes and galaxies. Small features like atoms and their constituent particles instead require the ruleset of quantum mechanics. Reconciling these rules with those of gravity leads to thorny theoretical problems. A consistent way out of these problems is provided by string theory, where (in a nutshell) fundamental subatomic constituents are modelled not as point particles but strings. String theory then provides the best framework for understanding the physical laws of all possible universes. What shapes can these universes be? Often it's a good approximation to just use the familiar geometrical picture I described above. But there are extra symmetries, called dualities, in string theory which say a universe of one shape is the same as a universe of another. In a simple example, a circle of a given radius R can be ``rotated'' into a circle of radius 1/R.

Much of my research focused on new ``stringy'' geometrical frameworks where these dualities are not extra exotic features but appear naturally embedded as part of the framework itself. In terms of the simple circle example just mentioned, this means developing a geometry that knows simultaneously about the shape of both the first circle of radius R and the dual circle of radius 1/R: the fun way to try to do this is to incorporate the latter as a sort of special extra direction in the universe. I helped develop these frameworks, showing that you could use them to write down and begin to understand the physical properties of string theory universes which would be regarded as impossible in the conventional picture. I also showed how to use this approach as a unified entry point to access different subvariants of string theory (by treating conventional geometric universes as corresponding to different ``slices'' of the new, larger stringy geometry).

Later on, I was particularly interested in a set of such subvariants where the unification of space and time directions is undone. These are an interesting playground to explore different aspects of string theory, and my research showed in particular that they lead to a new and surprisingly natural geometric way to think about the appearance of the most studied notion of duality in string theory, known as holography (which says that a higher-dimensional theory of gravity is physically equivalent to a lower-dimensional theory without gravity).

slides on the non-Lorentzian geometry of holography: slides

notes accompanying a journal club introduction to Matrix Theory: notes

slides for an online talk to the TCD Theoretical Physics Society during lockdown in 2020, about what it's like being (trying to be?) a theoretical physicist: slides

links to some research talks:

random talk generator