# Formal particle theory and string theory

Our group has research interests in more formal aspects of the quantum field theories that underly the Standard Model, and also many regimes in condensed matter physics. A focus of attention has been the low energy regime of strongly interacting theories such as QCD, for which we have limited theoretical control, particlarly over dynamical processes in finite temperature regimes. Study of effective field theories such as hydrodynamics, which relies on the underlying symmetries, is an important tool. In recent years, a number of insights into these theories has emerged from studying so-called "dualities". Examples include electric-magnetic duality in supersymmetric field theory, and in particular the general gauge-gravity correspondendence that emerged from string theory.

String theory remains perhaps our only consistent quantum theory of gravity. In this theory the fundamental building blocks of universe are not point particles but (at least perturbatively) they are open and closed strings. Quantization of string theory is highly constrained and naturally leads to the building blocks of the Standard Model, namely gauge thoeories, and also perturbative General Relativity as necessary ingredients. However, consistency conditions apparently also require supersymmetry and a spacetime of 10 dimensions. Therefore, string theories are naturally theories of extra dimensions combined with supersymmetry. Beyond providing an arena in which to study unified models of particle physics and gravity, string theory also provides us with another arsenal of tools with which to study the dynamics of gauge theories. In recent years a remarkable correspondence, or "duality", has been uncovered between gauge and gravitational theories, known as the AdS/CFT correspondence. This implies a non-intuitive interplay of these two seemingly quite different dynamical systems, and the correspondence has been used to provide powerful tools for understanding strongly-interacting field theories. As just one remarkable example, the hydrodynamic regime in finite temperature field theory becomes intrinsically tied to the dynamics of black hole horizons.

At the formal level, supersymmetry itself also provides us with a number of powerful tools for the study of gauge theories more generally, particularly in regimes where in the Standard Model we lack full analytic control. A prime example is the low energy regime of QCD -- the theory of the strong interactions, where quarks and gluons must bind to form the observed hadronic spectrum, comprising in particular protons and neutrons. The study of supersymmetric models of QCD can aid in providing a more detailed understanding of this dynamical regime.