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Strongly Coupled Systems

Final Report Summary - SCS (Strongly Coupled Systems)

Quantum field theory is the language in which the laws of physics is written. It is framework which governs large swathe of the world around us, from the interactions to elementary particles, to the properties of solids, to the structure of spacetime itself. It is also quite hard. When the quantum fluctuations become large, our understanding of these theory is still seriously lacking.

The purpose of this project was to find new tools to address these issues, both in high energy physics and in condensed matter physics. We tackled a number of different problems, often bringing in ideas from one area of physics to give a new perspective on problems in a totally different area.

A large part of the project focussed on a tool known as "holography". This maps problems in quantum field theory into problems of black holes. We wanted to understand very basic questions, such as :how do theories conduct electricity or heat? Rather remarkably, we can translate this into a problem of understanding the horizon of black holes. We made a number of breakthroughs, including how to make the horizon of a black hole look like the kind of lattices that one finds in solids. We derived universal formulae that govern the electrical and thermal conductivities of black holes, formulae that give promising new insights into poorly understood materials, like the strange metal phase of high temperature superconductors. We also understood how chaos propagates through black holes, again making surprising connections to strongly interacting materials.

In a separate development, we discovered a network of dualities in quantum field theories. A duality occurs when two quantum field theories, which look very different, actually describe the same physics. This is of practical use, because the questions that are difficult to easy in one theory are often easy in the other. In high energy physics, there are a huge number of these dualities, but all make use of a property called supersymmetry, something which doesn't seem to be of much use in condensed matter physics. We were able to show that a large class of these dualities persist even in the absence of supersymmetry. This has been extremely important in connecting a wide range of different ideas, from holography to quantum Hall physics to topological insulators.