Talks

The generalized unitarity method reconstructs loop-level scattering amplitudes from tree-level scattering amplitudes. We review some of the steps of this method which are necessary for applications in any quantum field theory, discuss several points of view and emphasize some of the aspects that can be easily automated. We mainly use N=4 super-Yang-Mills theory to illustrate the discussion and comment on the necessary changes for applications to super-Yang-Mills theories with reduced supersymmetry.

Sarah Croke - is a postdoctoral researcher at Perimeter Institute. From Ireland and the UK originally, she received a BSc in Physics and Applied Mathematics from University College Cork, Ireland in 2003. After a brief stint as a radio astronomer, completing an MSc in Astrophysics, she studied Quantum Information and Quantum Optics under the supervision of Prof Stephen Barnett at the University of Strathclyde, UK, receiving a PhD in 2007. She has been a postdoc at PI since November 2007. She works in quantum information theory, and is interested in both theoretical and experimental aspects. Roger Colbeck - I completed my PhD in theoretical physics at the University of Cambridge in 2006, and was for one year a junior research fellow at Homerton College, Cambridge before moving to ETH Zurich in 2007. Having been a postdoctoral researcher there for two and a half years, I moved to Perimeter Institute, where I have been since. I do research in quantum information theory and quantum foundations.

A number of recent proposals for a quantum theory of gravity are based on the idea that spacetime geometry and gravity are derivative concepts and only apply at an approximate level. Two fundamental challenges to any such approach are, at the conceptual level, the role of time in the emergent context and, technically, the fact that the lack of a fundamental spacetime makes difficult the straightforward application of well-known methods of statistical physics and quantum field theory to the problem. We initiate a study of such problems using spin systems as toy models for emergent geometry and gravity. These are models of quantum networks with no a priori geometric notions. In this talk we present two models. The first is a model of emergent (flat) space and matter and we show how to use methods from quantum information theory to derive features such as speed of light from a non-geometric quantum system. The second model exhibits interacting matter and geometry, with the geometry defined by the behavior of matter. This is essentially a Hubbard model on a dynamical lattice. We will see that regions of high connectivity behave like analogue black holes. Particles in their vicinity behave as if they are in a Schwarzchild geometry. Time permitting, I will show our study of the entanglement entropy of the system, which suggests particle localization near these traps.

Throughout history science has aimed at unification, whereby more phenomena are explained by more fundamental theories with simpler principles. We will discuss how string theory aims at being the ultimate unified theory of all elementary forces in nature.