Particles, Fields and Spacetime

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All matter in the universe and the fundamental forces apart from gravity appear to be well described by particle theories, in which the fundamental components of matter are pointlike particles, which interact by exchanging other kinds of particles. Quantum field theory is the mathematical language describing these particle theories; the particles describing forces are described by a class of theories called gauge theories. However, it appears we need to go beyond quantum field theory to include gravity. The leading candidate for this extension is string theory, which is based on the idea that the particles are actually one-dimensional loops of string, with the interactions described by smooth surfaces connecting different strings. One strand of our research is the development of new tools for computations in quantum field theory. In one line of research, it has been understood that certain gauge theories have additional previously unsuspected symmetries, which explain the mysterious simplicity of some computational results. This has been developed to obtain more efficient calculational techniques for increasingly general questions. In an independent line, a symmetry called conformal symmetry has been newly exploited to constrain the particle content and interactions of theories with this symmetry. We aim to develop these tools further and bring them together with the long-term goal of completely solving the simplest, most symmetric theories. We also have a broad programme of research on aspects of field theory far from the vacuum, including work on smooth classical solutions (solitons) and their moduli spaces, and special classes of field theories where the theory is completely solvable (integrable models). Work on string theory has led to the discovery that some quantum field theories can be related to string theories in a space with more dimensions; this is referred to as holography. Some difficult questions in the field theory can be mapped to simpler questions in the higher-dimensional space. This also provides a new perspective on string theory, which can be used to deepen our understanding of gravity. We are studying the application of these techniques to field theories used to study interesting new phases of matter, and we are exploring the role of intrinsically quantum mechanical features of the field theory in the emergence of the higher-dimensional geometry. Cosmology is the study of the very early universe. This has a long history of fruitful interaction with particle theory, and we are developing this further, relating new developments in field theory to cosmological observations. For example, we are studying the role of the Hiss boson recently discovered at CERN in cosmological evolution.