Gauge Theories and Strings in the LHC Era

The standard model of particle physics encodes our current knowledge of the fundamental constituents of atoms and the nature of matter in the earliest moments following the Big Bang. However, our understanding of the dynamics of the standard model is limited by our ability to solve its strongly-interacting sector, quantum chromodynamics (QCD), which describes the interactions of quarks and gluons. The Swansea group is approaching this problem from two complementary perspectives. By approximating the continuum of spacetime as a discrete lattice of points, it is possible to simulate QCD on high performance computers. The group will study lattice QCD in the extreme conditions of high temperature and density which existed following the Big Bang and which can now be realised in heavy-ion collisions at the Large Hadron Collider (LHC) at CERN. These investigations will be complemented by analytic insights arising from `gauge-gravity duality', a remarkable principle which relates the theories describing particle physics with properties of general relativity. The primary goal of the LHC is, however, to discover the new physics which is responsible for the generation of mass for the elementary particles. This `electroweak symmetry breaking' is the least understood part of the standard model. It may be due to the existence of a background field permeating spacetime, which gives mass to particles as they interact with it. The quantum fluctuations of this field would show up at the LHC as the famous Higgs boson. On the other hand, mass generation may be due to the existence of a new strong interaction at the TeV energy scale probed by the LHC, as described by a class of theories known in analogy with QCD as `technicolor'. Again, we are studying these theories using both gauge-gravity duality and lattice simulations. Particle physicists do not, however, believe that the standard model is the ultimate theory of nature. It is an example of a gauge theory, a theoretical framework which unifies quantum mechanics and special relativity together with the fundamental symmetries which physicists have discovered through decades of experiments with particle accelerators. A deeper unification appears possible with superstrings, which contain both gauge theories and gravity together with a new type of spacetime symmetry known as supersymmetry. The Swansea group is therefore complementing its investigations of LHC physics with research into the deeper structure of gauge fields and strings, using fundamental ideas such as gauge-gravity duality and `quantum integrability' in the search for the underlying principles behind our current theories of particle physics.

The Pathways to Impact document summarises the group's activities in the areas of Knowledge Exchange and Outreach. Knowledge Exchange is centred on the Lattice group's exploitation of HPC facilities, especially through the close involvement of the UKQCD collaboration with IBM and the development of the Blue Gene series of machines. The Swansea group has established a close contact with IBM Research at Yorktown Heights, running lattice code as a test application to evaluate computer performance and development. The group is also active in developing Grid technology. Outreach activities are focused in three areas - schools activities, popular lectures and media involvement. The group organises two activities for schools: Particle Physics Masterclasses with hands-on computer sessions using ATLAS software to analyse LHC events for 6th form students and annual Christmas Lectures for younger pupils. Group members give frequent public lectures, especially to local astronomy societies and science cafes. We have also exploited the publicity surrounding the start-up of the LHC, as well as the success of the Department's atomic physics group in the creation and trapping of atoms of antimatter at CERN, through a series of TV and Radio appearances as well as newspaper and magazine articles