Particle Theory at the Higgs Centre

There are two types of fundamental forces in Nature: those responsible for particle interactions at subatomic scales and those responsible for the large scale structure of the universe. The former is described by Quantum Field Theories (QFT) such as the Standard Model(SM). Currently, our understanding of Nature at the most fundamental level is at the crossroads. In 2012, the LHC at CERN collided protons at higher energies than ever before, and observed sufficient collisions to find a significant excess, consistent with the Higgs boson of the SM. Over recent years it has become evident that this is indeed a SM Higgs, responsible for generating masses for vector bosons, leptons and quarks. Currently data at even higher energies is being taken at LHC, and it should soon become clearer whether there is more physics at the TeV scale, or whether we need to build machines capable of going to even higher energies. At large scales the European Planck satellite has given the most precise measurements of the cosmic microwave background (CMB) and it is an open question to determine the particle physics model best capable of describing the physics underlying the large scale properties of the Universe. In 2016 the detection of gravitational waves was announced by LIGO, marking the start of a new chapter in astrophysics. Thus at both small and large scales, this is a transformative time in fundamental physics. Our programme of research at the Higgs Centre for Theoretical Physics in Edinburgh is designed to be at the forefront of these new discoveries. Specifically, we provide theoretical calculations, using pen and paper, and the most powerful supercomputers, of both the huge number of background processes to be seen at LHC due to known physics, and the tiny signals expected in various models of new physics, in order to discriminate between signal and background, and thus maximise the discovery potential of the LHC. In parallel, we will attempt to understand the more complete picture of all the forces of Nature that may begin to emerge. The fundamental force responsible for large scale structure is described by Einstein's General Theory of Relativity (GR). During the last three decades, string theory has emerged as a conceptually rich theoretical framework reconciling both GR and QFT. The low-energy limit of String Theory is supergravity (SUGRA), a nontrivial extension of GR in which the universe is described by a spacetime with additional geometric data. Members of the group have pioneered approaches to deriving observable cosmological consequences of String Theory, to studying how the geometrical notions on which GR is predicated change at very small ("stringy") distance scales. The group is also engaged in using these theories to improve calculations in existing field theories. Recent discoveries of relationships between QCD amplitudes and GR, known as the 'double copy', offer new insight into gravitational phenomena. In summary, our research will impinge on both theoretical and computational aspects relevant to probing the phenomenology of LHC data, and will also encompass a wide range of topics in QFT and gravitational aspects of String Theory, impinging on cosmology, particle physics and on the very nature of physics itself.