Theoretical Particle Physics at the University of Liverpool

Particle physics, also called high-energy physics, addresses the fundamental laws of nature which are revealed at the shortest distances or highest energies. Great progress has been made in this field during recent decades, both by large-scale and high-precision experiments and by research in theoretical physics. Our presently established knowledge is codified in the so-called Standard Model, a highly non-trivial quantum field theory (QFT) based on the mathematical concepts of gauge invariance and the Higgs mechanism (of which a crucial consequence, the Higgs particle, has not yet been found in experiment). There are strong reasons, including hints from cosmology - a matured field of research now intimately connected to particle physics - to assume that the Standard Model is not the ultimate description of nature even at energies accessible in the near future. Furthermore a new mathematical framework, for which string theory is the leading candidate, appears to be required for a consistent description of gravity and the other fundamental forces directly studied in particle physics. With the start of experimentation at the LHC at CERN, a proton-proton collider with a multi-TeV centre-of mass energy, high-energy physics has now entered what promises to become its most exciting phase in decades. The Theoretical Physics Group at the University of Liverpool - at this point comprising 9 full-time academic staff members, 3 full-time researchers (including one professor retired from admin and teaching) and 13 PhD students - is engaged in all aspects of particle physics relevant to the challenges indicated above. Our work can be described in terms of three research groups, mainly addressing 1. String and Beyond the Standard-Model (BSM) phenomenology and cosmology, 2. Higher- and all-order calculations in QFT, and QCD at colliders, 3. Low-energy hadron physics, lattice QFT and applications. String theory requires, for its mathematical consistency, the microscopic existence of more than the three macroscopic dimensions of space. Therefore a main challenge, taken up by members of group 1, is to understand the so-called compactification of these extra dimensions, with the aims of obtaining predictions at LHC energies and deriving their cosmological implications. Another important topic in string theory, also addressed by our group, is the description of black holes. Realistic string theories require a new high-energy symmetry called supersymmetry (SUSY), so another focus of our work is the study of supersymmetric extensions of the Standard Model. QFTs such as the Standard Model and its possible extensions (e.g. SUSY) are so complicated that they cannot be solved exactly. For scattering processes at colliders such as the LHC, the only known method is by successive approximations called perturbation theory, where the predictions of the theory are expanded in terms of a small parameter. This method is analogous to, but much more difficult than, the Taylor expansion of simple mathematical functions. Members of group 2 play an internationally leading role in such calculations, which are not only indispensable for the correct interpretation of the experimental results, but also for gaining structural insights which will guide further research. Perturbation theory is not applicable to many (e.g. static) quantities in the theory of the strong interaction (QCD) where the fundamental particles, quarks and gluons, are `confined' in hadrons (bound states such as the proton). Lattice theory, which uses a discontinuous space-time lattice on supercomputers, is the only `ab initio' method to address such quantities. The members of group 3 perform such computations and other studies relevant to confinement and non-perturbative contributions to observables, in particular the anomalous magnetic moment of the muon which at this point offers one of the most intriguing hints for BSM physics.

Particle physics and the closely related fields of particle astronomy and cosmology address some of the most fundamental questions in all of science. Experimental and observational facilities and research results for these topics have proved to be of great interest for the general public. While most of the specialized research in theoretical physics is neither `front page news', nor (unlike the development of experimental techniques) directly relevant to industry, it is nevertheless an indispensable part of fundamental science. Interpreting measurements at the LHC or cosmological observations in terms of fundamental concepts is impossible without theoretical research; and highly popular topics such as, e.g., quarks, Black Holes, the Higgs particle, strings and Dark Energy were first introduced as theoretical concepts. Many young people are motivated to study mathematics or physics by these fundamental topics. Thus the presence of leading research groups in fundamental science and their outreach programmes is important, especially to widen participation in structurally weak regions such as the North-West of England. Since 2006 our group has been organizing the Barkla lectures, a series with one well-publicized open lecture each year by an eminent scientist -- previous speakers include the Nobel laureates Wilczek, Veltman and 't Hooft. The funding of this successful series was originally provided by the university, but now requires new sources. Our group also participates in Cafe Sci (www.juniorcafesci.org.uk), an organisation which brings scientists into schools to lead a discussion about the topic of their research. The normal format is a brief introduction (10-15 minutes) by the scientist followed by 30-40 minutes discussion. For example, Mohaupt has visited Blue Coat School, Liverpool, in 2008 and Sts Peter and Paul School, Widnes, in 2009 to lead sessions on Black Holes. The Outreach Team of the Department of Mathematical Sciences, together with their colleagues in the other two departments (physics and chemistry) of the School of Physical Sciences of the University of Liverpool, run a vigorous outreach programme. During the academic year 2009-2010, the Outreach Team interacted with 14,000 pupils on 81 school visits. 40% of the schools were in areas having young peoples' Higher-Education participation rates within HEFCE's two lowest classification bands. There is evidence that this programme does substantially contribute to attracting pupils to the University of Liverpool. In partnership with the Physics Department as well as local schools, our Outreach Team plans to develop a set of `Maths in Physics' resources, which would in particular include activities looking at maths in particle physics. It is also planned to have additional talks for sixth formers by members of our group. Most of our PhD students leave academia after obtaining their degree. Taking part in our cutting-edge research, including international teamwork and
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conferences, provides them with much improved skills which are then transferred to their new area of work. These improvements include, e.g., the ability to solve non-routine problems independently, time and project management, communication and presentation skills and working partly in diverse teams; all of which are highly valued by employers outside academia. Destinations of our recent (and upcoming) PhD graduates include * Structural analyst, British Energy (nuclear power industry), Gloucester * Consultancy, Detica, Guildford (Surrey) * Audit, Deloitte, Liverpool * Software Development, Z+F UK (3D laser scanning) Manchester * Postdoctoral research, carbon capture and storage, Newcastle University * Pension actuary, KPMG, Manchester Furthermore two of our recent graduates entered teaching via the Graduate Teacher Programme, and will thus contribute indirectly to long-term science and innovation in the UK.