Theoretical Particle Physics

Particle physics addresses the fundamental laws of nature which are revealed at short distances or high energies. Great progress has recently been made in this field, both by large-scale, high-precision experiments and by theoretical research. Our current knowledge is encoded in the "Standard Model", a theory based on the mathematical concepts of gauge invariance and the Higgs mechanism which predicts the Higgs boson.

There are strong reasons, including hints from cosmology and the anomalous magnetic moment of the muon, to believe that the Standard Model (SM) 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 studied in particle physics. The challenge of discovering the ultimate description of particle physics can be addressed from two sides: by performing high-precision analyses of the wealth of data being produced by the Large Hadron Collider (LHC) and other particle physics experiments, in order to seek the imprint of such an underlying theory; and by showing how string theory naturally leads to the Standard Model. Our group is in the vanguard of both these approaches.

String theory requires, for its mathematical consistency, the microscopic existence of more than the three macroscopic dimensions of space. Therefore a main challenge is to understand how the so-called compactification of these extra dimensions can lead to a theory of the form of the SM, possibly accompanied by additional predictions at LHC energies, and cosmological implications. An intermediate stage in this process is usually a supersymmetric version of the Standard Model, which we expect would reveal itself at high energies, Beyond the Standard Model (BSM) -- but perhaps accessible at LHC run 2. Supersymmetry postulates that the particles which constitute matter (fermions) and transmit forces (bosons) are related; the main attraction of the concept is that it explains the minute masses possessed by fundamental particles. Another important topic in string theory, also addressed by our group, is the description of black holes. This places in sharp relief the challenges of reconciling gravity and quantum physics.

Quantum Field Theories (QFT)s such as the Standard Model and its possible extensions (e.g. supersymmetry) 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. Members of our group 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.

Although the interactions in a collider are between fundamental particles such as quarks, individual quarks are never observed as reaction products. They are only seen combined as hadrons consisting of 2 or 3 quarks, bound together by the "strong interaction" -- a phenomenon called quark confinement. It thus becomes vital to understand confinement and the strong interactions, in order to reconstruct the interactions in colliders from the reaction fragments. This requires novel techniques as most particle physics computations are based on the interactions being weak (as described above). The most effective such technique is the simulation of spacetime by a lattice of discrete points. Our group is involved in the use of high performance computing for this purpose and is especially interested in lattice simulations of hadrons. We are also interested in theoretical mechanisms for confinement.

1. Many young people are motivated to study mathematics or physics after being inspired by fundamental topics in particle physics or cosmology such as black holes, string theory or the Higgs discovery. 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. The major potential beneficiaries of our research are therefore the public in our region, especially school students and young people. Our programme of public engagement and outreach is ongoing and continuous, so the most effective way of describing the potential benefits is to list recent activities in the expectation that they will continue to be equally successful.

(a) Since 2006 our group has been organizing the Barkla lectures, a series with an annual open lecture by an eminent scientist. Previous speakers include the Nobel laureates Wilczek, Veltman, 't Hooft and Englert. This year's speaker was Katherine Freese, an eminent cosmologist currently Director of Nordita. The lectures attract a large audience including undergraduates and members of the public.

(b) Our group also participates in Cafe Sci, an organisation which brings scientists into schools to lead a discussion about their research topic. For instance, Tatar led a session on String Theory in Jan 2013 in a Liverpool hotel. We also take part in the "STEM ambassador" programme (see www.stemnet.org.uk). Teubner took part as floor manager in the ``Big Bang Day'' at Aintree in June 2014 and 2015. Langfeld regularly contributes to the STFC Particle Physics Masterclass. He frequently gives talks to secondary school students on topics such as Particle Physics and The Quantum World, and also presents public talks such as recently to the British Computer Society (BCS) on Quantum Cryptography.

(c) A recent PhD graduate (Jaclyn Bell) gained £25000 of government funding for an Outreach project during her PhD and is a scientific advisor at the STFC Educational Hub at the Low Gillerthwaite Field Centre in Cumbria; and also at the Catalyst Science and Discovery Centre in Runcorn with which STFC is in partnership.

(d) An exciting development recently has been the presence of a Leverhulme-trust funded "Artist in Residence" Dr Emily Howard who is composing musical works inspired by research in our department. One of these (based on pure maths research) has been performed and recorded already. She has had many discussions with Jones and group members on supersymmetry and other topics, which we hope will lead to further compositions based on our group's research. Jones also participated with Dr Howard in a filmed Arts and Sciences Forum on the Creative Process.

2. Using our expertise in numerical simulations, our group engages with industry to solve engineering problems. Langfeld works with Research Instruments examining the effect of laser biopsies on human embryos. Also Langfeld and collaborators are working on simulations of airflow through realistic airfilters.

Most of our PhD students leave academia after gaining the PhD. Taking part in our cutting-edge research, including international teamwork and conferences, provides them with skills which are then disseminated in their new area of work. These improvements include, for example, the ability to solve non-routine problems independently, time and project management, communication and presentation skills and team-working ability; all of which are highly valued by employers outside academia. The University provides a graduate training programme designed to enhance and complement these transferable skills which also includes careers workshops.

Destinations of our recent PhD graduates include Software Development, Dorset Software; Postdoctoral research, carbon capture and storage, Newcastle Uni; Pension actuary, KPMG; Forecaster, Met Office; Researcher, Defence Science and Technology Laboratory.