Fields, Strings and Lattices: From the Inflationary Universe to High-Energy Colliders

Research in particle physics and cosmology connects the largest scales, those of the Universe as a whole, with the smallest, namely those of fundamental particles and strings. By trying to understand how the Universe evolved after the Big Bang, we may gain insight into which particles are yet to be discovered at e.g. the Large Hadron Collider at CERN, and vice versa, a fascinating prospect!

It is commonly assumed that the early Universe went through a period of rapid expansion, dubbed inflation. The mechanisms underlying inflation can be investigated in a number of ways. In the so-called bottom-up approach, one aims to find predictions that are independent of details of models, but only depend on symmetries and the nature of the source of inflation. It is then possible to extract universal features leading to observational predictions and point towards physics beyond our currently known Standard Models of Particle Physics and Cosmology. In the complementary top-down approach, one starts with the given theory, e.g. one that is motivated by string theory, and derives its consequences, which, again might be testable by observations. These approaches can also be used to study the period of cosmic acceleration our Universe is currently going through, i.e. dark energy.

String theory is a theory of gravity (and other forces) operating at very high-energy scales. Besides its possible role as a fundamental theory, it has many intricate aspects which require a level of understanding deeply rooted in symmetries and dualities (a transformation that leads to two 'dual' formulations which are superficially very different but yet equivalent). By studying those, one may not only understand string theory better, but also arrive at dual theories which are relevant for e.g. physics beyond the Standard Model (BSM) probed at the LHC, especially if the BSM model is strongly coupled.

In order to make predictions for the LHC, it is necessary to perform very precise calculations, in BSM models and in the Standard Model itself. Some of these calculations can be done by expanding in a small parameter. This does not mean that the computation is easy though, since many scattering processes may contribute. However, it might be that by re-organising these contributions a new, more efficient, formulation can be found.

When there is no small parameter, a theory has to be solved as it stands. Often this can be attempted numerically, by formulating it on a space-time lattice. Since this involves very many degrees of freedom, typically one has to employ the largest supercomputers in the world. The theory of the strong interaction, Quantum Chromodynamics (QCD), is one of those theories in which a small parameter is absent. Although it is formulated in the terms of quarks (as matter particles) and gluons (as force carriers), these are not the particles that appear in the spectrum, which are instead protons, neutrons, pions etc. However, since QCD is so hard to solve, there may be other particles not yet detected and also not yet understood theoretically: examples are so-called glueballs and hybrid mesons. By studying QCD on the lattice, these ideas can be tested quantitatively.

A related question concerns what happens with all these particles when the temperature (as in the early Universe) or the matter density (as in neutron stars) is increased. Also this can be studied numerically and a transition to a new phase of matter at high temperature, the quark-gluon plasma, has been observed. Since this phase is currently being explored at the LHC, by colliding heavy ions, quantitative predictions on the spectrum and on transport properties, such as how viscous the plasma is, are needed here as well.

Some BSM models also lack a small parameter and hence are studied using similar lattice computing techniques. By scanning models with distinct features, again hints for the LHC may be found, e.g. with regard to unusual spectral features.

Swansea and Plymouth have a vibrant Impact Strategy which is demonstrated in our extensive public engagement programmes and linkages with industry.

The Swansea group's outreach programme spans school students, teachers and the public. We host Particle Physics Masterclasses utilising new software from our experimental colleagues' (CERN-based) antihydrogen experiment. 'Christmas Lectures' are organised where 600 GCSE and AS-level students listen to public engagement experts present cutting edge physics research. We host day-long preparatory workshops in Swansea University for students going to CERN on organised trips so that their experience in CERN is maximised. In addition, we present our work in the Welsh- language at the Eisteddfod (with STFC funding).

In Swansea we have impact on physics teaching in Wales through two programmes. In the first we present workshops to Physics teachers who go on trips to CERN organised jointly by the Welsh Education Department and the National STEM Learning Centre. These lectures give an introduction to the teachers and dovetail into the talks they receive during their CERN visits. The Welsh Education Department is using these workshops as templates for other organised visits by teachers to major Welsh industries such as Airbus and Tata Steel.

Also linked with the Welsh Education Department, we are producing video podcasts, tailor-made to mirror the Welsh Physics curriculum and the needs of teachers. The topics chosen are determined in consultation with the WJEC Exam Board and reflect the fact that many Physics teachers do not have degrees in this subject. In the future we plan to deliver interactive video conferences allowing two-way information flow with teachers to further develop our impact on Physics teaching in Wales.

In a major and ambitious initiative, Swansea University will be constructing a public-facing exhibition and outreach centre on a beach-front location as part of a major redevelopment of the city centre undertaken by Swansea City Council. It will showcase the University's Science research (including particle physics) and deliver wide ranging outreach programmes to schools. To prepare for this permanent space, we are commencing 'pop-up' exhibitions which will be sited in schools and vacant high-street shops. We are requesting funding for some particle physics-related kit for these displays. This will build on the knowledge and experience we have gained from the 'Swansea University Science for Schools Scheme'.

Plymouth will augment their ongoing outreach activities, such as the Big Bang fair in Birmingham's NEC, by initiating off- campus talks and demonstrations. These will particularly be based around a new portable planetarium which will feed into the public's innate interests in astronomy and for which we request funding.

Our Universities' Knowledge Exchange Programmes are based primarily on our lattice gauge theory research. Lucini, Patella and Rago have used a feature of their code which enables computation and communication to be independently stressed to develop an HPC benchmarking suite. This led to the formation of a company, BSMBench Ltd, which is developing this tool into a commercial product. Hands, Lucini and Rago have also forged close links with IBM Research Watson Labs in order to aid software development on HPC architectures.

Plymouth's HPC cluster is being used by marine engineers at the University (who are important for the local economy). Lucini is a member of HPC Wales whose aims are to 'deliver significant economic benefits across Wales'.

Furthermore, reflecting the 'Big Data' nature of lattice simulations, McNeile has set up a new grid certificate registration authority in Plymouth University which will aid the efficient transfer of large datasets between collaboration members, including those of the International Lattice Data Grid.