The Universe at Extreme Scales

Lead Research Organisation: Swansea University
Department Name: College of Science

Abstract

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. By trying to understand how the Universe evolved after the Big Bang, we may gain insight into which particles are yet to be discovered, e.g. at the Large Hadron Collider (LHC), and vice versa.

Concerning the early Universe, it is commonly understood that it underwent a period of rapid expansion, called inflation. However, many open questions remain. For instance, what is the mechanism of cosmological inflation, and, can we link inflation to quantum gravity, a theory that still eludes us? Interestingly, the recent observations of gravitational waves may provide a guide here. Inflation predicts a gravitational-wave background with properties depending on the details of the inflationary model. Hence if this background is observed, it may help us to further uncover details of the inflationary epoch after the Big Bang. Gravitational waves may also shed light on other puzzles, namely those related to dark energy and dark matter. Again, possible alternative theories to Einstein's general theory of gravity, which are designed to solve the dark energy/matter puzzles, may leave their imprint in gravitational waves.

In contrast to this, the LHC probes the smallest length scales, by colliding protons and nuclei at very high energies. In order to test the Standard Model (SM), our current highly successful theory of elementary particles, to the extreme, it is necessary to compute SM processes to high precision, and make predictions of physics beyond the Standard Model (BSM). The former can be done using advanced techniques which go beyond the usual Feynman diagrams. For the latter, one may take the viewpoint that the SM is an effective field theory (EFT), valid up to a certain energy scale only. To understand which novel BSM interactions can give rise to the SM at low energies, without conflicting with high-precision tests from the LHC, is an outstanding challenge. Two main classes of candidate theories are so-called near-conformal gauge theories and Composite Higgs models, which both give rise to electroweak symmetry breaking and a light Higgs boson. They may even provide dark matter candidates.

These theories have a commonality with the theory of quarks and gluons, Quantum Chromodynamics (QCD), namely that they are strongly interacting. This implies that they cannot be solved easily analytically, but are amenable to numerical simulations on high-performance computing facilities. The study of QCD provides a link between the physics of the early Universe and elementary particles. Namely, as the Universe cooled down after the Big Bang, it underwent a series of phase transitions. During one of those, quarks and gluons combined into hadrons, i.e. the particles we observe today. The QCD phase transition is currently being explored at the LHC, by colliding heavy ions, motivating quantitative predictions on how the QCD spectrum changes with temperature. In fact, even understanding the QCD spectrum in vacuum is still partly unsolved and may guide toward BSM physics.

Quantum field theories (QFTs) describes physical processes across a vast range of energy scales, from fundamental interactions, as mentioned above, to low-dimensional and condensed matter systems. Many new phenomena and the detailed structure of QFTs are anticipated to lie beyond the confines of traditional perturbative methods or numerical simulations. Dualities provide links between hitherto unrelated theories, making tractable questions previously considered to be out of reach. With new dualities being discovered, the richness of QFT is larger than naively expected. Similarly, dynamics out of thermal equilibrium, the process of thermalisation, or the evolution of quantum information, relevant for black hole dynamics, benefits from new approaches, some of which are motivated by quantum information theory.

Planned Impact

Research carried out by the Swansea and Plymouth groups has significant impact, transforming people, the economy, knowledge, and society.

People - As part of our research programme, we train and supervise postgraduate students, funded by STFC or otherwise. This allows our students to develop a wide range of technical, numerical and problem-solving skills, which prepares them for employment, in academia, industry or elsewhere. The Swansea group is part of the STFC Centre for Doctoral Training (CDT) on Data-Intensive Science, jointly with Bristol and Cardiff. Via the CDT, we have ample contacts with external and industrial partners, including large international companies, locally based SMEs, and government partners. Networking and training activities by the CDT are generally open to non-CDT students as well.

Economy - Engagement with external stakeholders is delivered in various ways. The Environmental Futures & Big Data Impact Lab, recently set up in Devon, is a £6.4m part-funded ERDF project delivered by the Universities of Exeter and Plymouth, and other institutions in the Southwest. The central goal is to facilitate academics to work with Devon based SMEs, on projects involving big data and safeguarding the environment. The Plymouth team contributes to the management of the Impact Lab and advises on shaping the Big Data science group.

Research on lattice simulations of dynamics beyond the Standard Model (BSM) led to the development of BSMBench, an HPC benchmarking suite. BSMBench provides an overarching software benchmarking suite which can test the response of computing systems in a wide range of working environments. The impact of this work includes the creation of a start-up company, documented use from IBM in their supercomputers and a publication in the world's most read Linux magazine, making real impact in a global industry.

Knowledge - The Swansea lattice group is heavily involved with Supercomputing Wales, a new £15M investment by the European Regional Development Fund. It has a particular mission to create highly-skilled research jobs and build collaborative partnerships with the region's industries. This exciting initiative provides a step change in supercomputing-enabled research and development in Wales. A related initiative is the Swansea Academy for Advanced Computing (SA2C), which provides researchers based in Swansea with training and support from dedicated Research Software Engineers, enabling a continuous exchange of knowledge and sharing of best practice.

High-performance computing activities in Plymouth are organised via the HPC Centre. The lattice group share their HPC expertise on the HPC cluster with new users. The group has developed a series of Courses for Professional Development (CPD) aimed both at academia and private sector to extend the usage of these tools and facilities also outside the current core areas.

Society - The Swansea and Plymouth groups are very active in public engagement and outreach, with the aim to inform the general public and inspire younger people to take up science during their education.

Swansea University's Oriel Science has an established record of creative, inspirational and impactful public engagement. Since the launch in September 2016, we have interacted with over 40,000 people, including 17,000 in our city-centre pop-up, and received nearly £500k funding from Welsh Government, SU, STFC and EPSRC. We are currently establishing a permanent Oriel Science venue in the city centre.

Besides this, both groups run regular activities for school pupils and the general audience, including Physics Christmas Lectures, Particle Physics Masterclasses, astronomy shows in the Plymouth Planetarium, and the Festival of Physics. The Swansea group will launch, in March 2019, the annual David Olive Distinguished Lecture series, with Robert Dijkgraaf, Director of IAS Princeton, as inaugural speaker.

Publications

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