New Ideas in Gauge, String and Lattice Theory

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


The standard model of particle physics encodes our current knowledge of the fundamental constituents of atoms and the nature of matter in the earliest moments following the Big Bang. However, our understanding of the dynamics of the standard model is limited by our ability to solve its strongly-interacting sector, quantum chromodynamics (QCD), which describes the interactions of quarks and gluons. The Swansea and Plymouth groups are approaching this problem from two complementary perspectives. By approximating the continuum of spacetime as a discrete lattice of points, it is possible to simulate QCD on high performance computers. The groups will study lattice QCD in the extreme conditions of high temperature and density which existed following the Big Bang and which can now be realised in heavy-ion collisions at the Large Hadron Collider (LHC) at CERN. These investigations will be complemented by analytic insights arising from `gauge-gravity duality', a remarkable principle which relates the theories describing particle physics with properties of general relativity.

The primary goal of the LHC is, however, to discover the new physics which is responsible for the generation of mass for the elementary particles. This `electroweak symmetry breaking' is the least understood part of the standard model. It may be due to the existence of a background field permeating spacetime, which gives mass to particles as they interact with it. On the other hand, mass generation may be due to the existence of a new strong interaction at the TeV energy scale
probed by the LHC. In both cases, the theories predict the existence of a new spin zero particle, the famous Higgs boson recently discovered at the LHC. Distinguishing these possibilities is a subtle problem and once again we are attempting to resolve the question using both gauge-gravity duality and lattice simulations.

Particle physicists do not, however, believe that the standard model is the ultimate theory of nature. It is an example of a gauge theory, a theoretical framework which unifies quantum mechanics and special relativity together with the fundamental symmetries which physicists have discovered through decades of experiments with particle accelerators. Meanwhile, gravity remains outside this framework, being described by general relativity in terms of the curvature of spacetime. A deeper unification appears possible with superstrings, which contain both gauge theories and gravity together with a new type of spacetime symmetry known as supersymmetry. The Swansea group is therefore complementing its investigations of LHC physics with research into the deeper structure of gauge fields and strings, using fundamental ideas such as gauge-gravity duality and `quantum integrability' in the search for the underlying principles behind our current theories of particle physics.

Planned Impact

The Pathways to Impact document summarises the activities of the Plymouth and Swansea groups in the areas of Knowledge Exchange and Outreach.

Knowledge Exchange is centred on the exploitation of HPC facilities, especially through the close involvement of the UKQCD collaboration with IBM and the development of the Blue Gene series of supercomputers. The Swansea group has established a close contact with IBM Research at Yorktown Heights, running lattice code as a benchmark application to evaluate computer performance and development. This has led to the creation of a third-party company, BSMBench Ltd, to commercialise a benchmarking tool developed from the group's research in lattice gauge theory. Through UKQCD, both groups are active in developing Grid technology.

Outreach activities are focused in three areas - schools activities, popular lectures and media involvement. The Swansea group organises two activities for schools: Particle Physics Masterclasses for 6th form students with lectures and hands-on computer sessions using ATLAS software to analyse LHC events, and annual Christmas lectures for younger pupils. Group members give frequent public lectures and organise the local Swansea `Science Cafe'. The excitement surrounding the first experimental results and discovery of the Higgs boson at CERN, as well as the achievement of the Physics Department's atomic physics group in creating and trapping atoms of antihydrogen at CERN, have been exploited in numerous TV and radio presentations as well as in newspaper and magazine articles. The keynote lecture by Peter Higgs at the `Strong and Electroweak Matter' conference in Swansea in July 2012 was streamed to schools across the U.K. and an interview with Peter was posted on the University's website and You Tube.
Description The research group has made significant progress on all the topics proposed in the "New Ideas in Gauge, String and Lattice Theory" grant, with almost 200 papers being published in the grant period. A selection of highlights include:

Quantum Field Theory and Gravity:
A new mechanism - 'radiatively induced gravitational leptogenesis' - was developed to explain the matter-antimatter asymmetry of the universe, exploiting subtle features of gravitational interactions with the quantum self-energy cloud of the light neutrinos.
Holography: Non-abelian T duality in holographic theories was shown to generate new solutions of string and M-theory exhibiting novel physical (Wilson loop, symmetry breaking, central charges) and geometric (AdS factors, G structures) features. Holographic conformal field theory was used to calculate the thermodynamic and entanglement entropies of conformal field theories with higher spin charges.

It was shown that the AdS5 x S5 string theory admits an integrable deformation for which the worldsheet theory is a WZW model based on a subgroup, extending previous analyses of the S-matrix in these theories.

The development of improved unitarity and augmented recursion techniques allowed the calculation of a range of new one and two-loop amplitudes including the 1-loop, 6-point NMHV amplitude in N=4 supergravity and the 2-loop, 6 gluon all-plus helicity amplitude in QCD.

Beyond the Standard Model:
The existence of a light Higgs-like scalar particle, a pseudo-dilaton, has been revealed and studied in a class of holographic BSM models. Seiberg duality was extended to non-supersymmetric gauge theories, allowing an analytic non-perturbative investigation of strong-coupling phenomena including the range of the conformal window.

Hot and Dense Lattice:
The FASTSUM lattice collaboration (supported also by grants from DIRAC, PRACE and Hartree HPC) has demonstrated the melting properties of different heavy-quarkonium states across the deconfinement phase transition in QCD at high temperature, results of importance to the LHC heavy-ion programme. Improved, detailed studies were made of the
spectral functions determining transport coefficients in QCD, with new results for the electrical conductivity and charge diffusion coefficient consistent with expectations from holographic models. The first applications to QCD at non-zero baryon density were made using the complex Langevin approach to the 'sign problem'.
BSM Lattice: It was demonstrated through lattice investigations of SU(2) gauge theories with Dirac adjoint quarks that near-conformal gauge theories can exhibit large anomalous dimensions, a potentially key ingredient for realistic strong-coupling BSM models of electroweak symmetry breaking.
Exploitation Route This research is an integral part of the ongoing UK and international activity in particle theory. The topics addressed and resolved will inform the work of particle theorists working across a spectrum from fundamental mathematical theory to LHC phenomenology.
Sectors Digital/Communication/Information Technologies (including Software),Education

Description Knowledge Exchange: Activities covered by the STFC Consolidated grant are closely linked to the formation and execution of Supercomputing Wales, the successor to HPC Wales. Biagio Lucini is Swansea PI of Supercomputing Wales and the lattice QCD group is one of main users of the facility, leveraged by the STFC Consolidated grant as a target towards grant income required by WEFO. On a related basis, Swansea University has recently founded its Swansea Academy for Advanced Computing. SA2C has been set up to further the university research objectives by providing state of the art research computing technology and skills to researchers at Swansea University. With Biagio Lucini as Director, SA2C currently employs 5 research software engineers, three of which are (former) lattice gauge theorists. Public Outreach: Oriel Science is a public outreach project developed under the leadership of Prof Chris Allton. It has established a city-centre location in Swansea and hosts exhibitions based on science research in the University, as well as coordinating an extensive schools science outreach programme. An exhibition "The Story of Time" in 2016 highlighted our STFC funded research on the LHC and quantum aspects of gravity. Prof Allton has since been awarded an STFC Leadership Fellowship in Public Engagement to build on his work as Director of Oriel Science, and the project is supported by a Public Engagement Spark Award.
First Year Of Impact 2016
Sector Digital/Communication/Information Technologies (including Software),Education,Culture, Heritage, Museums and Collections
Impact Types Economic

Description Leverhulme Fellowship
Amount £45,000 (GBP)
Funding ID LT140052 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2015 
End 09/2016
Description UKQCD 
Organisation UKQCD
Country United Kingdom 
Sector Academic/University 
PI Contribution The Swansea Lattice Gauge Theory research group is a member of the UKQCD lattice consortium.
Collaborator Contribution Collaboration on physics content of research papers and use of HPC facilities.
Impact 30 of the refereed publications listed here (authors Aarts, Allton, Hands, Lucini) are in teh field of Lattice Gauge Theory and are related to some extent with UKQCD. The Swansea share of UKQCD's STFC HPC equipment grant procured a £1.2M IBM Blue Gene/P computer located in Swansea. The relation with IBM and software development formed part of the Department's submission in the 2010 REF Impact Pilot exercise.
Description Oriel Science Exhibition Centre 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Prof Chris Allton has led the creation of an Exhibition Centre, named "Oriel Science", in Swansea city centre, presenting the research activity of the University's College of Science to the general public and school visits. The exhibition on "The Story of Time" highlighted research related to the particle theory group's STFC consolidated grant.
Year(s) Of Engagement Activity 2016,2017
Description Particle Physics Masterclasses 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Schools
Results and Impact Approx 120 pupils annually attend two or three separate day-long events featuring lectures and hands-on computer exercises featuring CERN, the LHC, particle physics, ATLAS software and the ALPHA antihydrogen collaboration.

Around 10 schools attend each year. Most have asked to be re-invited on a regular basis to future year's events.
Year(s) Of Engagement Activity 2015
Description Radio Interviews 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Interviews and participation on science programmes for BBC Radio Wales, including Science Cafe programmes on string theory, particle physics and cosmology, the anniversary of Hawking's "Brief History of Time" and the Centenary of Einstein's General Relativity.

Not possible to quantify.
Year(s) Of Engagement Activity 2015