Gauge Theories and Strings in the LHC Era

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

Abstract

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 group is 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 group 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. The quantum fluctuations of this field would show up at the LHC as the famous Higgs boson. 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, as described by a class of theories known in analogy with QCD as `technicolor'. Again, we are studying these theories 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. 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 group's activities in the areas of Knowledge Exchange and Outreach. Knowledge Exchange is centred on the Lattice group's exploitation of HPC facilities, especially through the close involvement of the UKQCD collaboration with IBM and the development of the Blue Gene series of machines. The Swansea group has established a close contact with IBM Research at Yorktown Heights, running lattice code as a test application to evaluate computer performance and development. The group is also active in developing Grid technology. Outreach activities are focused in three areas - schools activities, popular lectures and media involvement. The group organises two activities for schools: Particle Physics Masterclasses with hands-on computer sessions using ATLAS software to analyse LHC events for 6th form students and annual Christmas Lectures for younger pupils. Group members give frequent public lectures, especially to local astronomy societies and science cafes. We have also exploited the publicity surrounding the start-up of the LHC, as well as the success of the Department's atomic physics group in the creation and trapping of atoms of antimatter at CERN, through a series of TV and Radio appearances as well as newspaper and magazine articles

Publications

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Zacarías S (2014) Semiclassical strings and non-Abelian T-duality in Physics Letters B

 
Description Significant progress was made in each of the three main research areas followed during the course of this grant - Gauge Theories and Strings, Amplitudes, and Lattice Gauge Theory. Specific key findings in each area included the following.

Gauge Theories and Strings:

Extensive investigations of the quantisation of string theory on AdS x S spacetimes exploiting the key underlying concept of integrability have revealed that the AdS/CFT correspondence,
or gauge-gravity duality, may be extended to a wider class of theories beyond the strong and weak coupling limits.

The scope of gauge-gravity duality was further extended in many areas, notably the holographic description of theories with minimal supersymmetry and in the construction of Type IIB string backgrounds dual to a high density state of deconfined quark matter.

The first complete calculation was made of glueballs in a top-down construction of the gauge-gravity dual to a strongly coupled theory which exhibits a parametrically light composite scalar. This resonates with a phenomenological analysis of LHC data showing that the recently discovered 125 GeV Higgs boson is compatible with an interpretation as a holograhic techni-dilaton.

The discovery of novel analytic structures of Green functions induced by the geometry of null geodesic congruences led to the reformulation of the optical theorem in curved spacetime together with a clear understanding of the effect of gravitational tidal forces on the virtual screening cloud surrounding propagating quantum fields.

Amplitudes:

Substantial progress was made towards understanding the possible perturbative finiteness of N=8 supergravity, notably the prediction that 3-loop divergences in N=4 would cancel, which was subsequently confirmed by explicit calculations.

Lattice Gauge Theory:

Detailed analytical and numerical studies resulted in an improved understanding of the applicability of complex Langevin dynamics to theories such as QCD with a `sign problem' in the presence of a non-zero chemical potential.

The first lattice QCD studies were carried out of the dynamics of bottomonium in the quark-gluon plasma using non-relativistic QCD, with results in agreement with those of the CMS collaboration at the LHC, in particular the survival of the Upsilon ground state and suppression of the excited states.

The first exploration of the phase diagram in the temperature/baryochemical potential plane via full simulation
of a gauge theory showed that quark matter may remain confined over a wide range of density.

The centre-vortex description of confinement in gauge theories was further developed and extended to SU(3)
using an improved lattice algorithm for vortex identification.

The first non-supersymmetric strongly coupled theory known to display infrared conformal behaviour, viz. the SU(2) gauge theory with two adjoint Dirac fermions, was identified and investigated.

Lattice calculations of the glueball spectrum were able for the first time to discriminate single-particle states from scattering states, in full QCD and in SU(N) Yang-Mills theory at large N.
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: High Performance Computing. Research in HPC benefits from interactions with scientists working in lattice gauge theories, since this field naturally provides applications that stress machines to their limits. The Swansea group has developed close links with IBM Research Watson Labs in New York. As part of this collaboration, we have enjoyed early access to the newest supercomputer architectures while providing IBM with our state-of-the-art research codes for testing their machines. In the course of the collaboration with IBM, a benchmark suite was extracted from the research code developed by the lattice gauge theory group to study strongly-coupled beyond the standard model (BSM) dynamics. This tool, called BSMBench, is now released as a collaborative open source project and is hosted at www.bsmbench.org. The unique characteristic of this software is the possibility to change with fine resolution the relative importance of computations and communications, which is the single most influential factor in HPC computations. A third party company, BSMBench Ltd, has been formed with the mission to develop and promote BSMBench. The lattice strong dynamics subgroup is committed to collaborate with BSMBench Ltd in order to improve the code (e.g. by porting it to GPU systems) and to promote its usage on a wide variety of HPC architectures.
First Year Of Impact 2013
Sector Digital/Communication/Information Technologies (including Software)
Impact Types Economic

 
Description Leverhulme Fellowships (2)
Amount £70,000 (GBP)
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 10/2013 
End 09/2016
 
Description STFC Standard Grant
Amount £1,203,993 (GBP)
Funding ID ST/H008829/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 11/2009 
End 10/2012
 
Description University Research Fellowship
Amount £329,843 (GBP)
Funding ID UF090003 
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 10/2010 
End 09/2013
 
Description Wolfson Research Merit Awards (2)
Amount £100,000 (GBP)
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 10/2013 
End 09/2019
 
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 Newspaper articles 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Many newspaper and magazine articles featuring research at CERN, especially antihydrogen.

Not possible to quantify.
Year(s) Of Engagement Activity 2015
 
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 Popular lectures 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Swansea Theoretical Particle Physics Group members give numerous popular talks to the general public and school,
nationally and internationally. Examples include talks on the LHC, CERN AntimatterPhysics and the Einstein Centenary
at the Swansea Science Cafe and Black Holes at local astronomical societies.


Popular interest in lectures and requests for follow-up activity, e.g. interviews for local media.
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