# Matter in Extreme Conditions

Lead Research Organisation:
University of Plymouth

Department Name: Sch of Computing & Mathematics

### Abstract

QCD is the quantum theory of the strong interaction, formulated in terms of elementary entities called quarks and gluons. In a laboratory, however, we only observe composite objects such as protons (qqq) or pi-mesons ( q -- anti-q), collectively known as hadrons. Explaining this dichotomy in a satisfactory way is a major unresolved question in theoretical physics, and indeed commands a prize of 1 million dollars from the Clay Mathematics Institute. In the interim, many important QCD questions can be addressed using a controlled approximation called lattice gauge theory, in which quarks and gluons are formulated only on the discrete points and links of a spacetime lattice. Properties such as the masses and interactions of hadrons, and the nature of the gluonic flux tube which holds quarks together with a force sufficient to lift 3 elephants can then be calculated using a numerical technique called Monte Carlo Importance Sampling. Precise lattice QCD results are now a crucial ingredient in projects which, by comparing theoretical predictions with the results of collider experiments, aim both to determine parameters of the Standard Model of particle physics, and if inconsistencies are found, to open up the exciting prospect of 'new physics'. Unfortunately, the number of lattice points required to make the calculations with the necessary precision is large, as is the computational effort associated with intermediate steps of the calculation once the quarks are assigned realistically small masses. In this proposal we argue that in order to achieve the required accuracy state-of-the-art high performance computing resources are needed; indeed, we cost our bid in units of 'teraflop-years', equivalent to some 3x10^19 individual computer operations. Lattice QCD is truly a Grand Challenge. The projects presented in this bid cover a broad sweep of different physics, ranging from precision calculations of hadrons; the properties of systems including heavy quarks such as 'charm' and 'bottom'; extracting fundamental parameters of the Standard Model of Particle Physics (such as the masses and decay properties of hadrons); the quark-gluon plasma which forms at temperatures in excess of a trillion kelvin; the exotic 'quark matter' thought to exist in the cores of neutron stars (having the mass of the Sun but compact enough to comfortably fit in Swansea Bay!); finally, the properties of QCD-like models in which the numbers of quarks and gluons differs from their real- world values of 3 and 8, offering the tantalising promise of making contact with pencil-and-paper approaches and ultimately the Clay prize....

### Publications

Bowman P
(2011)

*Role of center vortices in chiral symmetry breaking in SU(3) gauge theory*in Physical Review D
Del Debbio L
(2010)

*Higher representations on the lattice: Numerical simulations, SU(2) with adjoint fermions*in Physical Review D
Dunne G
(2009)

*Worldline Monte Carlo for fermion models at large N f*in Journal of High Energy Physics
Greensite J
(2013)

*Effective Polyakov line action from strong lattice couplings to the deconfinement transition*in Physical Review D
Greensite J
(2013)

*Effective Polyakov line action from the relative weights method*in Physical Review D
Langfeld K
(2010)

*Confinement and the quark Fermi surface in SU ( 2 N ) QCD-like theories*in Physical Review D
Langfeld K
(2011)

*Confinement from semiclassical gluon fields in gauge theory*in Nuclear Physics B
Langfeld K
(2013)

*Phase diagram of the quantum O ( 2 ) model in 2 + 1 dimensions*in Physical Review D
Langfeld K
(2011)

*Yang-Mills streamlines and semi-classical confinement*
Langfeld K
(2013)

*Two-color QCD with heavy quarks at finite densities*in Physical Review DDescription | The research has addressed one of the outstanding issues in particle physics: the properties of matter at low temperatures and finite densities. Lattice gauge theories have been for many decades providing first principle results from the QCD, the theory of strong interactions. Since standard Monte-Carlo simulations of the these theories are impossible at finite densities due to the notorious sign problem, other approaches must come into play. We were abel to address this issue: - by deriving an effective theory for the Polykov line that can be generalised to finite densities in an exact way. It is expected that the simulation of this theory should be less afflicted by the sign problem. - by revealing effective degrees of freedom, the streamline configurations, that are linked to the property of colour confinement. At 2-5 nuclear matter densities, QCD is believed to udnergo a de-confinement transition. Hence, streamkine configuations are expected to paly a major role at these densities. - by developping a new powerfull approach, the density-of-states method, which might provide a generic and practical solution of the sign problems at densities taht are highly rekevant for phenomenology (e.g. physics of compact stars). This has led to further developments (see below). |

Exploitation Route | The density-of-states method has already been generalised and successfully applied to address Quantum Fields Theories with a sign problem. This follow-up research is funded by STFC under "New Ideas fro Gauge Fields and Strings" (ST/L000350/1). |

Sectors | Digital/Communication/Information Technologies (including Software),Education,Other |

Description | The award made it possible to install a tightly coupled HPC facility at Plymouth University (DiRAC framework). The installation became part of a HPC centre with additional hardware, funded by the Fcaulty and other fundin bodies, and, amog others, supporting rsearch in teh Marine Sciences. After the end of the award, the cluster is still maintained by the University. It still underpins Particle Physics research, helps to train stundents and professional in HPC adminsitartion and OS and facilitates student training at all levels in HPC simulations. |

First Year Of Impact | 2011 |

Sector | Education |

Impact Types | Societal,Policy & public services |

Description | Laser_umea |

Organisation | Umea University |

Department | Department ofÂ Physics |

Country | Sweden |

Sector | Academic/University |

PI Contribution | Scientific collaboration, discussions, publications |

Collaborator Contribution | scientific collaboration, publications |

Impact | Publications, visits |

Start Year | 2009 |

Description | QFT_Jena |

Organisation | Friedrich Schiller University Jena (FSU) |

Department | Theoretical - Institute of Physics |

Country | Germany |

Sector | Academic/University |

PI Contribution | discussions, seminars |

Collaborator Contribution | Scientific collaboration; |

Impact | two publications in peer reviewed journals |

Start Year | 2008 |

Description | HPC_Teach |

Form Of Engagement Activity | Participation in an activity, workshop or similar |

Part Of Official Scheme? | No |

Geographic Reach | Local |

Primary Audience | Professional Practitioners |

Results and Impact | Undergraduate and PhD HPC training, dissemination of HPC skills across research groups of the Faculty. dissemination of HPC skills |

Year(s) Of Engagement Activity | 2010,2011,2012,2013,2014,2015,2016 |