Numerical approaches to Radiative Backreaction in General Relativity

Lead Research Organisation: University of Cambridge
Department Name: Applied Maths and Theoretical Physics

Abstract

This project focuses on numerically solving the nonlinear partial differential equations of general relativity (GR) coupled to non-trivial field theories that exhibit dynamical topological solutions (such as vortex-lines/strings and domain walls). The aim is to calculate the resulting gravitational radiation, as well as the radiative backreaction on these extended objects, using newly developed automatic mesh refinement (AMR) codes. By analogy with electromagnetic waves, the purppose is to advance the mathematical understanding of backreaction processes in GR both numerically and analytically, notably characterising the time evolution of the radiation spectrum. An important component of this project will be collaboration with Intel on the optimization of these AMR GR codes for many-core HPC architectures. The project will also advance high performance data analytics through in-situ (or "on the fly") visualization of the evolving pde solutions. (This represents the development of pioneering collaborative projects being pursued at the DAMTP Intel Parallel Computing Centre, which have been demonstrated at SC'15 and ISC'16.) Note: SC'15 was the Supercomputing 2015 conference in Austin, Texas in November 2015 and ISC'16 the International Supercomputing 2016 conference in Frankfurt this June (the main high performance computing meetings worldwide).

Publications

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Barack L (2019) Black holes, gravitational waves and fundamental physics: a roadmap in Classical and Quantum Gravity

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/P510440/1 01/10/2016 30/09/2021
1783810 Studentship EP/P510440/1 01/10/2016 30/09/2020 Amelia Louise Drew
 
Description The Nobel-Prize-winning detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015 opened up a brand new window into observational cosmology, catalysing research into gravitational wave signatures from a wide range of astrophysical and cosmological sources. For this work, I focus on calculating accurate observational signatures from topological `cosmic' strings which arise if the rapid cooling of the Early Universe triggers a `phase transition', similar to water freezing to ice. Cosmic strings are strongly tied to fundamental physics; detection will enable us to draw deep conclusions about particle physics and the underlying structure of space and time. Accurate signal templates are essential for maximising discovery potential with ongoing LIGO searches as well as the space-based Laser Interferometer Space Antenna (LISA) and the Einstein Telescope.

Further to this, topological strings provide insight into a fundamental question of modern cosmology and particle physics; the identity of dark matter. This is matter that has not been directly observed but has been inferred from astrophysical observations and is predicted to make up around 85% of the total matter in our Universe. Massless 'axion' radiation emitted from `axion strings,' mathematical equivalents of cosmic strings, has been proposed as a dark matter candidate.

Numerical simulations of cosmic strings are significantly computationally challenging; the ratio between the string width and the scale of the Universe is far beyond the capability of current simulations to resolve. My research addresses this using a computational technique called `adaptive mesh refinement' (AMR), which allows the numerical simulation grid to adapt to the scale of the problem. I have performed the first AMR simulations of `global' cosmic strings, exploring and analysing approximately 100 single string simulations using the code GRChombo, for which I am a core developer (http://www.grchombo.org/collaborators). Performing an in-depth analysis of the axion radiation and string evolution, we conclude that the evolution of global strings tends towards the behaviour predicted analytically in the thin-string limit, with radiation damping.
Exploitation Route We have provided a significant step towards accurate prediction of cosmic string signatures using gravitational waves. The outcomes of the project thus far can be used by LIGO (the Laser Interferometer Gravitational-Wave Observatory) and LISA (the Laser Interferometer Space Antenna) Collaborations to aid with understanding these objects.
Sectors Other

 
Description Gonville and Caius Travel Grant
Amount £750 (GBP)
Organisation University of Cambridge 
Department Gonville and Caius College
Sector Academic/University
Country United Kingdom
Start 06/2017 
End 11/2019
 
Description GRChombo 
Organisation Argonne National Laboratory
Country United States 
Sector Public 
PI Contribution Introduction of new features to the GRChombo code and contribution to ongoing discussions on ways to improve code speed and efficiency, including with researchers at Lawrence Berkeley National Laboratory.
Collaborator Contribution Continued development of the GRChombo code including introduction of new features, streamlining the code and keeping the public version up to date, as well as intellectual input into numerical problems. We meet 3 times a year to keep each other updated on the science applications and coding updates, as well as to teach new users.
Impact All simulations in arXiv:1910.01718 were performed using GRChombo, providing quantitative results on the evolution of global cosmic strings.
Start Year 2017
 
Description GRChombo 
Organisation Catholic University of Louvain
Country Belgium 
Sector Academic/University 
PI Contribution Introduction of new features to the GRChombo code and contribution to ongoing discussions on ways to improve code speed and efficiency, including with researchers at Lawrence Berkeley National Laboratory.
Collaborator Contribution Continued development of the GRChombo code including introduction of new features, streamlining the code and keeping the public version up to date, as well as intellectual input into numerical problems. We meet 3 times a year to keep each other updated on the science applications and coding updates, as well as to teach new users.
Impact All simulations in arXiv:1910.01718 were performed using GRChombo, providing quantitative results on the evolution of global cosmic strings.
Start Year 2017
 
Description GRChombo 
Organisation King's College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Introduction of new features to the GRChombo code and contribution to ongoing discussions on ways to improve code speed and efficiency, including with researchers at Lawrence Berkeley National Laboratory.
Collaborator Contribution Continued development of the GRChombo code including introduction of new features, streamlining the code and keeping the public version up to date, as well as intellectual input into numerical problems. We meet 3 times a year to keep each other updated on the science applications and coding updates, as well as to teach new users.
Impact All simulations in arXiv:1910.01718 were performed using GRChombo, providing quantitative results on the evolution of global cosmic strings.
Start Year 2017
 
Description GRChombo 
Organisation Queen Mary University of London
Country United Kingdom 
Sector Academic/University 
PI Contribution Introduction of new features to the GRChombo code and contribution to ongoing discussions on ways to improve code speed and efficiency, including with researchers at Lawrence Berkeley National Laboratory.
Collaborator Contribution Continued development of the GRChombo code including introduction of new features, streamlining the code and keeping the public version up to date, as well as intellectual input into numerical problems. We meet 3 times a year to keep each other updated on the science applications and coding updates, as well as to teach new users.
Impact All simulations in arXiv:1910.01718 were performed using GRChombo, providing quantitative results on the evolution of global cosmic strings.
Start Year 2017
 
Description GRChombo 
Organisation University of Oxford
Country United Kingdom 
Sector Academic/University 
PI Contribution Introduction of new features to the GRChombo code and contribution to ongoing discussions on ways to improve code speed and efficiency, including with researchers at Lawrence Berkeley National Laboratory.
Collaborator Contribution Continued development of the GRChombo code including introduction of new features, streamlining the code and keeping the public version up to date, as well as intellectual input into numerical problems. We meet 3 times a year to keep each other updated on the science applications and coding updates, as well as to teach new users.
Impact All simulations in arXiv:1910.01718 were performed using GRChombo, providing quantitative results on the evolution of global cosmic strings.
Start Year 2017
 
Description Discovery Channel: 'The Universe Unravelled in association with the Stephen Hawking Centre' 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact One-on-one on-camera interviews for a series filmed by the Discovery Channel about cosmology and general relativity. Explained general relativity and cosmic strings in a way that is accessible and informative for a public audience. Will appear in 4 episodes to be aired in 2020, impact to be determined.
Year(s) Of Engagement Activity 2019
 
Description Exhibitioner for HPE at SC18 Conference (supercomputing) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact I was an exhibitioner for HPE using simulations from my research to demonstrate in-situ visualisation with Paraview Catalyst and the Intel Rendering Framework to industry experts.
Year(s) Of Engagement Activity 2018
 
Description Exhibitor at SIGGRAPH 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Exhibitor at SIGGRAPH Conference in Los Angeles, demonstrating the Intel Rendering Framework for Intel's CREATE event.
Year(s) Of Engagement Activity 2019
URL https://newsroom.intel.com/news/siggraph-intels-vision-exascale-class-content-creation-1000x-perform...
 
Description Hewlett Packard Enterprise Promotional Video with Stephen Hawking 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact I gave an interview with HPE on the benefits of in-memory computing to cosmological research. Excerpts from the interview were featured in a promotional video with Stephen Hawking and other members of Centre for Theoretical Cosmology. The video was uploaded onto youtube and was also linked from Stephen Hawking's facebook page (https://www.facebook.com/watch/?v=1606880102732414).
Year(s) Of Engagement Activity 2017
URL https://www.youtube.com/watch?v=MgGhfuxUc44
 
Description Panellist for Gravitational Wave Probes of Fundamental Physics Workshop, Amsterdam 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Invited participation in panel on numerical relativity at workshop "Gravitational Wave Probes of Fundamental Physics" in Amsterdam.
Year(s) Of Engagement Activity 2019
 
Description Talk at BritGrav19, Durham University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact Talk: Radiation from Global Topological Strings using Adaptive Mesh Refinement
Year(s) Of Engagement Activity 2019
 
Description Talk at Cambridge-LMU Cosmology Meeting, LMU (Ludwig-Maximillians-Universitat) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Talk: Axion Strings and Dark Matter
Year(s) Of Engagement Activity 2019
 
Description Talk at Cosmic Topological Defects: Dynamics & Multi-Messenger Signatures Workshop, Leiden 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Talk: Radiation from Global Topological Strings using Adaptive Mesh Refinement
Year(s) Of Engagement Activity 2018
 
Description Talk at Cosmology Journal Club, DAMTP, University of Cambridge 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other audiences
Results and Impact Talk: Radiation from Global Topological Strings using Adaptive Mesh Refinement
Year(s) Of Engagement Activity 2020
 
Description Talk at DAMTP, University of Cambridge, General Relativity Seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other audiences
Results and Impact Talk: Radiation from Global Topological Strings using Adaptive Mesh Refinement
Year(s) Of Engagement Activity 2019
 
Description Talk at Gravitational Wave Proves of Fundamental Physics Workshop, Amsterdam 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Talk: Radiation from Global Topological Strings using Adaptive Mesh Refinement
Year(s) Of Engagement Activity 2019
 
Description Talk at Lawrence Berkeley National Laboratory, Berkeley 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Talk: Radiation from Global Topological Strings using Adaptive Mesh Refinement
Year(s) Of Engagement Activity 2019
 
Description Talk at Numerical Relativity beyond General Relativity Conference, Benasque 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Talk: Observational Signatures from Cosmic and Axion Strings
Year(s) Of Engagement Activity 2018
 
Description Talk at School on Gravitational Waves for Cosmology and Astrophysics, Benasque 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Talk: Primordial Gravitational Wave Signatures from Cosmic Strings
Year(s) Of Engagement Activity 2017
 
Description Women in STEM 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Featured in University of Cambridge #WomenInSTEM campaign, Q&A on University homepage and social media channels.
Year(s) Of Engagement Activity 2019
URL https://www.cam.ac.uk/research/news/women-in-stem-amelia-drew