Periodic Reporting for period 4 - NewPhysLat (Search for new physics through lattice simulations)
Reporting period: 2022-04-01 to 2023-09-30
This project focuses on high-precision simulations based on lattice field theory to predict theoretical fundamental physics quantities currently investigated in international experimental programmes. Each project presented here is pushing the boundaries of the current knowledge and possibilities in the applications of lattice field theory and will have significant consequences on the theoretical understanding of strongly coupled field theories. Two of the research projects presented below focus on the Standard Model of particle physics through rare kaon decays (project RK) and the inclusion of isospin-breaking effects in lattice simulations (Project IB). The quantities studied in this project are directly related to the CERN (NA62 and LHCb experiment) programme, the g-2 experiment in Fermilab (USA), and, generally, flavour physics experiments worldwide. The third project focuses on more general lattice field theories and holographic cosmology (Project HC). This project aims to uncover new theoretical insights into the laws of physics in the very early Universe by constraining holographic models using data from the Planck satellite. Finally, all the projects will strongly support the development of Grid and Hadrons, one of the leading next-generation lattice simulation software, described as Project G.
The general problem this project addresses is the search for new subatomic particles or fundamental interactions and the search for new fundamental laws of physics applicable to the very early Universe. This project addresses these issues by providing reliable high-precision predictions through ab initio simulations that can be directly compared with experimental measurements. Another methodological problem this project addresses is the development of a unified open-source software suite that can perform such simulations on exascale supercomputer systems. These tools can be used on various problems beyond the specific calculations performed in this project, including in data science, artificial intelligence and engineering.
The general problem this project addresses is the search for new subatomic particles or fundamental interactions and the search for new fundamental laws of physics applicable to the very early Universe. This project addresses these issues by providing reliable high-precision predictions through ab initio simulations that can be directly compared with experimental measurements. Another methodological problem this project addresses is the development of a unified open-source software suite that can perform such simulations on exascale supercomputer systems. These tools can be used on various problems beyond the specific calculations performed in this project, including in data science, artificial intelligence and engineering.
1) Project IB (Isospin-breaking effects)
The first step of this project was to include electromagnetic corrections in lattice calculations of the hadronic vacuum polarisation, a crucial contribution to the anomalous magnetic moment of the muon (g-2). The project delivered the first proof-of-concept calculation [1] of these effects, the first theoretical estimation of electromagnetic finite-size effects [2], and the first realistic calculation of the muon g-2 which includes these effects [3]. The project then focused on generalising the theoretical formalism for electromagnetic finite-size effects introduced in [4] to include effects from hadronic structures fully. The main aim was to compute higher-order finite-size effects for radiative corrections to leptonic decays, which was achieved in [5] and revealed a more challenging structure than previously known in the literature. In parallel, a 5-years effort led to the first lattice calculation of these corrections using physical-point lattice simulations [6]. Our result agrees with a previous determination by the RM123S Collaboration, which was extrapolated from simulations at non-physical masses.
2) Project RK (Rare kaon decays)
The first calculation of the rare kaon decay K+ to pi+l+l- was published in [7]. This work represents a substantial 5-year technical effort, and despite the investment of considerable computational resources in the calculation, it did not lead to a statistically resolved result. However, this result allowed us to understand precisely this new challenge and potentially how to resolve it, and this observation could only have been done with a realistic calculation of this grade. During the project, members of the phenomenology community and the LHCb experiment prompted us several times about a potential generalisation of our methodology to hyperons decays. Therefore, we started a theoretical project on rare Sigma decays, which was published in [8]. A numerical proof-of-concept calculation was done, which we expect will lead to a publication in the short term.
3) Project HC (Holographic cosmology)
This subproject was the highest risk component of the grant. We managed to solve critical problems, enabling the use of lattice simulation to constrain holographic cosmological models. One of the most significant issues in current work in holographic cosmology is the use of perturbation theory, which is affected by severe infrared divergence problems. We confirmed in [9] that, as conjectured in 1981 by Jackiw and Templeton, these divergences are an artefact of perturbation theory. We also solved how to renormalise the EMT in scalar theories [10], a vital issue of the lattice methodology. Research on that topic will continue, and couple to research in cosmology in the next couple of years.
4) Project G (Development of the Grid library)
Grid & Hadrons are now well-established, exascale-ready open-source lattice software. The contribution of this project was significant, as both frameworks were expanded and used to implement all work packages. The Grid software was used to procure the two phases of the £14M national supercomputer Tursa in the UK. Approximately two-thirds of the computing resources on Tursa were used to support this project. This had a considerable influence on the shaping of the service and drove innovation, for example, around optimising the energy efficiency of lattice simulations [11], leading to an estimated 100 MWh of energy saving using Tursa.
[1]: https://doi.org/10.1007/JHEP09(2017)153(opens in new window)
[2]: https://doi.org/10.1103/PhysRevD.100.014508(opens in new window)
[3]: https://doi.org/10.1103/PhysRevLett.121.022003(opens in new window)
[4]: https://doi.org/10.1103/PhysRevD.99.03451(opens in new window)
[5]: https://doi.org/10.1103/PhysRevD.105.074509(opens in new window)
[6]: https://doi.org/10.1007/JHEP02(2023)242(opens in new window)
[7]: https://doi.org/10.1103/PhysRevD.107.L011503(opens in new window)
[8]: https://doi.org/10.1007/JHEP04(2023)108(opens in new window)
[9]: https://doi.org/10.1103/PhysRevLett.126.221601(opens in new window)
[10]: https://doi.org/10.1103/PhysRevD.103.114501(opens in new window)
[11]:https://zenodo.org/records/7057319
The first step of this project was to include electromagnetic corrections in lattice calculations of the hadronic vacuum polarisation, a crucial contribution to the anomalous magnetic moment of the muon (g-2). The project delivered the first proof-of-concept calculation [1] of these effects, the first theoretical estimation of electromagnetic finite-size effects [2], and the first realistic calculation of the muon g-2 which includes these effects [3]. The project then focused on generalising the theoretical formalism for electromagnetic finite-size effects introduced in [4] to include effects from hadronic structures fully. The main aim was to compute higher-order finite-size effects for radiative corrections to leptonic decays, which was achieved in [5] and revealed a more challenging structure than previously known in the literature. In parallel, a 5-years effort led to the first lattice calculation of these corrections using physical-point lattice simulations [6]. Our result agrees with a previous determination by the RM123S Collaboration, which was extrapolated from simulations at non-physical masses.
2) Project RK (Rare kaon decays)
The first calculation of the rare kaon decay K+ to pi+l+l- was published in [7]. This work represents a substantial 5-year technical effort, and despite the investment of considerable computational resources in the calculation, it did not lead to a statistically resolved result. However, this result allowed us to understand precisely this new challenge and potentially how to resolve it, and this observation could only have been done with a realistic calculation of this grade. During the project, members of the phenomenology community and the LHCb experiment prompted us several times about a potential generalisation of our methodology to hyperons decays. Therefore, we started a theoretical project on rare Sigma decays, which was published in [8]. A numerical proof-of-concept calculation was done, which we expect will lead to a publication in the short term.
3) Project HC (Holographic cosmology)
This subproject was the highest risk component of the grant. We managed to solve critical problems, enabling the use of lattice simulation to constrain holographic cosmological models. One of the most significant issues in current work in holographic cosmology is the use of perturbation theory, which is affected by severe infrared divergence problems. We confirmed in [9] that, as conjectured in 1981 by Jackiw and Templeton, these divergences are an artefact of perturbation theory. We also solved how to renormalise the EMT in scalar theories [10], a vital issue of the lattice methodology. Research on that topic will continue, and couple to research in cosmology in the next couple of years.
4) Project G (Development of the Grid library)
Grid & Hadrons are now well-established, exascale-ready open-source lattice software. The contribution of this project was significant, as both frameworks were expanded and used to implement all work packages. The Grid software was used to procure the two phases of the £14M national supercomputer Tursa in the UK. Approximately two-thirds of the computing resources on Tursa were used to support this project. This had a considerable influence on the shaping of the service and drove innovation, for example, around optimising the energy efficiency of lattice simulations [11], leading to an estimated 100 MWh of energy saving using Tursa.
[1]: https://doi.org/10.1007/JHEP09(2017)153(opens in new window)
[2]: https://doi.org/10.1103/PhysRevD.100.014508(opens in new window)
[3]: https://doi.org/10.1103/PhysRevLett.121.022003(opens in new window)
[4]: https://doi.org/10.1103/PhysRevD.99.03451(opens in new window)
[5]: https://doi.org/10.1103/PhysRevD.105.074509(opens in new window)
[6]: https://doi.org/10.1007/JHEP02(2023)242(opens in new window)
[7]: https://doi.org/10.1103/PhysRevD.107.L011503(opens in new window)
[8]: https://doi.org/10.1007/JHEP04(2023)108(opens in new window)
[9]: https://doi.org/10.1103/PhysRevLett.126.221601(opens in new window)
[10]: https://doi.org/10.1103/PhysRevD.103.114501(opens in new window)
[11]:https://zenodo.org/records/7057319
1) Project IB (Isospin-breaking effects)
- the first calculation of the hadronic vacuum polarisation, including electromagnetic corrections [1,3];
- a model-independent and relativistic theoretical formalism for electromagnetic finite-size effects [2,4,5];
- the first calculation of the radiative corrections to pion and kaon leptonic decay directly using physical point lattice simulations [6].
2) Project RK (Rare kaon decays)
- the first calculation of the rare kaon decay K+ to pi+l+l- amplitude using physical point simulations [7];
- the first theoretical formalism for rare hyperon decays Sigma+ to pl+l- [8].
3) Project HC (Holographic cosmology)
- the numerical demonstration of a 40-year-old conjecture on the infrared-finiteness of three-dimensional massless scalar field theories [9];
- a methodology based on the Wilson flow to renormalise the lattice energy-momentum tensor (EMT) [10].
4) Project G (Development of the Grid library)
- development of the Grid library (https://github.com/paboyle/Grid/)(opens in new window);
- emergence and development of the Hadrons software (https://github.com/aportelli/Hadrons(opens in new window)) a workflow management system based on Grid;
- optimisation of the energy efficiency of lattice simulations on the UK national service Tursa [11].
- the first calculation of the hadronic vacuum polarisation, including electromagnetic corrections [1,3];
- a model-independent and relativistic theoretical formalism for electromagnetic finite-size effects [2,4,5];
- the first calculation of the radiative corrections to pion and kaon leptonic decay directly using physical point lattice simulations [6].
2) Project RK (Rare kaon decays)
- the first calculation of the rare kaon decay K+ to pi+l+l- amplitude using physical point simulations [7];
- the first theoretical formalism for rare hyperon decays Sigma+ to pl+l- [8].
3) Project HC (Holographic cosmology)
- the numerical demonstration of a 40-year-old conjecture on the infrared-finiteness of three-dimensional massless scalar field theories [9];
- a methodology based on the Wilson flow to renormalise the lattice energy-momentum tensor (EMT) [10].
4) Project G (Development of the Grid library)
- development of the Grid library (https://github.com/paboyle/Grid/)(opens in new window);
- emergence and development of the Hadrons software (https://github.com/aportelli/Hadrons(opens in new window)) a workflow management system based on Grid;
- optimisation of the energy efficiency of lattice simulations on the UK national service Tursa [11].