17 research outputs found
Electromagnetic finite-size effects to the hadronic vacuum polarization
In order to reduce the current hadronic uncertainties in the theory
prediction for the anomalous magnetic moment of the muon, lattice calculations
need to reach sub-percent accuracy on the hadronic-vacuum-polarization
contribution. This requires the inclusion of
electromagnetic corrections. The inclusion of electromagnetic interactions in
lattice simulations is known to generate potentially large finite-size effects
suppressed only by powers of the inverse spatial extent. In this paper we
derive an analytic expression for the finite-volume
corrections to the two-pion contribution to the hadronic vacuum polarization at
next-to-leading order in the electromagnetic coupling in scalar QED. The
leading term is found to be of order where is the spatial extent.
A term is absent since the current is neutral and a photon far away
thus sees no charge and we show that this result is universal. Our analytical
results agree with results from the numerical evaluation of loop integrals as
well as simulations of lattice scalar gauge theory with stochastically
generated photon fields. In the latter case the agreement is up to
exponentially suppressed finite-volume effects. For completeness we also
calculate the hadronic vacuum polarization in infinite volume using a basis of
2-loop master integrals.Comment: 42 pages, 11 figure
Isospin-breaking corrections to light leptonic decays in lattice QCD+QED at the physical point
We report on the physical-point RBC/UKQCD calculation of the leading
isospin-breaking corrections to light-meson leptonic decays. This is highly
relevant for future precision tests in the flavour physics sector, in
particular the first-row unitarity of the Cabibbo-Kobayashi-Maskawa matrix
containing the elements and . The simulations were performed
using Domain-Wall fermions for flavours, and with isospin-breaking
effects included perturbatively in the path integral through order and
. We use QED for the
inclusion of electromagnetism, and discuss here the non-locality of this
prescription which has significant impact on the infinite-volume extrapolation.Comment: Proceedings for The 39th International Symposium on Lattice Field
Theory, 8th-13th August, 2022, Rheinische Friedrich-Wilhelms-Universit\"at
Bonn, Bonn, German
Workshop summary:Kaons@CERN 2023
Kaon physics is at a turning point â while the rare-kaon experiments NA62 and KOTO are in full swing, the end of their lifetime is approaching and the future experimental landscape needs to be defined. With HIKE, KOTO-II and LHCb-Phase-II on the table and under scrutiny, it is a very good moment in time to take stock and contemplate about the opportunities these experiments and theoretical developments provide for particle physics in the coming decade and beyond. This paper provides a compact summary of talks and discussions from the Kaons@CERN 2023 workshop, held in September 2023 at CERN
Workshop summary -- Kaons@CERN 2023
Kaon physics is at a turning point -- while the rare-kaon experiments NA62
and KOTO are in full swing, the end of their lifetime is approaching and the
future experimental landscape needs to be defined. With HIKE, KOTO-II and
LHCb-Phase-II on the table and under scrutiny, it is a very good moment in time
to take stock and contemplate about the opportunities these experiments and
theoretical developments provide for particle physics in the coming decade and
beyond. This paper provides a compact summary of talks and discussions from the
Kaons@CERN 2023 workshop.Comment: 54 pages, Summary of Kaons@CERN 23 workshop, references and
clarifications adde
The anomalous magnetic moment of the muon in the Standard Model
194 pages, 103 figures, bib files for the citation references are available from: https://muon-gm2-theory.illinois.eduWe review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant and is broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including with negligible numerical uncertainty. The electroweak contribution is suppressed by and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at and is due to hadronic vacuum polarization, whereas at the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first-principle, lattice-QCD approach. The final result reads and is smaller than the Brookhaven measurement by 3.7. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. This and the prospects to further reduce the theoretical uncertainty in the near future-which are also discussed here-make this quantity one of the most promising places to look for evidence of new physics
The anomalous magnetic moment of the muon in the Standard Model
We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant α and is broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including O(α5) with negligible numerical uncertainty. The electroweak contribution is suppressed by (mÎŒâMW)2 and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at O(α2) and is due to hadronic vacuum polarization, whereas at O(α3) the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first-principle, lattice-QCD approach. The final result reads aÎŒSM=116591810(43)Ă10â11 and is smaller than the Brookhaven measurement by 3.7Ï. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. This and the prospects to further reduce the theoretical uncertainty in the near future â which are also discussed here â make this quantity one of the most promising places to look for evidence of new physics
Prospects for precise predictions of aΌ in the Standard Model
We discuss the prospects for improving the precision on the hadronic corrections to the anomalous magnetic moment of the muon, and the plans of the Muon gâ2 Theory Initiative to update the Standard Model prediction
Workshop summary: Kaons@CERN 2023
Kaon physics is at a turning point â while the rare-kaon experiments NA62 and KOTO are in full swing, the end of their lifetime is approaching and the future experimental landscape needs to be defined. With HIKE, KOTO-II and LHCb-Phase-II on the table and under scrutiny, it is a very good moment in time to take stock and contemplate about the opportunities these experiments and theoretical developments provide for particle physics in the coming decade and beyond. This paper provides a compact summary of talks and discussions from the Kaons@CERN 2023 workshop, held in September 2023 at CERN
Report on the ECFA Early-Career Researchers Debate on the 2020 European Strategy Update for Particle Physics
A group of Early-Career Researchers (ECRs) has been given a mandate from the European Committee for Future Accelerators (ECFA) to debate the topics of the current European Strategy Update (ESU) for Particle Physics and to summarise the outcome in a brief document [1]. A full-day debate with 180 delegates was held at CERN, followed by a survey collecting quantitative input. During the debate, the ECRs discussed future colliders in terms of the physics prospects, their implications for accelerator and detector technology as well as computing and software. The discussion was organised into several topic areas. From these areas two common themes were particularly highlighted by the ECRs: sociological and human aspects; and issues of the environmental impact and sustainability of our research
Workshop summary -- Kaons@CERN 2023
International audienceKaon physics is at a turning point -- while the rare-kaon experiments NA62 and KOTO are in full swing, the end of their lifetime is approaching and the future experimental landscape needs to be defined. With HIKE, KOTO-II and LHCb-Phase-II on the table and under scrutiny, it is a very good moment in time to take stock and contemplate about the opportunities these experiments and theoretical developments provide for particle physics in the coming decade and beyond. This paper provides a compact summary of talks and discussions from the Kaons@CERN 2023 workshop