LATTICE QCD · testing the standard model of elementary particles from first principles computations
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2005-09-01 → 2007-08-31
- EU contribution
- €129,643
- Participants
- 1
- Scheme
- EIF
Lines connect the coordinator with its partners.
Results in brief
Final Activity Report Summary - LATTICE QCD (Lattice QCD: testing the Standard Model of elementary particles from first principles computations)
The goal of this project was to contribute to the progress of knowledge in the interactions of the elementary particles and more precisely of those carrying the colour charge. The theory that describes the chromodynamic interaction is called QCD and has been validated over many years by a large amount of experimental tests. In spite of this big success, the theory has not been solved analytically and as a result the quantitative prediction from first principles of much of its rich low-energy phenomenology remains a big challenge. The interactions of light hadrons at low momenta are determined to a large extent by the pattern of spontaneous chiral symmetry breaking, since the light hadrons are the Nambu-Goldstone bosons of this breaking. Those interactions can be described by a chiral effective theory, which encodes chiral symmetry and its spontaneous breaking, and parametrises the rest in terms of so-called low energy couplings (LECs). These couplings must be ideally determined non-perturbatively, and lattice QCD constitutes a very powerful tool in this sense. Matching lattice QCD results with the chiral effective theory allows to extract the LECs in a model-independent way: once they are known, the effective theory becomes a predictive framework for investigating low-energy properties of strong interactions. The project investigated this topic in several aspects: (i) we performed a systematic matching of quenched chiral effective theory at leading order with quenched QCD: here we verified that the leading order behaviour predicted by the quenched chiral effective theory is well reproduced by the lattice data. We performed the matching in two different kinematical corners of the chiral regime, namely the 'p' and the 'epsilon' regimes, showing that the LECs obtained in the two cases are in agreement. (ii) We analysed how spontaneous breaking of chiral symmetry at non-zero lattice spacing could affect the LECs obtained on the lattice. (iii) We investigated finite-volume effects in heavy-light mesons made out of a heavy quark (charm or bottom) and a light one (up, down or strange) by using the ordinary chiral effective theory and the so-called heavy meson chiral perturbation theory. (iv) We started a lattice feasibility study with Wilson sea quarks and Ginsparg-Wilson valence quarks, with the aim of matching the lattice results with the predictions of the chiral effective theory and extract the corresponding couplings. These achievements contribute to the understanding of the structure of QCD at low energy and more generally to the testing of the Standard Model of fundamental interactions.
Data: CORDIS, © European Union
Project objective
The Standard Model of elementary particles is up to now the accepted framework describing electromagnetic, weak and strong interactions. In particular, Quantum Chromodynamics (QCD) successfully describes strong interactions. Nevertheless, relevant issues are still open and the quantitative predictions from first principles remain a big challenge, mainly due to the non-perturbative nature of many processes involved in strong interactions.By formulating QCD on a dicretised space-time (lattice) one obtains an important tool to investigate non-perturbative phenomena and to compute the fundamental parameters of the Standard Model in a model-independent way and with a full control on the systematic errors. In particular, this project will focuse on the non-leptonic kaon decays; by considering the transition amplitude of a kaon in a final state with two pions, one observes empirically that the amplitude for a final state with isospin I=0 is considerably enhanced with respect to the case with isospin I=2 (A0/A2=22.1).This is known as AI=1-2 rule, and the understanding of the underlying mechanism will be the main purpose of the project. This goal will be pursued by determining though lattice QCD computations the low-energy coupling constants of Chiral Perturbation Theory that are directly connected to QCD contributions to the AI=1/2 rule. The key ingredient will be the use of Ginsparg-Wilson fermions; in this formulation, the chiral symmetry is preserved at non-zero lattice spacing and this simplifies considerably the renormalisation of the operators.The relevant three-point functions will be computed through a numerical Monte Carlo simulation. The physical parameters will be extracted by using recent analytic developments on Chiral Perturbation Theory at finite volume (epsilon expansion). A first principle computation of the AI=1/2 rule is still missing and hence the outcome of the project will be an important step in testing the Standard Model.
Original text from CORDIS.
Participants
- UNIVERSITAT DE VALENCIA · BURJASOTCoordinatorSpain
Links
Data: CORDIS, © European Union