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.
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.