Heinrich Leutwyler

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We review lattice results related to pion, kaon, Dand B-meson physics with the aim of making them easily accessible to the particle-physics community. More specifically, we report on the determination of the lightquark masses, the form factor f+(0), arising in semileptonic K → π transition at zero momentum transfer, as well as the decay-constant ratio fK /(More)
The paper collects the various pieces of information concerning the relative size of mu, md and ms. A coherent picture results, which constrains the mass ratios to a rather narrow range: mu/md=0.553± 0.043, ms/md=18.9± 0.8. CERN-TH/96-44 February 1996 Work supported in part by Schweizerischer Nationalfonds 1. I wish to show that recent results of chiral(More)
The properties of the effective field theory relevant for the low energy structure generated by the Goldstone bosons of a spontaneously broken symmetry are reexamined. It is shown that anomaly free, Lorentz invariant theories are characterized by a gauge invariant effective Lagrangian, to all orders of the low energy expansion. The paper includes a(More)
We demonstrate that, together with the available experimental information, chiral symmetry determines the low energy behaviour of the ππ scattering amplitude to within very small uncertainties. In particular, the threshold parameters of the S–, P–, D– and F–waves are predicted, as well as the mass and width of the ρ and of the broad bump in the S–wave. The(More)
Chiral perturbation theory is extended to nonrelativistic systems with spontaneously broken symmetry. In the effective Lagrangian, order parameters associated with the generators of the group manifest themselves as effective coupling constants of a topological term, which is gauge invariant only up to a total derivative. In the case of the ferromagnet, a(More)
The talk reviews the current status of knowledge concerning mu, md and ms. Qualitative aspects of the resulting picture for the breaking of isospin and eightfold way symmetries are discussed. At a more quantitative level, the review focuses on the chiral perturbation theory results for the masses of the Goldstone bosons. The corresponding bounds and(More)
Recent work in light flavour hadron physics is reviewed. In particular, I discuss the significance of the progress achieved with light dynamical quarks on the lattice for the effective low energy theory of QCD. Also, I draw attention to some puzzling results from NA48 and KTeV concerning the scalar form factor relevant for Kμ3 decay – taken at face value,(More)
In the large Nc limit, the variables required to analyze the low energy structure of QCD in the framework of an effective field theory necessarily include the degrees of freedom of the η. We evaluate the decay constants of the pseudoscalar nonet to one loop within this extended framework and show that, as a consequence of the anomalous dimension of the(More)