Integrating out the heaviest quark in N--flavour ChPT

We extend a known method to integrate out the strange quark in three flavour chiral perturbation theory to the context of an arbitrary number of flavours. As an application, we present the explicit formulae to one--loop accuracy for the heavy quark mass dependency of the low energy constants after decreasing the number of flavours by one while integrating out the heaviest quark in N--flavour chiral perturbation theory.Comment: 18 pages, 1 figure. Text and references added. To appear in EPJ

Electromagnetic Transition Form Factors of Mesons

Using a counting scheme which treats pseudoscalar and vector mesons on equal footing, the decays of the narrow light vector mesons omega and phi into a dilepton and a pseudoscalar pi-meson or eta-meson, respectively, are calculated. Thereby, all required parameters could be determined by other reactions so that one has predictive power for the considered decays. The calculated partial decay widths are in very good agreement with the experimental data.Comment: Talk given at the 33rd International School of Nuclear Physics (From Quarks and Gluons to Hadrons and Nuclei) in Erice (Italy

The eta' in baryon chiral perturbation theory

We include in a systematic way the eta' in baryon chiral perturbation theory. The most general relativistic effective Lagrangian describing the interaction of the lowest lying baryon octet with the Goldstone boson octet and the eta' is presented up to linear order in the derivative expansion and its heavy baryon limit is obtained. As explicit examples, we calculate the baryon masses and the pi N sigma-term up to one-loop order in the heavy baryon formulation. A systematic expansion in the meson masses is possible, and appearing divergences are renormalized.Comment: 16 pages, 2 figure

What does a change in the quark condensate say about restoration of chiral symmetry in matter?

The contribution of nucleons to the quark condensate in nuclear matter includes a piece of first order in $m_\pi$, arising from the contribution of low-momentum virtual pions to the $\pi N$ sigma commutator. Chiral symmetry requires that no term of this order appears in the $NN$ interaction. The mass of a nucleon in matter thus cannot depend in any simple way on the quark condensate alone. More generally, pieces of the quark condensate that arise from low-momentum pions should not be associated with partial restoration of chiral symmetry.Comment: 9 pages (RevTeX). Definition of effective mass changed; numerical value of leading nonanalytic term corrected, along with various misprint

Light quarks masses and condensates in QCD

We review some theoretical and phenomenological aspects of the scenario in which the spontaneous breaking of chiral symmetry is not triggered by a formation of a large condensate . Emphasis is put on the resulting pattern of light quark masses, on the constraints arising from QCD sum rules and on forthcoming experimental tests.Comment: 23 pages, 12 Postscript figures, LaTeX, uses svcon2e.sty, to be published in the Proceedings of the Workshop on Chiral Dynamics 1997, Mainz, Germany, Sept. 1-5, 199

Pion Mass Effects in the Large NN Limit of \chiPT

We compute the large $N$ effective action of the $O(N+1)/O(N)$ non-linear sigma model including the effect of the pion mass to order $m^2_{\pi}/f_{\pi}^2$. This action is more complex than the one corresponding to the chiral limit not only because of the pion propagators but also because chiral symmetry produce new interactions proportional to $m^2_{\pi}/f_{\pi}^2$. We renormalize the action by including the appropriate counter terms and find the renormalization group equations for the corresponding couplings. Then we estudy the unitarity propierties of the scattering amplitudes. Finally our results are applied to the particular case of the linear sigma model and also are used to fit the pion scattering phase shifts.Comment: FT/UCM/18/9

Scalar radius of the pion in the Kroll-Lee-Zumino renormalizable theory

The Kroll-Lee-Zumino renormalizable Abelian quantum field theory of pions and a massive rho-meson is used to calculate the scalar radius of the pion at next to leading (one loop) order in perturbation theory. Due to renormalizability, this determination involves no free parameters. The result is $_s = 0.40 {fm}^2$. This value gives for $\bar{\ell}_4$, the low energy constant of chiral perturbation theory, $\bar{\ell}_4 = 3.4$, and $F_\pi/F = 1.05$, where F is the pion decay constant in the chiral limit. Given the level of accuracy in the masses and the $\rho\pi\pi$ coupling, the only sizable uncertainty in this result is due to the (uncalculated) NNLO contribution