The eta' and the topological charge density

We compare two different frameworks which have been proposed to include the eta' in chiral perturbation theory. The equivalence of these two approaches is shown both for the purely mesonic case and in the presence of the ground state baryon octet. The relation between the different sets of parameters in both Lagrangians is clarified.Comment: 11 page

Chiral Lagrangians for Baryons coupled to massive Spin-1 Fields

We analyze the effective low--energy field theory of Goldstone bosons and baryons chirally coupled to massive spin--1 fields. We use the electromagnetic baryon form factors to demonstrate the formal equivalence between the vector and the tensor field formulation for the spin--1 fields. We also discuss the origin of the so--called Weinberg term in pion--nucleon scattering and the role of $\rho$--meson exchange. Chirally coupled vector mesons do not give rise to this two--pion nucleon seagull interaction but rather to higher order corrections. Some problems of the formal equivalence arising in higher orders and related to loops are touched upon.Comment: 26 pp, LaTeX, uses epsf and elsart12.sty, 3 figures in separate self-unpacking fil

Can one see the number of colors in eta, eta-prime --> pi^+ pi^- gamma?

We investigate the decays eta, eta-prime --> pi^+ pi^- gamma up to next-to-leading order in the framework of the combined 1/N_c and chiral expansions. Counter terms of unnatural parity at next-to-leading order with unknown couplings are important to acommodate the results both to the experimental decay width and the photon spectrum. The presence of these coefficients does not allow for a determination of the number of colors from these decays.Comment: 8 pages, 2 figure

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

Renormalization of two-loop diagrams in scalar lattice field theory

We present a method to calculate to very high precision the coefficients of the divergences occuring in two-loop diagrams for a massive scalar field on the lattice. The approach is based on coordinate space techniques and extensive use of the precisely known Green's function.Comment: 22 pages, 2 figures, additional results include

Weak hyperon decays in heavy baryon chiral perturbation theory: Renormalization and applications

The complete renormalization of the weak Lagrangian to chiral order q^2 in heavy baryon chiral perturbation theory is performed using heat kernel techniques. The results are compared with divergences appearing in the calculation of Feynman graphs for the nonleptonic hyperon decay Lambda -> p pi^- and an estimate for the size of the counterterm contributions to the s-wave amplitudes in nonleptonic hyperon decays is given.Comment: 21 pages, 2 figure

Comment on "Surprises in threshold antikaon-nucleon physics"

It has recently been claimed by Oller et al. [PRL 95 (2005) 172502] that the DEAR kaonic hydrogen data can be reconciled with K^- p scattering data in a chiral unitary approach. In this comment we demonstrate that the proposed solution violates fundamental principles of scattering theory.Comment: 1 page, 1 figur