264 research outputs found
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 --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
- …