433 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
Reordering of Baryon Chiral Perturbation Theory
Reordering of the chiral perturbation series, proposed recently by Becher and
Leutwyler in the framework of SU(2) baryonic ChPT, is applied to the SU(3)
case. This results in improved convergence of the chiral expansion of static
properties of the lowest lying baryon octet, which in most cases is quite
impressive. Finite renormalization of coupling constants and the role it plays
in the interpretation of effective field theories is discussed. Some future
tests of the viability of the scheme are proposed too.Comment: 9 pages, one reference adde
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
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
Finite volume effects using lattice chiral perturbation theory
Lattice regularization is used to perform chiral perturbation theory
calculations in finite volume. The lattice spacing is chosen small enough to be
irrelevant, and numerical results are obtained from simple summations.Comment: Lattice2004(spectrum), 3 page
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
Baryon self energies in the chiral loop expansion
We compute the self energies of the baryon octet and decuplet states at the
one-loop level applying the manifestly covariant chiral Lagrangian. It is
demonstrated that expressions consistent with the expectation of power counting
rules arise if the self energies are decomposed according to the
Passarino-Veltman scheme supplemented by a minimal subtraction. This defines a
partial summation of the chiral expansion. A finite renormalization required to
install chiral power counting rules leads to the presence of an infrared
renormalization scale. Good convergence properties for the chiral loop
expansion of the baryon octet and decuplet masses are obtained for natural
values of the infrared scale. A prediction for the strange-quark matrix element
of the nucleon is made.Comment: 36 pages, 4 figures, 8 tables. The revised manuscript contains a
proof that given any one-loop integral that arises when computing one-baryon
processes it is sufficient to renormalize the scalar master-loop functions of
the Passarino-Veltman reduction in a manner that the latter are compatible
with the expectation of chiral counting rule
- …