3,520 research outputs found
Chiral Perturbation Theory for the Quenched Approximation of QCD
[This version is a minor revision of a previously submitted preprint. Only
references have been changed.] We describe a technique for constructing the
effective chiral theory for quenched QCD. The effective theory which results is
a lagrangian one, with a graded symmetry group which mixes Goldstone bosons and
fermions, and with a definite (though slightly peculiar) set of Feynman rules.
The straightforward application of these rules gives automatic cancellation of
diagrams which would arise from virtual quark loops. The techniques are used to
calculate chiral logarithms in , , , and the ratio of
to . The leading
finite-volume corrections to these quantities are also computed. Problems for
future study are described.Comment: 14 page
Isospin Violation in Chiral Perturbation Theory and the Decays \eta \ra \pi \ell \nu and \tau \ra \eta \pi \nu
I discuss isospin breaking effects within the standard model. Chiral
perturbation theory presents the appropriate theoretical framework for such an
investigation in the low--energy range. Recent results on the electromagnetic
contributions to the masses of the pseudoscalar mesons and the
amplitudes are reported. Using the one--loop formulae for the
form factors, rather precise predictions for the decay rates of can be obtained. Finally, I present an estimate of
the \tau \ra \eta \pi \nu branching ratio derived from the dominant meson
resonance contributions to this decay.Comment: 10 pages, latex, one figure available upon reques
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
The Goldberger -- Treiman Relation, and at
The Goldberger-Treiman relation is shown to persist in the chiral limit at
finite temperatures to order . The dependence of turns out to
be the same as for , , while is temperature independent to this order. The baryon octet and
couplings also behave as if only pions are massless in the
pseudoscalar meson octet.Comment: 7p, NSF-ITP-93-145, BUTP-93/27, PUTP-1433, November 199
The anomalous chiral perturbation theory meson Lagrangian to order revisited
We present a revised and extended construction of the mesonic Lagrangian
density in chiral perturbation theory (ChPT) at order in the anomalous
(or epsilon) sector, . After improving several aspects
of the strategy we used originally, i.e., a more efficient application of
partial integration, the implementation of so-called Bianchi identities, and
additional trace relations, we find the new monomial sets to include 24
, 23 SU(3), and 5 SU(2) elements. Furthermore, we introduce 8
supplementary terms due to the extension of the chiral group to .Comment: 21 pages, Latex, using RevTe
Pion mass dependence of the semileptonic scalar form factor within finite volume
We calculate the scalar semileptonic kaon decay in finite volume at the
momentum transfer , using chiral perturbation
theory. At first we obtain the hadronic matrix element to be calculated in
finite volume. We then evaluate the finite size effects for two volumes with and and find that the difference between the finite
volume corrections of the two volumes are larger than the difference as quoted
in \cite{Boyle2007a}. It appears then that the pion masses used for the scalar
form factor in ChPT are large which result in large finite volume corrections.
If appropriate values for pion mass are used, we believe that the finite size
effects estimated in this paper can be useful for Lattice data to extrapolate
at large lattice size.Comment: 19 pages, 5 figures, accepted for publication in EPJ
Contributions of order to form factors and unitarity of the CKM matrix
The form factors for the semileptonic decay are computed to
order in generalized chiral perturbation theory. The main difference
with the standard expressions consists in contributions quadratic in
quark masses, which are described by a single divergence-free low-energy
constant, . A new simultaneous analysis is presented for the CKM matrix
element , the ratio , decay rates and the
scalar form factor slope . This framework easily accommodates the
precise value for deduced from superallowed nuclear -decays
Aspects of Chiral Dynamics
I discuss several topics in chiral perturbation theory - in particular, I
recall pecularities of the chiral expansion in the baryon sector.Comment: 14 pages, Latex with lamuphys.sty, 3 figures embedded with
epsfig.sty. To appear in Proc. of Workshop on Chiral Dynamics 1997, Mainz,
Germany, Sept. 199
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
Critical Analysis of Baryon Masses and Sigma-Terms in Heavy Baryon Chiral Perturbation Theory
We present an analysis of the octet baryon masses and the and
--terms in the framework of heavy baryon chiral perturbation theory. At
next-to-leading order, , knowledge of the baryon masses and
allows to determine the three corresponding finite
low--energy constants and to predict the the two --terms
. We also include the spin-3/2 decuplet in the
effective theory. The presence of the non--vanishing energy scale due to the
octet--decuplet splitting shifts the average octet baryon mass by an infinite
amount and leads to infinite renormalizations of the low--energy constants. The
first observable effect of the decuplet intermediate states to the baryon
masses starts out at order . We argue that it is not sufficient to retain
only these but no other higher order terms to achieve a consistent description
of the three--flavor scalar sector of baryon CHPT. In addition, we critically
discuss an SU(2) result which allows to explain the large shift of via intermediate states.Comment: 18 pp, TeX, BUTP-93/05 and CRN-93-0
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