3,687 research outputs found
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
Chiral perturbation theory with Wilson-type fermions including effects: degenerate case
We have derived the quark mass dependence of , and
, using the chiral perturbation theory which includes the effect
associated with the explicit chiral symmetry breaking of the Wilson-type
fermions, in the case of the degenerate quarks. Distinct features of
the results are (1) the additive renormalization for the mass parameter
in the Lagrangian, (2) corrections to the chiral log ()
term, (3) the existence of more singular term, , generated by
contributions, and (4) the existence of both and terms
in the quark mass from the axial Ward-Takahashi identity, . By
fitting the mass dependence of and , obtained by the
CP-PACS collaboration for full QCD simulations, we have found that the
data are consistently described by the derived formulae. Resumming the most
singular terms , we have also derived the modified formulae, which
show a better control over the next-to-leading order correction.Comment: 21 pages, 4 figures (10 eps files), Revtex4, some discussions and
references added, the final version to appear in PR
Chiral Corrections to Lattice Calculations of Charge Radii
Logarithmic divergences in pion and proton charge radii associated with
chiral loops are investigated to assess systematic uncertainties in current
lattice determinations of charge radii. The chiral corrections offer a possible
solution to the long standing problem of why present lattice calculations yield
proton and pion radii which are similar in size.Comment: PostScript file only. Ten pages. Figures included. U. of MD Preprint
#92-19
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 , arising from the contribution of
low-momentum virtual pions to the sigma commutator. Chiral symmetry
requires that no term of this order appears in the 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
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
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
Pion Mass Effects in the Large Limit of \chiPT
We compute the large effective action of the non-linear
sigma model including the effect of the pion mass to order
. 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 .
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
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