275 research outputs found
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
Field Redefinitions and Wave Function Renormalization to in Heavy Baryon Chiral Perturbation Theory
Mass- and wave-function renormalization is calculated to order in heavy
baryon chiral perturbation theory. Two different schemes used in the literature
are considered. Several technical issues like field redefinitions,
non-transformation of sources as well as subtleties related to the definition
of the baryon propagator are discussed. The nucleon axial-vector coupling
constant is calculated to order as an illustrative example.Comment: 14 pages, Standard Latex. Improved discussion in introduction and
conclusions, phenomenological consequences of corrections to
emphasized. Version published in JHE
Extracting m_s From Flavor Breaking in Hadronic Tau Decays
New finite energy sum rules (FESR's) for extracting m_s from hadronic tau
decay data are constructed which (1) significantly reduce potential theoretical
uncertainties present in existing sum rule analyses and (2) remove problems
associated with both the poor convergence of the OPE representation of the
longitudinal part of the vector and axial vector correlators and the large
statistical errors in the spectral data above the K^* region.Comment: 4 pages, 1 figure. Report of presentations to International
Conference on Quark Nuclear Physics, Adelaide, Feb. 21-25, 2000, 16th
International Conference on Problems in Few-Body Physics, Taipei, March 6-10,
2000, and 7th Conference on the Intersections of Particle and Nuclear
Physics, Quebec City, May 22-28, 200
Strong Isospin-Breaking Effects in K-->pi pi at Next-to-Leading Order in the Chiral Expansion
Strong isospin-breaking (IB) contributions to both the octet and 27-plet weak
K-->2 pi transitions are evaluated at next-to-leading order (NLO) in the chiral
expansion. NLO contributions are shown to significantly reduce the leading
order result for the potentially large contribution to the
amplitude resulting from strong isospin-breaking modifications to the weak
Delta I=1/2 amplitude. The ratio of strong IB 27-plet to strong IB octet
contributions is found to be small for all decay amplitudes. Combined with
recent results on the corresponding electromagnetic contributions, we find that
the ratio of the intrinsic strengths of octet and 27-plet effective weak
operators can be taken to be that obtained from experimental data, analyzed
ignoring isospin breaking, to an accuracy better than of order 10 percent.Comment: 10 pages, 1 figure. NLO determination of strong IB modification of
weak 27-plet transitions now also included; modified phase discussio
The CP-violating asymmetry in K_L -> pi+ pi- e+ e-
We update the theoretical analysis of the CP-violating asymmetry in the decay
K_L -> pi+ pi- e+ e-, relying on chiral perturbation theory and on the most
recent phenomenological information. With the experimentally determined
magnetic amplitude and branching ratio as input, the asymmetry can be
calculated with good accuracy. The theoretical interpretation of the sign of
the asymmetry is discussed.Comment: 11 page
epsilon'/epsilon in the Standard Model
In order to provide an estimate of eps'/eps several effective theories and
physical effects have to be disentangled. In this talk I discuss how it is
possible to predict eps '/eps taking into account all sources of large logs.
The numerical result one obtains, \eps '/\eps \sim (1.7\pm 0.6) \cdot
10^{-4}, is in good agreement with present measurements.Comment: Talk presented at QCD2000, Montpellier july 200
The chiral logs of the K -> pi pi amplitude
I calculate the leading logarithmic contributions up to two-loop order of the
octet part of the K -> pi pi amplitude. This sector of the weak chiral
Lagrangian is believed to be the main source of the enhancement of the I=0
relative to the I=2 K -> pi pi amplitude, the so-called Delta I = 1/2 rule. I
discuss the procedure of chiral extrapolations of lattice data specific to K ->
pi pi decays and study the implication of the present calculation on these
numerically. The latter reinforces the fact that one has to expect a large
enhancement of the I=0 part of the amplitude due to re-scattering effects
between the three mesons.Comment: 20 pages, 4 figures, uses axodra
mu+md from isovector pseudoscalar sum rules
AbstractWe revisit the isovector pseudoscalar sum rule determination of mu+md, using families of finite energy sum rules known to be very accurately satisfied in the isovector vector channel. The sum rule constraints are sufficiently strong to allow a determination of both mu+md and the excited resonance decay constants. The corresponding Borel transformed sum rules are also very well satisfied, providing a non-trivial consistency check on the treatment of direct instanton contributions. We obtain [mu+md](2 GeV)=7.8±1.1 MeV (in the MS scheme), only marginally compatible with the most recent sum rule determinations, but in good agreement with recent unquenched lattice extractions
The DMO Sum Rule Revisited
We reconsider the DMO sum rule in light of our recent two-loop calculations
of isospin and hypercharge vector and axialvector current propagators in chiral
perturbation theory. A modified derivation valid to second order in the light
quark masses is presented, and a phenomenological analysis yields determination
of a combination of finite counterterms occurring in the p^4 and p^6 chiral
lagrangians. Suggestions are given for further study.Comment: 8 pages, LaTeX, 1 tabl
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