1,484 research outputs found
Tau Decay Determination of the Strange Quark Mass
The recent ALEPH measurements of the inclusive Cabibbo--suppressed decay
width of the and several moments of its invariant mass distribution are
used to determine the value of the strange quark mass. We obtain, in the
scheme, MeV, which corresponds to
.Comment: 5pages. Invited talk at QCD'99 (Montpellier, July 1999
Rho Meson Properties in the Chiral Theory Framework
We study the mass, width and couplings of the lightest resonance multiplet
with I(J^{PC})=1(1^{--}) quantum numbers. Effective field theories based on
chiral symmetry are employed in order to describe the form factor associated
with the two-pseudoscalar matrix element of the QCD vector current. The bare
poles of the intermediate resonances are regularized through a
Dyson-Schwinger-like summation. We explore the role of the resonance width in
physical observables and make a coupled-channel analysis of final-state
interactions. This provides many interesting properties, as the pole mass
M_rho{pole}= 764.1 +- 2.7 +4.0-2.5 MeV. At energies E~1 GeV, a second 1(1^{--})
resonance multiplet is considered in order to describe the data in a more
consistent way. From the phenomenologically extracted resonance couplings, we
obtain the chiral coupling L_9^r(mu0)= (7.04 +- 0.05 +0.19-0.27)* 10^{-3}, at
mu0=770$ MeV, and show how the running with the scale mu affects the resonance
parameters. A 1/N_C counting is adopted in this work and the consistency of the
large--N_C expansion is tested. Finally, we make an estimation of the
contribution from diagrams with resonances in crossed channels.Comment: 26 pages, 8 figures, Latex fil
Present Status of Chiral Perturbation Theory
The basic ideas and methods of chiral perturbation theory are briefly
reviewed. I discuss the recent attempts to build an effective Lagrangian in the
resonance region and summarize the known large-N_C constraints on the
low-energy chiral couplings.Comment: 6 pages. Invited talk at the 10th International Symposium on
Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2004), Beijing,
China, August 29 - September 4, 200
Spectral distribution for the decay tau -> nu_tau K pi
With the newly available data sets on hadronic tau decays from the
B-factories BABAR and BELLE, and future data from BESIII, precise information
on the decay distributions will soon become available. This calls for an
improvement of the decay spectra also on the theoretical side. In this work,
the distribution function for the decay tau -> nu_tau K pi will be presented
with the relevant K pi vector and scalar form factors being calculated in the
framework of the resonance chiral theory, also taking into account additional
constraints from dispersion relations and short-distances. As a by-product the
slope and curvature of the vector form factor F_+^{K pi}(s) are determined to
be lambda_+^' = 25.6 10^{-3} and lambda_+^{''} = 1.31 10^{-3} respectively.
From our approach it appears that it should be possible to obtain information
on the low lying scalar K_0^*(800) as well as the second vector K^*(1410)
resonances from the tau decay data. In particular, the exclusive branching
fraction of the scalar component is found to be B[tau -> nu_tau(K pi)_{S-wave}]
= (3.88 +- 0.19) 10^{-4}.Comment: 14 pages, 2 figure
Quantum Loops in the Resonance Chiral Theory: The Vector Form Factor
We present a calculation of the Vector Form Factor at the next-to-leading
order in the 1/N_C expansion, within the framework of Resonance Chiral Theory.
The calculation is performed in the chiral limit, and with two dynamical quark
flavours. The ultraviolet behaviour of quantum loops involving virtual
resonance propagators is analyzed, together with the kind of counterterms
needed in the renormalization procedure. Using the lowest-order equations of
motion, we show that only a few combinations of local couplings appear in the
final result. The low-energy limit of our calculation reproduces the standard
Chiral Perturbation Theory formula, allowing us to determine the resonance
contribution to the chiral low-energy couplings, at the next-to-leading order
in 1/N_C, keeping a full control of their renormalization scale dependence.Comment: 27+1 pages, 9 figure
Form-factors and current correlators: chiral couplings L_10(mu) and C_87(mu) at NLO in 1/N(C)
Using the resonance chiral theory Lagrangian, we perform a calculation of the
vector and axial-vector two-point functions at the next-to-leading order (NLO)
in the 1/N(C) expansion. We have analyzed these correlators within the
single-resonance approximation and have also investigated the corrections
induced by a second multiplet of vector and axial-vector resonance states.
Imposing the correct QCD short-distance constraints, one determines the
difference of the two correlators Pi(t) = Pi_VV(t)- Pi_AA(t) in terms of the
pion decay constant and resonance masses. Its low momentum expansion fixes then
the low-energy chiral couplings L_10 and C_87 at NLO, keeping full control of
their renormalization scale dependence. At mu_0=0.77 GeV, we obtain L_10(mu_0)
= (-4.4 \pm 0.9)10^{-3} and C_87^r(mu_0)=(3.1 \pm 1.1)10^{-5}
Chiral low-energy constants from tau data
We analyze how the recent precise hadronic tau-decay data on the V-A spectral
function and general properties of QCD such as analyticity, the operator
product expansion and chiral perturbation theory (ChPT), can be used to improve
the knowledge of some of the low-energy constants of ChPT. In particular we
find the most precise values of L_{9,10} (or equivalently l_{5,6}) at order p^4
and p^6 and the first phenomenological determination of C_87 (c_50).Comment: Proceedings of the 6th International Workshop on Chiral Dynamics
(Bern, Switzerland, July 6-10, 2009). 9 pages, 3 figure
The hadronic off-shell width of meson resonances
Within the resonance chiral effective theory we study the dressed propagators
of the spin-1 fields, as arise from a Dyson-Schwinger resummation
perturbatively constructed from loop diagrams with absorptive contributions in
the s-channel. We apply the procedure to the vector pion form factor and the
elastic pion-pion scattering to obtain the off-shell width of the rho_0 meson.
We adopt a definition of the off-shell width of spin-1 meson resonances that
satisfies the requirements of analyticity, unitarity, chiral symmetry and
asymptotic behaviour ruled by QCD. To fulfil these constraints the resummation
procedure cannot consist only of self-energy diagrams. Our width definition is
shown to be independent of the formulation used to describe the spin-1 meson
resonances.Comment: 1+12 pages, 4 figures. Minor changes in text. Conclusions unchanged.
Version accepted for publication in Phys. Rev.
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