5 research outputs found
Phenomenology of the <VVP> Green's function within the Resonance Chiral Theory
We analyse the odd-intrinsic-parity effective Lagrangian of QCD valid for
processes involving one pseudoscalar with two vector mesons described in terms
of antisymmetric tensor fields. Substantial information on the
odd-intrinsic-parity couplings is obtained by constructing the
vector-vector-pseudoscalar Green's three-point function, at leading order in
1/N_C, and demanding that its short-distance behaviour matches the
corresponding OPE result. The QCD constraints thus enforced allow us to predict
the decay amplitude omega -> pi gamma, the O(p^6) corrections to pi -> gamma
gamma and the slope parameter in pi -> gamma gamma^*.Comment: 4 pages, 1 figure. Talk given at QCD 03: High-Energy Physics
International Conference in Quantum Chromodynamics, Montpellier, France, 2-8
Jul 200
Towards a determination of the chiral couplings at NLO in 1/N(C): L_8(mu) and C_38(mu)
We present a dispersive method which allows to investigate the low-energy
couplings of chiral perturbation theory at the next-to-leading order (NLO) in
the 1/N(C) expansion, keeping full control of their renormalization scale
dependence. Using the resonance chiral theory Lagrangian, we perform a NLO
calculation of the scalar and pseudoscalar two-point functions, within the
single-resonance approximation. Imposing the correct QCD short-distance
constraints, one determines their difference Pi(t)=Pi_S(t)-Pi_P(t) in terms of
the pion decay constant and resonance masses. Its low momentum expansion fixes
then the low-energy chiral couplings L_8 and C_38. At mu_0=0.77 GeV, we obtain
L_8(mu_0)^{SU(3)} = (0.6+-0.4)10^{-3} and C_{38}(mu_0)^{SU(3)}=(2+-6)10^{-6}.Comment: Extended version published at JHEP01(2007)039. A NLO prediction for
the O(p6) chiral coupling C_38 has been added. The original L_8 results
remain unchange
Form Factors in the radiative pion decay
We perform an analysis of the form factors that rule the structure-dependent
amplitude in the radiative pion decay. The resonance contributions to pion -> e
nu_e gamma decays are computed through the proper construction of the vector
and axial-vector form factors by setting the QCD driven asymptotic properties
of the three-point Green functions VVP and VAP, and by demanding the smoothing
of the form factors at high transfer of momentum. A comparison between
theoretical and experimental determinations of the form factors is also carried
out. We also consider and evaluate the role played by a non-standard tensor
form factor. We conclude that, at present and due to the hadronic incertitudes,
the search for New Physics in this process is not feasible.Comment: 14 pages, no figures. Typos corrected. Accepted for publication in
The European Physical Journal