We calculate within chiral perturbation theory the cross section for γγ→π0π0 and γγ→π+π- to next-to-leading order. The first process only depends on the one-loop contributions and forms a test of chiral perturbation theory. We also calculate the pion electromagnetic form factor and compare it to recent data.

We present a discussion of the treatment of 1 Nc-corrections in chiral perturbation theory for nonleptonic weak processes. We compare the approach with an explicit cutoff and dimensional regularization in chiral perturbation theory and present evidence that they are equivalent. The quadratic dependence on the cutoff can be subtracted consistently at each level of 1 Nc. We discuss the identificatio

We study the value of the light quark masses combination mu + md in QCD using both Finite Energy Sum Rules and Laplace Sum Rules. We have performed a detailed analysis of both the perturbative QCD and the hadronic parametrization inputs needed in these Sum Rules. As main result, we obtain mu (1 GeV2 + md (1 GeV2) = (12 ± 2.5) MeV for the running MS masses.

The two-point functions in generalized Nambu-Jona-Lasinio models are calculated to all orders in momenta and quark masses to leading order in 1/Nc. The use of Ward identities and the heat-kernel expansion allows for a large degree of regularization independence. We also show how this approach works to the same order for three-point functions on the example of the vectorpseudoscalar-pseudoscalar th

The matrix elements for K → ππlν decays are described by four form factors F, G, H and R. We complete previous calculations by evaluating R at next-to-leading order in the low-energy expansion. We then estimate higher order contributions using dispersion relations and determine the low-energy constants L1, L2 and L3 from data on Ke4 decays and on elastic pion scattering. Finally, we present predic

We show how the effective action of the Extended Nambu-Jona-Lasinio model (ENJL) can be defined in the presence of anomalies in a way that reproduces the flavour anomaly. This necessarily breaks Vector Meson Dominance (VMD) in the usual sense. The same method can be used to construct other chiral effective theories involving constituent quarks and spin-1 mesons that give the correct flavour anomal

We discuss vector, axial-vector, scalar and pseudoscalar two-point functions at low and intermediate energies. We first review what is known from chiral perturbation theory, as well as from a heat kernel expansion within the context of an extended Nambu-Jona-Lasinio (ENJL) model. We derive then these two-point functions to all orders in the momenta and to leading order in 1/N c within the framewo

We evaluate the matrix elements for the radiative kaon decays K+ → l+νlγ, l+νll′+l′- and K → πlνlγ (l, l′ = e, μ) to next-to-leading order in chiral perturbation theory. We calculate total rates and rates with several kinematical cuts and confront the results with existing data. Measurements at future kaon facilities will allow for a more detailed comparison between theory and experiment.

We calculate the O(p6) corrections to the anomalous form factors appearing in π+, K+ → e+νγ, μ+νγ and K14 decays in chiral perturbation theory. The relevant dimension 6 terms of the lagrangian are evaluated assuming their saturation by the vector meson contribution.

We present a derivation of the low-energy effective action of an extended Nambu-Jona-Lasinio (ENJL) model to O(p4) in the chiral counting. Two alternative scenarios are considered on how the ENJL model could originate as a low-energy approximation to QCD. The low-energy effective lagrangian we derive includes the usual pseudoscalar Goldstone modes, as well as the lower scalar, vector and axial-vec

The BK parameter is discussed in the general context of calculating beyond the factorization approximation for hadronic matrix elements. A variant of the 1 Nc method of Bardeen et al. is used. We present calculations within a low energy approach and a calculation within the Nambu-Jona-Lasinio model. Matching with the QCD behaviour and dependence on non-zero current quark masses is studied.

Recent measurements of the transition form factors for the P* vertices, with P=0, and are compared with different models. These include vector-meson dominance, constituent-quark loops, the QCD-inspired interpolation by Brodsky-Lepage, and chiral perturbation theory. General agreement is observed and differencesdue to SU(3) breaking are stressed and discussed.

The η→π0γγ decay amplitude is discussed in the general context of chiral perturbation theory assuming that the low-energy constants (counterterms) are saturated by the known meson resonances. The suppression of the lowest order contributions is understood in physical terms. A reasonable agreement with the experimental decay width is achieved.

The interplay between the chiral anomaly and the non-leptonic weak hamiltonian is studied. The structure of the corresponding effective lagrangian of odd intrinsic parity is established. It is shown that the factorizable contributions (leading in 1/Nc) to that lagrangian can be calculated without free parameters. As a first application, the decay K+→π+π0γ is investigated.

We have calculated the decay rates of the Bs meson in a number of exclusive two-body decay channels using the Bauer-Stech-Wirbel model for current matrix elements. The influence of the free parameters of the model on the predictions is studied. The total branching ratio of the Bs into final states which only contain stable particles is found to be about 10-3.

All the terms needed to cancel the divergences appearing in one-loop calculations involving the Wess-Zumino term are obtained. We apply this result to the Pγγ and PPPγ vertices, fixing the finite part of the coefficients of the O(p6) terms in the lagrangian with vector meson contributions. In all the cases the corrections improve the agreement between the theoretical predictions and experimental d

The matching of the log and short distance contributions to the KL-KS mass difference is investigated in the large Nc limit (Nc being the number of colours). In this limit a physically well defined separation between the two regimes exists. This allows for an investigation of the matching between the two contributions. We obtain that 0.8±0.1 of the observed mass difference is due to the light and

We consider the process 00 within the quark model. We find small corrections to the lowest-order result obtained from chiral loops. These corrections are very similar to those found in vector-meson-dominated models, and too small to be tested with the present data. We use this result, together with a simple pole model, to find the amplitude for KL0 and use this to estimate the CP-conserving part o

We calculate the BK parameter within the framework of the 1/Nc expansion. We essentially use the technique presented by Bardeen, Buras and Gérard but calculate an off-shell Green function in order to disentangle different contributions. We study this Green function in pure Chiral Perturbation Theory (CHPT) first and afterwards in the 1/Nc expansion in the presence of an explicit cut-off to determi

Introduction: Massive bleeding is a serious complication associated with impaired survival after surgery for acute type A aortic dissection (ATAAD). There are no previous reports evaluating the effect of ATAAD and associated surgery on von Willebrand factor (VWF). The aim of the present study was to analyze VWF activity (VWF:GPIbM) and thus the potential of Factor (F) VIII/VWF concentrate as a tre