We have calculated the form-factors F and G in K → ππlν decays (K(l4)) to two-loop order in Chiral Perturbation Theory (ChPT). Combining this together with earlier two-loop calculations an updated set of values for the L(i)/(r), the ChPT constants at O(p4), is obtained. We discuss the uncertainties in the determination and the changes compared to previous estimates. (C) 2000 Elsevier Science B.V.

The F and G form-factors of Kℓ4 and the quark condensates are calculated to O(p6) in Chiral Perturbation theory (CHPT). Full formulas are presented as much as possible. A full refit of most of the O(p4) CHPT parameters is done with a discussion of all inputs and underlying assumptions. We discuss the consequences for the vacuum expectation values, decay constants, pseudoscalar masses and π - π sca

We discuss various models and chiral perturbation theory results for the K14 form factors F and G. We check to what extent a simple parametrization with a few parameters can be used to extract information from experiment.

We construct the effective chiral lagrangean for chiral perturbation theory in the mesonic even-intrinsic-parity sector at order p6. The lagrangean contains 112 in principle measurable + 3 contact terms for the general case of n light flavours, 90+4 for three and 53+4 for two flavours. The equivalence between equations of motion and field redefinitions to remove spurious terms in the lagrangeans i

We calculate the vector and scalar form factors of the pion to two loops in Chiral Perturbation Theory. We estimate the unknown O(p6) constants using resonance exchange. We make a careful comparison to the available data and determine two O(p4) constants rather precisely, and two O(p6) constants less precisely. We also use Chiral Perturbation Theory to two loops to extract in a model-independent m

We show how to obtain a "heavy" meson effective lagrangian for the case where the number of heavy particles is not conserved. We apply the method in a simple example at tree level and perform then the reduction for the case of vector mesons in Chiral Perturbation Theory in a manifestly chiral invariant fashion. Some examples showing that "heavy" meson effective theory also reproduces the correct n

We determine the full structure of the leading (double-pole) divergences of O(p6) in the meson sector of chiral perturbation theory. The field theoretic basis for this calculation is described. We then use an extension of this result to determine the p6 contributions containing double chiral logarithms (L2), single logarithms times p4 constants (L × Lr i) and products of two p4 constants (Lr i × L

We calculate the leading quark mass corrections of order mqlog(mq), mq and m3/2 q to the vector meson decay constants within heavy vector meson chiral perturbation theory. We discuss the issue of electromagnetic gauge invariance and the heavy mass expansion. Reasonably good fits to the observed decay constants are obtained.

We properly define off-shell K → π transition amplitudes and use them to extract information for on-shell K → ππ amplitudes within Chiral Perturbation Theory. At order p2 in the chiral expansion all three parameters of weak interaction can be determined. At order p4 we are able to fix eleven additional constants out of thirteen contributing to off-shell K → π transitions, which leaves four undeter

Within Chiral Perturbation Theory (CHPT) we compute the form factors A, V and γ = A/V in the π → lνγ decay to O(p6). A and γ obtain corrections of order 25%.

We present technical details of the evaluation of the elastic ππ scattering amplitude to two loops in chiral perturbation theory. In particular, we elaborate on the renormalization procedure at the two-loop order and on the evaluation of the relevant Feynman diagrams that can all be expressed in terms of elementary functions. For the sake of clarity, we discuss these matters both in the N-componen

We discuss the vector meson masses within the context of chiral perturbation theory performing an expansion in terms of the momenta, quark masses and 1/Nc. We extend the previous analysis to include isospin breaking effects and also include up to order p4. We discuss vector meson chiral perturbation theory in some detail and present a derivation from a relativistic Lagrangian. The unknown coeffici

Chiral perturbation theory relates the |S|=2 matrix element K0|(sd)V-A×(sd)V-A|K0 to the |S|=1 matrix element +0|(sd)V-A(uu)V-A+(su)V- A×(ud)V-A-(sd)V-A(dd)V-A|K+. The latter matrix element is measured in K++0 decay and the former matrix element is relevant for the predictions that the standard model makes for CP nonconservation in K0-K0 mixing. In this paper the corrections of order mK4 lnmK2 to

We discuss hyperon decays and hyperon magnetic moments using a chiral lagrangian where the baryons appear as solitons. Some relations are derived using the semiclassical approximation.

The contribution of electromagnetic "Penguin"-type diagrams to ε{lunate}′/ε{lunate} is examined in the standard six-quark model.

The predictions of chiral perturbation theory for the weak non-leptonic decays of hyperons are examined beyond the leading order. For the S-wave amplitudes we find that the leading corrections to lowest order chiral perturbation theory preserve the vanishing of the Σ+ → nπ+ amplitude. However, the Lee-Sugawara relation gets a large correction indicating a breakdown of chiral perturbation theory fo

A new scenario accounting for the production of monojets with large missing transverse energy is described and a specific model implementing it is constructed. The production rate for monojets is calculated.