Related papers: Obtaining K to pi pi from Off-Shell K to pi Amplit…
An overview is presented about old and recent methods to compute the $K\to \pi \pi$ decay amplitude.
A phenomenological analysis of $K\to \pi\pi\gamma$ ($K_L\to\pi^+\pi^-\gamma$ and $K^+\to\pi^+\pi^0\gamma$) with the direct emission photon is carried out beyond the leading order in the chiral perturbation theory. We show that the…
We first review the current algebra - PCAC approach to nonleptonic octet baryon 14 weak decay B (\to) (B^{\prime})(\pi) amplitudes. The needed four parameters are independently determined by (\Omega \to \Xi \pi),(\Lambda K) and (\Xi ^{-}\to…
We have calculated the decay amplitude for the process $K_{S}$ $\to$ $\gamma \gamma$ at one loop order in chiral perturbation theory. As a new improvement we have included the weak mass term which is only relevant for processes with…
The decays $K \to \pi l^{+} l^{-}$, $K \to \pi \gamma \gamma $ and $K \to \pi \nu {\bar \nu}$ are investigated using the higher order terms of the chiral perturbation theory. The counterterms induced by strong, weak and electromagnetic…
Threshold expansions of the $\pi\pi$ and $K\overline{K}$ spin 0 and isospin 0 scattering amplitudes are performed. Scattering lengths, effective ranges and so--called volume parameters are evaluated. Good agreement with the existing…
We perform a chiral extrapolation of lattice data on the scalar K pi form factor and the ratio of the kaon and pion decay constants within Chiral Perturbation Theory to two loops. We determine the value of the scalar form factor at zero…
Starting from the Chiral Perturbation Theory Lagrangian, but keeping different masses for the charged and neutral mesons, and using a previously developed non-perturbative unitary scheme that generates the lightest meson-meson resonances,…
The $\gamma\gamma \to \pi^0 \pi^0 \pi^0$ and $\gamma\gamma \to \pi^+ \pi^- \pi^0$ amplitudes are discussed in the general context of Chiral Perturbation Theory (ChPT) to $O(p^6)$. Chiral loops are found to play a major role. This makes…
We have used a conventional model for the $pp \rightarrow pp \pi^{0}$ reaction consisting of the Born term plus the $s$-wave rescattering term. As a novelty we have introduced the off shell dependence of the $\pi N$ $s$-wave isoscalar…
Pion-kaon ($\pi K$) pairs occur frequently as final states in heavy-particle decays. A consistent treatment of $\pi K$ scattering and production amplitudes over a wide energy range is therefore mandatory for multiple applications: in…
We calculate the logarithmic corrections to the matrix elements for $K^+\to\pi^+$ and $K\to$vacuum (which are used on the lattice to determine $K\to\pi\pi$ amplitudes), in one-loop quenched and unquenched Chiral Perturbation Theory. We find…
We show that lattice calculation of K --> pi pi and $epe$ amplitudes for (8,1) and (27,1) operators to O(p^4) in chiral perturbation theory is feasible when one uses K --> pi pi computations at the two unphysical kinematics allowed by the…
The CP conserved non leptonic $K\to \pi \pi \pi$ decays are discussed within the chiral quark model, including chiral perturbation theory corrections. All amplitudes are parameterized in terms of quark and gluon condensate and the…
The $\eta \to \pi^+ \pi^- \pi^0 \gamma$ decay is discussed in the general context of Chiral Perturbation Theory (ChPT), assuming that the low--energy constants (counter--terms) are saturated by vector-meson resonances. The $\eta \to \pi^+…
We propose an approach for calculating $K\to\pi\pi$ decays to the next-to-leading order in chiral expansion. A detailed numerical study of this approach is being performed.
The $\gamma^* \pi^0 \rightarrow \gamma$ form factor, including the extension off the pion mass-shell, is obtained from a generalized impulse approximation within a QCD-based model field theory known to provide an excellent description of…
We update the numerical results for the s-wave pi pi scattering phase-shift difference delta_0^0 - delta_0^2 at s = m_K^2 from a previous study of isospin breaking in K to 2 pi amplitudes in chiral perturbation theory. We include recent…
The amplitudes for the rare decay modes $K^\pm\to\pi^\pm\ell^+\ell^-$ and $K_S\to\pi^0\ell^+\ell^-$ are studied with the aim of obtaining predictions for them, such as to enable the possibility to search for violations of lepton-flavour…
A recently proposed set of sum rules, based on the pion-Kaon scattering amplitudes and their crossing-symmetric conjugates are analysed in detail. A key role is played by the $l=0$ $\pi\pi\to K\overline K$ amplitude which requires an…