Recent developments in rare kaon decays

We discuss issues in rare and radiative kaon decays. The interest is to extract useful short-distance information and uncover underlying dynamics. We emphasize channels where either we can understand non-perturbative aspects of QCD or there is a chance to test the Standard Model.Comment: Invited minireview for Modern Physics Letters A (MPLA), 15 pages, 9 figures, usepackages epsf,colo

Electromagnetic penguin operators and direct CP violation in K --> pi l^+ l^-

Supersymmetric extensions of the Standard Model predict a large enhancement of the Wilson coefficients of the dimension-five electromagnetic penguin operators affecting the direct CP violation in K_L --> pi^0 e^+ e^- and the charge asymmetry in K^\pm --> pi^\pm l^+ l^-. Here we compute the relevant matrix elements in the chiral quark model and compare these with the ones given by lattice calculationsComment: 12 pages, JHEP style, gluonic corrections to B_T adde

Radiative Non-Leptonic Kaon Decays

We investigate to what extent DA$\Phi$NE will be able to test the Standard Model in the confinement regime with radiative kaon decays. We concentrate on processes which can be detected at DA$\Phi$NE and we review briefly those decays where only upper limits can be expected. The Standard Model predictions for these decays are analyzed in the framework of chiral perturbation theory.Comment: 41 pages, latex file, 10 figures added in a separate uufil

Supersymmetric contributions to direct CP violation in K -> pi pi gamma decays

We analyze the supersymmetric contributions to direct-CP-violating observables in $K \to \pi\pi\gamma$ decays induced by gluino-mediated magnetic-penguin operators. We find that \epsp_{+-\gamma} and the differential width asymmetry of $K^\pm \to \pi^\pm \pi^0 \gamma$ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where \epsp/\eps is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in $|\Delta S|=1$ transitions, complementary to \epsp/\eps and rare decays.Comment: 14 pages, Latex. Numerical error in Eq.(36) corrected, conclusions unchanged; version to appear in Phys. Lett.

Radiative Four--Meson Amplitudes in Chiral Perturbation Theory

We present a general discussion of radiative four--meson processes to $O(p^4)$ in chiral perturbation theory. We propose a definition of ``generalized bremsstrahlung'' that takes full advantage of experimental information on the corresponding non--radiative process. We also derive general formulae for one--loop amplitudes which can be applied, for instance, to \eta \ra 3\pi\gamma, \pi \pi \ra \pi \pi \gamma and K \ra 3\pi\gamma.Comment: 8 pages, LaTex file, 1 figure. Full postscript version at this URL http://hpteor.lnf.infn.it/dafnepapers.htm

A search for Z' in muon neutrino associated charm production

In many extensions of the Standard Model the presence of an extra neutral boson, Z', is invoked. A precision study of weak neutral-current exchange processes involving only second generation fermions is still missing. We propose a search for Z' in muon neutrino associated charm production. This process only involves Z' couplings with fermions from the second generation. An experimental method is thoroughly described using an ideal detector. As an application, the accuracy reachable with present and future experiments has been estimated.Comment: 13 pages, 3 figures, late