Higgs--mediated K -> pi nu nu-bar in the MSSM at large tan(beta)

We analyze the impact of Higgs-mediated amplitudes on the rare decays KL -> pi0 nu nu-bar and K+ -> pi+ nu nu-bar in the MSSM with large tan(beta) and general flavour mixing. We point out that, going beyond the minimal flavour violation hypothesis, Z-penguin amplitudes generated by charged-Higgs exchange can induce sizable modifications of K -> pi nu nu-bar rates. Interestingly, these effects scale as tan^4(beta) at the amplitude level. For large values of tan(beta), this mechanism allows deviations from the SM expectations even for tiny (CKM-type) off-diagonal mixing terms in the right-handed squark sector.Comment: 9 pages, 2 figure

Weak decays of pseudo Goldstone bosons

A short overview of recent progress in describing kaon and pion decays within Chiral Perturbation Theory is presented. Particular attention is devoted to the issues of final-state interactions and isospin breaking in $K \to 2 \pi$, as well as to the estimate of long-distance contributions in $K \to \ell^+\ell^- (\pi)$.Comment: 13 pages, invited talk at Chiral Dynamics 2000, Newport News, USA, 17-22 July 200

Flavour Physics and Implication for New Phenomena

Flavour physics represents one of the most interesting and, at the same time, less understood sector of the Standard Theory. On the one hand, the peculiar pattern of quark and lepton masses, and their mixing angles, may be the clue to some new dynamics occurring at high-energy scales. On the other hand, the strong suppression of flavour-changing neutral-current processes, predicted by the Standard Theory and confirmed by experiments, represents a serious challenge to extend the Theory. This article reviews both these aspects of flavour physics from a theoretical perspective.Comment: Contribution to "The Standard Theory up to the Higgs discovery - 60 years of CERN", Ed. by L. Maiani and G. Rolandi (v2: minor typos corrected

Supersymmetric effects in rare semileptonic decays of B and K mesons

Rare flavour-changing neutral-current transitions of the type $s \to d \ell^+\ell^-(\nu\bar\nu)$ and $b \to s \ell^+\ell^-(\nu\bar\nu)$ are analysed in supersymmetric extensions of the Standard Model with generic flavour couplings. It is shown that these processes are particularly sensitive to the left--right mixing of the squarks and that, in the presence of non-universal $A$ terms, they could lead to unambiguous signatures of new physics in exclusive $K$ and $B$ meson decays.Comment: 15 pages, Latex, invited talk at RADCOR 2000 (Carmel CA, USA, Sept. 2000

The Challenges of Flavour Physics

The open problems and the most recent developments in flavour physics are briefly reviewed. Particular attention is devoted to the current "anomalies" in the CKM picture and their possible interpretation in beyond-the-Standard-Model frameworks.Comment: 13 pages, plenary talk at ICHEP 2010 (Paris, July 22-28, 2010). V2: A few typos corrected and a few refs adde

Theory of radiative and rare B decays

We present a concise theoretical overview of radiative and rare B decays mediated by flavour-changing neutral-current transitions of the type b->s(d)gamma and b->s(d)l+l-.Comment: 7 pages, 4 figures. Talk given at 9th International Conference on B Physics at Hadron Machines (Beauty 2003), Pittsburgh, Pennsylvania, 14-18 Oct 200