Very low energy matching of effective meson theories with QCD

A simple matching procedure is proposed to extract constraints on effective meson theories. In this way, a QCD prediction for the pion decay constant is found, F(pi)=2 m(pi)/pi, i.e. approximately 90MeV. The same procedure also determines other mesonic observables, like the decay width of the sigma meson to two photons. Finally, some information which can be gained about the hadronic light-by-light contributions to the muon anomalous moment are briefly commented.Comment: 6 pages, 2 eps figure

Rare K and B decays with non-standard missing energy

The rare K and B semileptonic decays into neutrino pairs are well-known to be extremely sensitive to non-standard physics in the quark sector. In this talk, their capabilities to signal New Physics in the leptonic sector, or even to reveal entirely new invisible sectors, are analyzed.Comment: Talk given at CKM2010, 6th International Workshop on the CKM Unitarity Triangle, University of Warwick, UK, 6-10 September 201

Minimal Flavor Violation as an alternative to R-parity

A peculiar aspect of the MSSM, the simplest supersymmetric extension of the Standard Model, is that it is usually defined including an ad hoc symmetry, R-parity, whose sole purpose is to forbid rapid proton decay. This symmetry deeply alters the phenomenology of the MSSM, and renders the experimental search strategies quite involved. Besides, the MSSM suffers from a number of flavor puzzles. Generically, the superparticle contributions to Flavor Changing Neutral Currents (FCNC) are too large compared to experiment, both in the quark and lepton sectors. The Minimal Flavor Violation (MFV) hypothesis aims at suppressing these contributions, and when enforced as a symmetry principle, achieves this in a very natural and systematic way. In this talk, it will be shown that imposing MFV is not only able to suppress supersymmetric contributions to FCNC, it also naturally explains the apparent stability of the proton. As a result, R-parity can be avoided altogether, motivating the search for supersymmetry through simpler channels, like for example single stop resonant production, whose strength is predicted by MFV.Comment: Parallel talk given at the 34th International Conference on High Energy Physics (ICHEP08), 29 July - 5 August 2008, Philadelphia, USA. 5 pages, 1 figur

Proton stability from a fourth family

The possibility to violate baryon or lepton number without introducing any new flavor structures, beyond those needed to account for the known fermion masses and mixings, is analyzed. With four generations, but only three colors, this minimality requirement is shown to lead to baryon number conservation, up to negligible dimension-18 operators. In a supersymmetric context, this same minimality principle allows only superpotential terms with an even number of flavored superfields, hence effectively enforces R-parity both within the MSSM and in a GUT context.Comment: Revised and extended. To appear in Phys. Rev.

Recent progress on supersymmetric effects in rare K decays

The dominant MSSM effects in the rare K decays, K+ --> pi+ nu nu bar, KL --> pi0 nu nu bar, KL --> pi0 e+ e- and KL --> pi0 mu+ mu-, are discussed both within and without the minimal flavor violation hypothesis, at moderate and large tangent beta. In each case, the sensitivities to MSSM soft-breaking terms are compared, laying emphasis on possible correlations among observables. In most scenarios, rare K decays offer unique windows into the Delta S=1 sector of the soft-breaking terms. Therefore, together with B-physics and collider observables, these modes will be essential for reconstructing the still elusive SUSY-breaking mechanism.Comment: Talk given at the KAON07 International Conference, May 21-25 2007, Frascati, Ital

Rare K decays in the Standard Model

The very clean theoretical predictions for the rare decays K --> pi nu nu_bar and KL --> pi0 l+ l- are reviewed, and their various theoretical inputs summarized. The less favorable situation for KL --> mu+ mu- is also commented.Comment: Talk given at 4th International Workshop on the CKM Unitarity Triangle (CKM 2006), Nagoya, Japan, 12-16 Dec 200