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 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

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

Baryonic R-parity violation and its running

Baryonic R-parity violation arises naturally once Minimal Flavor Violation (MFV) is imposed on the supersymmetric flavor sector at the low scale. At the same time, the yet unknown flavor dynamics behind MFV could take place at a very high scale. In this paper, we analyze the renormalization group (RG) evolution of this scenario. We find that low-scale MFV is systematically reinforced through the evolution, with the R-parity violating couplings exhibiting infrared fixed points. Intriguingly, we also find that if holomorphy is imposed on MFV at some scale, it is preserved by the RG evolution. Furthermore, low-scale holomorphy is a powerful infrared attractor for a large class of non-holomorphic scenarios. Therefore, supersymmetry with minimally flavor violating baryon number violation at the low scale, especially in the holomorphic case but not only, is viable and resilient under the RG evolution, and should constitute a leading contender for the physics beyond the Standard Model waiting to be discovered at the LHC.Comment: 20 pages, 4 figures, to appear in JHE

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

FCNC portals to the dark sector

The most general basis of operators parametrizing a low-scale departure from the SM particle content is constructed. The SM gauge invariance is enforced, and operators of lowest dimensions are retained separately for a new light neutral particle of spin 0, 1/2, 1, and 3/2. The basis is further decomposed into couplings to the SM Higgs/gauge fields, to pairs of quark/lepton fields, and to baryon/lepton number violating combinations of fermion fields. This basis is then used to systematically investigate the discovery potential of the rare FCNC decays of the K and B mesons with missing energy in the final state. The most sensitive decay modes in the s to d, b to d, and b to s sectors are identified and compared for each type of couplings to the new invisible state.Comment: 55 pages. Minor corrections & references added. To appear in JHE