A. Masiero

Effects of supergravity-induced electroweak breaking on rare b-decays and mixings

We perform a complete computation of the contributions to b → s + γ, b → s/+/−, b → sνν, b → s + g, Bdo−Bdo and Bso−Bso in minimal spontaneously broken N = 1 supergravity with radiative breaking of the electroweak symmetry group. We compare our results with previous evaluations in non-minimal and minimal supersymmetric models, where the constraint of the SU(2)L × U(1)Y radiative breaking was not imposed. The possibilities of disentangling supersymmetry from the Standard Model in the experimental searches for the abovementioned rare processes are discussed.

New constraints on squark and gluino masses from radiative b decays

Abstract We show on general grounds that radiative mesonic decays, mediated through penguin-like diagrams, are expected to exhibit a significant enhancement from the exchange of supersymmetric particles. An interesting example is the decay b→sγ. An experimental bound BR(B→K ∗ γ) ⩽ 10 −3 is presently available. It is however unclear whether K ∗ γ represents the dominant mode for the inclusive b→sγ decay. We show that an upper bound BR(b→sγ) −3 leads, for m t ⋍ 45–80 GeV, to bounds on squarks and gluino masses comparable to the one coming from the analysis of the monojet events at the CERN pp collider.

Supersymmetric enhancement of non-charmed B-decays

Abstract We study the non-charmed strange decays of the B meson in the context of low-energy minimal N = 1 supergravity. We find that the inclusive channel b → s gluon is greatly enhanced with respect to the standard model prediction. Indeed, for gluino and squark masses of 60–80 GeV and a top mass between 50 and 80 GeV, a branching ratio as high as 10–30% can be reached. This opens a new window for the possibility of testing the presence of new physics in low-energy phenomenology. A comparative review of the standard model results is presented.

Constraints on supersymmetry from rare kaon decays

Abstract The supersymmetric contributions to K + →π + + “nothing” decays are analyzed in the context of low energy spontaneously broken N = 1 supergravity models. It is found that the leading supersymmetric contributions to K + →π + ν ν can be at most of the same order as the standard model contributions with three generations. On the other hand a large enhancement for K + →π + g g g g (photono) is present. The constraints that the planned BNL experiment can impose on this class of models are commented on.

B0 − B̄0 mixing and related CP violation in supersymmetric models

Abstract We analyze the supersymmetric contributions to B d 0 − B d 0 mixing. For squark and gluino masses which respect the bounds coming from the CERN pp collider, the supersymmetric contribution turns out to be substantially smaller than the corresponding standard model prediction. However, we suggest that the presence of supersymmetry may sizeably contribute to the observability of large CP asymmetries related to the mixing.

NEUTRINO RADIATIVE DECAY IN N=1 SUPERGRAVITY THEORIES

Abstract We show that the supersymmetrization of models where neutrinos acquire mass through the see-saw mechanism allows for tau neutrinos heavier than 15–20 MeV to decay radiatively in a cosmologically safe way (i.e. with a lifetime τ v ⩽5×10 3 s).

Massive Dirac neutrinos, radiative decays and nucleosynthesis

We study the cosmological implications of massive Dirac neutrinos. The conditions for a fast radiative decay, ν → ν′ γ, with the lifetime τ < 5 × 103 s, and the compatibility of three Dirac neutrino species with the predictions of nucleosynthesis are examined. We use a class of E6 superstring-inspired models as a suitable framework for this discussion, where we find that for lepto-quark masses in excess of about 100 GeV, the tau neutrino must weigh less than 50 eV. If ντ is heavy, the above cosmological bounds also lead to possible enhancements of rare processes, such as τ → μγ, B+ → K+ νν and B0 → τμ.