E. Massó

Testing the origin of the ΔI = 12 rule through KL dalitz decays

Abstract It is pointed out that the process KrmK L → l + l − γ has some specific properties making it a useful tool to study the structure of the weak non-leptonic interaction. In particular, it is demonstrated how the scheme using penguin diagrams to enhance the K- π transition may experimentally be distinguished from, e.g., Sakurais phenomenological hamiltonian model through a measurement of the ratio Γ (K L → e + e − γ )/ Γ (K L → μ + μ − γ ) .

Limits on the muon and tau neutrino masses from SN1987A

Abstract When neutrinos have a Dirac mass, the right-handed partner can be emitted from the supernova. We calculate the emission rate due to all the important production mechanisms, and use SN1987A data to constrain the neutrino mass. We obtain that m(νμ ⩽ 14 keV and that either m(ντ) ⩾ 34 MeV or m(ντ) ⩽ 14 keV. These limits are reliable within a factor of 3.

Q2 duality and rare pion decays

Abstract Some peculiarities of the π0→e+e− amplitude are discussed. The equivalence between vector meson dominance and quark models is clearly established (Q2 duality). The relevant mass scales in that decay imply some universal properties for the amplitude. The braching ratio B π ≡ Γ(π 0 → e + e − ) Γ(π 0 →γγ) depends only on a characteristic cut-off and not on the details of the models. Our model-insensitive prediction is Bπ∼6×10−8, far below the experimental data.

Radiative and muonic decays of KL. implications for top mass

Abstract We examine the implications for KL phenomenology of the recent experimental determinations of the form factor for the decay KL→e+e−γ. In particular, we reexamine the role of the top quark in light of the new measurements, and we show that for a branching ratio of KL→μ+μ− larger than 1.25 times the unitarty bound, as indicated by one experiment, the top quark mass has to be larger than 115 GeV. We predict a ratio between the rates for KL→e+e−γ and KL→μ+μ−γ of approximately 24.

KL →μ+μ−, top mass and bottom lifetime

Abstract We study a class of diagrams, that has previously been overlooked, contributing to the (dispersive) electromagnetic part of the K L → μ + μ − amplitude. The strength of this extra contribution can be estimated in different models and could be measured in related processes. By combining these results with those coming from the K 0  K 0 transition (evaluated in the Kobayashi-Maskawa scheme) we obtain rather strong constraints on the t quark mass and the B meson lifetime. The recently measured value for the B meson lifetime is difficult to accommodate unless the t quark is very heavy; m t > 100 GeV could be natural values according to the analysis.

Is the δ(980) a broad qq¯qq¯state?

Abstract The conventional (qq¯) or unconventional (qq¯qq¯) interpretation of the scalar δ(980) meson is reconsidered by analyzing a series of processes (η′→ηππdecay, D,E→δπ decays and δ 0- tadpole contributions to e.m. mass-mixing) which are sensitive to these alternative interpretations. A conventional (qq¯) nature for the δ(980) turns out to be preferred in all the cases.

Scaling violation in γγ scattering

An unorthodox model is examined which predicts that scaling violations in structure functions are related to properties of the photon vacuum polarization amplitude. The relationship is approximate, but very useful. It reproduces the leading QCD prediction in all cases, and allows, as for instance in γγ scattering, to fill up on what QCD cannot say by itself. There is a simple formula for the total γγ cross-section, valid for all values of the photon mass. Data frome+ e− annihilation can be fed into it to obtain a fit to the measured photon structure function. The PLUTO data are not all difficult to reproduce.

The total γγ cross-section for allQ2

The total cross-section for the production of hadrons in γγ scattering, and its breakdown into flavour contributions are calculated as a function of the invariant mass of one of the photons, the other being on-shell, in a vector meson dominance model. Knowledge of the vector meson mass spectrum is not required, although when available it may be used to further check the over-all consistency of the model. The predicted cross-section is compared with data from PETRA.

The

The rare π 0 → e + e + and η → μ + m − decays are calculated in different schemes, which are seen to be essentially equivalent to and produce the same results as conventional vector-meson dominance. We obtain the theoretical predictions B(π 0 → e + e − ) = (6.41 ± 0.19) × 10 −8 and B(η → μ + m − ) = (1.14 −0.03 +0.07 ) × 10 −5 , where B(P → l + l − ) = Γ(P → l + l − )/Γ(P → γγ), in reasonable agreement with recent experimental dataThe rare

\pi^0\to e^+e^-

\pi^0 \to e^+e^-