TREE-LEVEL LONG-DISTANCE CONTRIBUTIONS TO K+→π+ ℓ+ℓ-

We study a new contribution, which is a tree-level transition from long-distance dynamics, to K+→π+ℓ+ℓ- (ℓ = e, μ) decays. It is found that this tree-diagram can be calculated unambiguously and would generate the additional contribution to the vector, axial-vector, scalar and pseudoscalar form factor of the decay. Our analysis shows that these form factors are strongly suppressed and this long-distance contribution is well under control.

THE STRANGENESS CHANGING ANTINEUTRINO REACTION ${\bar\nu}_L+P\longrightarrow\Lambda+L^+$

We obtain the cross sections for the reactions [Formula: see text] where L is a massive lepton, i.e. a muon or a tau lepton. We do this from near threshold to relativistic energies. We further obtain the contributions of various form factors and interference terms to the cross section with a view to discovering if the contributions from hard to observe form factors such as the weak pseudoscalar form factor, FP, and the weak electric form factor, FE might be obtained via these reactions. The form factor FE is particularly interesting as in the more usually observed p↔n transition it is a second class current and forbidden by G-parity. However in the p↔Λ transition it is not forbidden and it would be desirable to learn if it is present. Finally we discuss our results and prospects for these experiments.