SUPERSYMMETRIC PREDICTION FOR THE MUON TRANSVERSE POLARIZATION IN THEK-]PI(0)MU(+)NU(MU) DECAY()

The muon transverse polarization in the K+ --> pi(0) mu(+) nu(mu) deca y will be measured at the 10(-4) level in forthcoming experiments. We compare the phenomenological perspectives with the theoretical predict ions in supersymmetric extensions of the standard model. In the minima l extension, CP-violating phases lead to a nonzero transverse polariza tion, that, however, is too small to account for a positive experiment al signal. The problems that one encounters when departing from minima l assumptions are discussed. An observable effect is possible if the h ypothesis of R-parity conservation is relaxed, but only at the price o f assuming a very special pattern for the R-parity-breaking couplings.