Electron cloud studies for KEKB

Electron-cloud build up, incoherent tune spread and electron-induced beam instability are likely to be responsible for the vertical beam-size increase observed at the KEKB Low Energy Ring (LER). We report on recent simulations and analytical estimated, a ddressing the electron-cloud evolution for various magnet configurations, computing the beam size blow up predicted by three different simulation models (micro-bunches, multiparticle tracking with soft Gaussian approximation, particle-in cell) and finally discussing analytical expressions for the instability threshold.