  In the LHC, a transverse instability is regularly observed at 4TeV right
after the beta-squeeze, when the beams are separated by about their ten
transverse rms sizes [1-3], and only one of the two beams is seen as
oscillating. So far only a single hypothesis is consistent with all the
observations and basic concepts, one about a third beam - an electron cloud,
generated by the two proton beams in the high-beta areas of the interaction
regions.
