  Recent experiments on ultracold non-reactive dipolar molecules have observed
high two-body losses, even though these molecules can undergo neither
inelastic, nor reactive (as they are in their absolute ground state), nor
light-assisted collisions (if they are measured in the dark). In the presence
of an electric field these losses seem to be near universal (the probability of
loss at short-range is near unity) while in the absence of it the losses seem
non-universal. To explain these observations we propose a simple model based on
the mixing effect of an electric field on the states of the two diatomic
molecules at long-range and on the density-of-states of the tetramer complex
formed at short-range, believed to be responsible for the losses. We apply our
model to collisions of ground-state molecules of endothermic systems, of
current experimental interest.
