  Versions of M-theory are found in spacetime signatures (9,2) and (6,5), in
addition to the usual M-theory in 10+1 dimensions, and these give rise to type
IIA string theories in 10-dimensional spacetime signatures
(10,0),(9,1),(8,2),(6,4) and (5,5), and to type IIB string theories in
signatures (9,1),(7,3) and (5,5). The field theory limits are
  10 and 11 dimensional supergravities in these signatures. These theories are
all linked by duality transformations which can change the number of time
dimensions as well as the number of space dimensions, so that each should be a
different limit of the same underlying theory.
