We study bipartite entanglement in systems of N identical bosons distributed
in M different modes. For such systems, a definition of separability not
related to any a priori Hilbert space tensor product structure is needed and
can be given in terms of commuting subalgebras of observables. Using this
generalized notion of separability, we classify the states for which partial
transposition turns out to be a necessary and sufficient condition for
entanglement detection.Comment: LaTeX, 22 page
