  We study the two-centred AdS_7 x S^4 solution of eleven-dimensional
supergravity using the Euclidean path-integral approach, and find that it can
be interpreted as an instanton, signalling the splitting of the throat of the
M5 brane. The instanton is interpreted as indicating a coherent superposition
of the quantum states corresponding to classically distinct solutions. This is
a surprising result since it leads, through the AdS/CFT correspondence, to
contradictory implications for the dual (2,0) superconformal field theory on
the M5 brane. We also argue that similar instantons should exist for other
branes in ten- and eleven-dimensional supergravity. The counterterm subtraction
technique for gravitational instantons, which arose from the AdS/CFT
correspondence, is examined in terms of its applicability to our results.
Connections are also made to the work of Maldacena et al on anti-de Sitter
fragmentation.
