The metric and strong coupling limit of the M5-brane

We find the analog of the Boillat metric of Born-Infeld theory for the M5-b rane. We show that it provides the propagation cone of all 5-brane degrees. In an arbitrary background field, this cone never lies outside the Einstei n cone. An energy momentum tensor for the three-form is defined and shown t o satisfy the Dominant Energy Condition. The theory is shown to be well def ined for all values of the magnetic field but there is a limiting electric field strength. We consider the strong coupling limit of the M5-brane and s how that the corresponding theory is conformally invariant and admits infin itely many conservation laws. On reduction to the Born-Infeld case this agr ees with the work of Bialynicki-Birula. (C) 2001 American Institute of Phys ics.