The metric and strong coupling limit of the M5-brane

Abstract
We find the analog of the Boillat metric of Born–Infeld theory for the M5-brane. We show that it provides the propagation cone of all 5-brane degrees. In an arbitrary background field, this cone never lies outside the Einstein cone. An energy momentum tensor for the three-form is defined and shown to satisfy the Dominant Energy Condition. The theory is shown to be well defined 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 show that the corresponding theory is conformally invariant and admits infinitely many conservation laws. On reduction to the Born–Infeld case this agrees with the work of Białynicki-Birula.