We establish a global existence theory for the equation governing the evolution of a relativistic membrane in a (possibly curved) Lorentzian manifold, when the spacetime metric is a perturbation of the Minkowski metric. Relying on the Hyperboloidal Foliation Method introduced by LeFloch and Ma in 2014, we revisit a theorem established earlier by Lindblad (who treated membranes in the flat Minkowski spacetime) and we provide a simpler proof of existence, which is also valid in a curved spacetime and, most importantly, leads to the important property that the total energy of the membrane is globally bounded in time.
1Our proof uses LeFloch and Ma's Hyperboloidal Foliation Method [15]- [18], which allows one to treat coupled systems of wave and Klein-Gordon equations. This method was built upon earlier work by Klainerman [12] and Hormander [9] on the quasilinear Klein-Gordon equation. The use of the hyperboloidal foliation of Minkowski spacetime to study coupled systems of wave and Klein-Gordon equation was investigated in [15] and several classes of such systems were then treated by this method, including the Einstein equations of general relativity [15,17,18]. Estimates in the hyperboloidal foliation are often more precise and it was observed in [15] that, for certain classes of equations, the energy of the solution is bounded globally in time. See LeFloch-Ma's theorem in [15, Chap. 6]. Our aim in the present paper is to extend this observation to the membrane equation (1.1). Our proof will, in addition, rely on a "double null" property of the membrane equation which was first observed by Lindblad [20].
Statement of the theoremBy the property of finite speed of propagation of the relativistic membranes, we at first specify the domain of the nonvanishing functions, which is the interior of the future light cone from the point (1, 0, 0) K := {(t, x) | r < t − 1}, and the following domain limited by two hyperboloids (with s 0 < s 1 )