
In this paper under review, the author proves a Dirichlet problem for space-like hypersurfaces with prescribed scalar curvature in Minkowski space. Let \({\mathbb R}^{n,1}\) be the Minkowski space \(\displaystyle{{\mathbb R}^{n,1} = \bigl({\mathbb R}^{n+1}, \sum_{i=1}^n dx_i^2 - dx_{n+1}^2 \bigr)}\) with the canonical coordinates \((x_1, \dots, x_{n+1})\). Let \(\Omega\) be a smooth bounded domain in \({\mathbb R}^{n}= \{x_{n+1} = 0\}\) and let \(u\) be a smooth function defined on \(\overline{\Omega}\) satisfying \(\displaystyle{\sup_{\overline{\Omega}} | Du| 0\quad(1\leq k\leq m). \] The author proves if \(\Omega\) is a smooth bounded domain in \({\mathbb R}^3\) and strictly convex, and \(H\) a smooth positive function on \(\overline{\Omega}\), then given a spacelike function \(\varphi\) which is strictly convex, the following Dirichlet problem \[ \left\{ \begin{aligned} {\mathcal H}_2[u] &= H \quad \text{in}\quad \Omega\\ u&=\varphi\quad \text{on}\quad \partial \Omega \end{aligned} \right. \] has a unique solution. In case \({\mathbb R}^4\), the author also shows that if \(H\) is constant, then the Dirichlet problem is also uniquely solvable. The proof relies on a standard continuity method which reduces it to a priori \(C^1\)- and \(C^2\)-estimates. These estimates imply \({\mathcal H}_m\) is uniformly elliptic. The author shows two types of \(C^2\)-estimates, i.e., normal second derivatives estimates and mixed (tangential-normal) second derivatives estimates on the boundary. And the maximum principle is also needed to complete the proof of the main result. The dimension restriction, \(n=3\) or \(n=4\) and \(m=2\), follows from the maximum principle and normal second derivatives estimates, whereas the \(C^1\) global estimate and the tangential-normal second derivatives estimate on the boundary can be obtained without any dimension restriction. The author also conjectures that such a Dirichlet problem might be always solvable in any dimension \(n\) and any \(m\) if \(\Omega\) is a smooth convex bounded domain which has at least \(m-1\) positive principal curvatures at every boundary point.
Global differential geometry of Lorentz manifolds, manifolds with indefinite metrics, Nonlinear boundary value problems for linear elliptic equations, scalar curvature, Mikowski space, Methods of global Riemannian geometry, including PDE methods; curvature restrictions, spacelike hypersurface, Dirichlet problem
Global differential geometry of Lorentz manifolds, manifolds with indefinite metrics, Nonlinear boundary value problems for linear elliptic equations, scalar curvature, Mikowski space, Methods of global Riemannian geometry, including PDE methods; curvature restrictions, spacelike hypersurface, Dirichlet problem
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