Quasiconvexity and Lower Semicontinuity in the Riemannian Setting

Abstract

We introduce a notion of quasiconvexity for integrands defined on the bundle of linear maps between the tangent spaces of two smooth, connected and complete Riemannian manifolds $(M,g)$ and $(N,h)$, naturally extending the classical Euclidean notion. For continuous integrands, we prove that this Riemannian quasiconvexity is equivalent to the sequential lower semicontinuity of the associated functional $$F(u,\Omega )={\int }_{\Omega }f(du)d{\mu }_g$$ with respect to the weak${}^{\ast }$ convergence in $W^{1,\infty }(\Omega ,N)$, in the intrinsic sense adopted in the paper, for every bounded open subset $\Omega \subseteq M$. We then establish the Riemannian analogues of the Acerbi--Fusco theorems for Carathéodory integrands satisfying the corresponding growth conditions, for every $1⩽p⩽+\infty$, with respect to the weak and weak${}^{\ast }$ notions of convergence considered here.