Lower semi-continuity of integrals with G-quasiconvex potential

This paper introduces the proper notion of variational quasiconvexity associated to a group of diffeomorphisms. We prove a lower semicontinuity theorem connected to this notion. In the second part of the paper we apply this result to a class of functions introduced in [5]. Such functions are $GL(n,R)^{+}$ quasiconvex, hence they induce lower semicontinuous integrals.