Surfaces in Robertson-Walker Space-Times with Positive Relative Nullity

In this article, we study space-like and time-like surfaces in a Robertson-Walker space-time, denoted by L14(f,c), having positive relative nullity. First, we give the necessary and sufficient conditions for such space-like and time-like surfaces in L14(f,c). Then, we obtain the local classification theorems for space-like and time-like surfaces in L14(f,0) with positive relative nullity, where the second factor is 3-dimensional Euclidean space. Finally, we consider the space-like and time-like surfaces in E11×S3 and E11×H3 with positive relative nullity. These are the special spaces of L14(f,c) when the warping function f is a constant function, with c=1 for E11×S3 and c=-1 for E11×H3.