Nonexistence and umbilicity of spacelike submanifolds with second fundamental form locally timelike

Under the assumption that the second fundamental form is locally timelike, we establish new nonexistence and umbilicity results concerning n-dimensional spacelike submanifolds immersed with parallel mean curvature vector in the (n+p)-dimensional de Sitter space S-q(n+p) of index q, such that 1 <= q <= p.Our approach is based on a Simon's type inequality involving the norm of the total umbilicity tensor, obtained by Mariano in [17], jointly with suitable maximum principles due to Alias, Caminha and do Nascimento [6, 7] for complete noncompact Riemannian manifolds and a weak version of Omori-Yau's maximum principle for stochastically complete Riemanian manifolds proved by Pigola, Rigoli and Setti [20, 21].