In my BA thesis  (spanish) I studied the foundations of General Relativity and two important exact solutions: Schwarzschild and Robertson-Walker, the former to model the empty sorroundings of a spherically symmetric object, the latter to describe a Universe with an idealized distribution of mass-energy in an isotropic and homogeneous space.

My MSc thesis  (spanish) was about extending the classical Riemannian concepts of curvature, intinsic and extrinsic, to the more general case of submanifolds embedded in Minkowski space which inherit a metric with changing signature.