"La aparición de singularidades, la no definición de un tensor para la energía del campo gravitatorio, la causa de la expansión acelerada del universo y la explicación con la materia oscura de las curvas de rotación de ...

The purpose of this paper is to prove a Hitchin–Thorpe inequality for a four-dimensional compact almost Ricci soliton. Moreover, we prove that under a suitable integral condition, a four-dimensional compact almost Ricci ...

Consideramos o espaço pseudo-Euclidiano (Rn, g), com coordenadas x = (x1, ..., xn), n _ 3, e gij = _ij"i, "i = ±1. Seja T um tensor simétrico de ordem 2, definido por T = nXi,j=1 "jFij(xk)dxi dxj , onde k ´e fixo, "jFij(xk) ...

Type A surfaces are the locally homogeneous affine surfaces which can be locally described by constant Christoffel symbols. We address the issue of the geodesic completeness of these surfaces: we show that some models for ...