We study some Weingarten spacelike hypersurfaces in a de Sitter space S 1 (1). If the Weingarten spacelike hypersurfaces have two distinct principal curvatures, we obtain two classification theorems which give some characterization of the Riemannian product H(1−coth ̺)× S(1 − tanh ̺), 1 < k < n − 1 in S 1 (1), the hyperbolic cylinder H(1 − coth ̺) × S(1 − tanh ̺) or spherical cylinder H(1 − coth ̺)×...

We construct an eternally inflating spacelike brane world model. This model is feasible only if the space dimension of the brane is three (SM2) or six (SM5) for M theory or four (SD3) for superstring theory. A time-dependent n-form field would supply a constant energy density and cause eternal expansion of the spacelike brane. On the other hand, the hyperbolic space perpendicular to the brane w...

We construct an eternally inflating spacelike brane world model. If the space dimension of the brane is three (SM2) or six (SM5) for M theory or four (SD3) for superstring theory, a time-dependent n-form field would supply a constant energy density and cause exponentially expansion of the spacelike brane. In these cases, the hyperbolic space perpendicular to the brane would keep its scale facto...

We revisit the question of microcausality violations in quantum field theory on noncommutative spacetime, taking O(x) =: φ⋆φ : (x) as a sample observable. Using methods of the theory of distributions, we precisely describe the support properties of the commutator [O(x),O(y)] and prove that, in the case of spacespace noncommutativity, it does not vanish at spacelike separation in the noncommutin...

In nonrelativistic quantum mechanics, measurements performed by separate observers are modeled via tensor products. In algebraic quantum field theory, though, local observables corresponding to spacelike separated parties are just required to commute. The problem of determining whether these two definitions of separation lead to the same set of bipartite correlations is known in nonlocality as ...

The classical Avez-Seifert theorem is generalized to the case of the Lorentz force equation for charged test particles with fixed charge-to-mass ratio. Given two events x0 and x1, with x1 in the chronological future of x0, and a ratio q/m, it is proved that a timelike connecting solution of the Lorentz force equation exists provided there is no null connecting geodesic and the spacetime is glob...

We investigate the problem of the stability of the number of conjugate or focal points (counted with multiplicity) along a semi-Riemannian geodesic γ. For a Riemannian or a non spacelike Lorentzian geodesic, such number is equal to the intersection number (Maslov index) of a continuous curve with a subvariety of codimension one of the Lagrangian Grassmannian of a symplectic space. Such intersec...