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| | Compact pseudo-Riemannian manifolds with parallel Weyl tensor | Department of Mathematics |
 | | A pseudo-Riemannian manifold (M,g) of dimension n > 3 which is neither conformally flat nor locally symmetric, such that the Weyl conformal tensor of g is parallel, is called an ECS manifold (short for "essentially conformally symmetric"). |
 | | The ECS manifolds shown to exist are nontrivial torus bundles over the circle, and arise from a construction that a priori yields bundles over the circle, having as the fibre either a torus, or a 2-step nilmanifold with a complete flat torsionfree connection; our argument only realizes the torus case. |
 | | Namely, every compact ECS manifold has an infinite fundamental group, its Euler characteristic is zero, and its real Pontryagin classes all vanish; for any compact ECS Lorentzian manifold (M,g), some two-fold covering manifold of M is a bundle over the circle; and, finally, every four-dimensional ECS Lorentzian manifold is noncompact. |
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