X iv : a st ro - p h / 04 07 22 2 v 2 1 3 Ju l 2 00 4 Einstein - Rosen Bridges and the Characteristic Properties

ar X iv : a st ro - p h / 04 07 23 2 v 1 1 2 Ju l 2 00 4 B The Saas Fee Lectures on Strong Gravitational Lensing

ar X iv : a st ro - p h / 04 08 01 0 v 1 3 1 Ju l 2 00 4 On the nature of the unidentified X - ray / γ - ray sources

We present a multiwavelength study of the environment of the unidentified X-ray/γ-ray sources IGR J18027−1455 and IGR J21247+5058, recently discovered by the IBIS/ISGRI instrument, onboard the INTEGRAL satellite. The main properties of the sources found inside their position error circles, give us clues about the nature of these high-energy sources.

ar X iv : a st ro - p h / 04 06 56 7 v 1 2 4 Ju n 20 04 1

ar X iv : a st ro - p h / 05 05 09 6 v 2 2 3 Ju l 2 00 5 1 Curvature driven acceleration : a utopia or a reality ?

The present work shows that a combination of nonlinear contributions from the Ricci curvature in Einstein field equations can drive a late time acceleration of expansion of the universe. The transit from the decelerated to the accelerated phase of expansion takes place smoothly without having to resort to a study of asymptotic behaviour. This result emphasizes the need for thorough and critical...

X iv : a st ro - p h / 04 07 31 1 v 1 1 5 Ju l 2 00 4 Ultrahigh Energy Cosmic Rays : Old Physics or New Physics ?

We consider the advantages of and the problems associated with hypotheses to explain the origin of ultrahigh energy cosmic rays (UHECR: E > 10 EeV) and the " trans-GZK " cosmic rays (TGZK: E > 100 EeV) both through " old physics " (acceleration in cosmic sources) and " new physics " (new particles, topological defects, fat neutrino cross sections, Lorentz invariance violation).