Galactic Metric, Dark Radiation, Dark Pressure, and Gravitational Lensing in Brane World Models

In the braneworld scenario, the four dimensional effective Einstein equation has extra terms which arise from the embedding of the 3-brane in the bulk. These non-local effects, generated by the free gravitational field of the bulk, may provide an explanation for the dynamics of the neutral hydrogen clouds at large distances from the galactic center, which is usually explained by postulating the existence of the dark matter. We obtain the exact galactic metric, the dark radiation and the dark pressure in the flat rotation curves region in the brane world scenario. Due to the presence of the bulk effects, the flat rotation curves could extend several hundred kpc. The limiting radius for which bulk effects are important is estimated and compared with the numerical values of the truncation parameter of the dark matter halos, obtained from weak lensing observations. There is a relatively good agreement between the predictions of the model and observations. The deflection of photons is also considered and the bending angle of light is computed. The bending angle predicted by the brane world models is much larger than that predicted by standard general relativistic and dark matter models. The angular radii of the Einstein rings are obtained in the small angles approximation. The predictions of the brane world model for the tangential shear are compared with the observational data obtained in the weak lensing of galaxies in the Red-Sequence Cluster Survey. Therefore the study of the light deflection by galaxies and the gravitational lensing could discriminate between the different dynamical laws proposed to model the motion of particles at the galactic level and the standard dark matter models.