Weyl fluid dark matter model tested on the galactic scale by weak gravitational lensing

Abstract: The higher dimensional Weyl curvature induces on the brane a new source of gravity. This Weyl fluid of geometrical origin (reducing in the spherically symmetric, static configuration to a dark radiation and dark pressure) modifies space-time geometry around galaxies and has been shown to explain the flatness of galactic rotation curves. Independent observations for discerning between the Weyl fluid and other dark matter models are necessary. Gravitational lensing could provide such a test. Therefore we study null geodesics and weak gravitational lensing in the dark radiation dominated region of galaxies in a class of spherically symmetric brane-world metrics. We find that the lensing profile in the brane-world scenario is distinguishable from dark matter lensing, despite both the brane-world scenario and dark matter models fitting the rotation curve data. In particular, in the asymptotic regions light deflection is 18% enhanced as compared to dark matter halo predictions. For a linear equation of state of the Weyl fluid we further find a critical radius, below which brane-world effects reduce, while above it they amplify light deflection. This is in contrast to any dark matter model, the addition of which always increases the deflection angle.