ACP Seminar (Astronomy - Cosmology - Particle Physics)

Speaker: Fanky Wong (U Hong Kong)
Title: Gravitational lensing in a dark matter free braneworld model
Date (JST): Tue, Dec 06, 2011, 15:30 - 16:30
Place: Seminar Room A
Related File: 549.pdf
Abstract: The braneworld model, in which our Universe is a three-brane embedded in a five-dimensional bulk, has attracted a lot of attention recently. The main motivation for the study of the braneworld model comes from the hierarchy problem in particle physics. In the braneworld scenario, in which the extra dimension is not compactified, the four dimensional effective Einstein equation has extra source terms that arise from the em-bedding 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. In the present talk I consider in detail the possibility of testing the hypothesis of dark matter as a bulk effect on the brane through the study of gravitational lensing. The lensing properties of a sample of Low Surface Brightness galaxies, a class of galaxies dominated by their dark matter component, are considered in the framework of the brane world models. Our main result shows that gravitational lensing in the dark matter free braneworld model is different from the standard dark matter models. The presence of the braneworld effects may significantly diminish the photon deflection angle by galaxies. Hence we conclude that the study of the lensing effects of the Low Surface Brightness galaxies could confirm or rule out the braneworld interpretation of dark matter.