Speaker
Dr
Federico URBAN
(Université Libre de Bruxelles)
Description
The Maxwell action is conformally invariant and classically
ignorant of conformally flat metrics. However, if the vector
lives in a disformal metric--- as it does if residing upon a
moving brane---this is no longer true. The disformal
coupling is then mediated by a Dirac-Born-Infeld scalar
field. Here a systematic dynamical system analysis is
developed for anisotropic Bianchi I cosmology with a massive
disformally coupled vector field. Several new fixed points
are found, including anisotropic scaling solutions. The
presented formalism here presented can be conveniently
applied to general scenarios with or without extra
dimensional motivations. This is illustrated here by
performing a complete analysis with simple assumption that
both the potentials and the warp factor for the brane are
(nearly) exponential. In that case, the anisotropic fixed
points are either not attractors, do not describe
accelerating expansion or else they feature too large
anisotropies to be compati
ble with observations. Nonetheless, viable classes of
models exist where isotropy is retained due to rapid
oscillations of the vector field, thus providing a possible
realisation of disformally interacting massive dark matter.