This article synthesises and extends recent work on the cosmological
consequences of dropping the usual Z_2 reflection symmetry postulate in brane
world scenarios. It is observed that for a cosmological model of homogeneous
isotropic type, the relevant generalised Birkhoff theorem establishing
staticity of the external vacuum in the maximally symmetric ``bulk'' outside a
freely moving world brane will remain valid for the case of motion that is
forced by minimal (generalised Wess Zumino type) coupling to an external
antisymmetric gauge field provided its kinetic action contribution has the
usual homogeneous quadratic form. This means that the geometry on each side of
the brane worldsheet will still be of the generalised Schwarzschild anti de
Sitter type. The usual first integrated Friedmann equation for the Hubble
expansion rate can thereby be straightforwardly generalised by inclusion of new
terms involving 2 extra parameters respectively measuring the strength of the
gauge coupling and the degree of deviation from reflection symmetry. Some
conceivable phenomenological implications are briefly outlined, and
corresponding limitations are derived for possible values of relevant
parameters.Comment: 13 pages latex (revised to rectify a couple of sign transcription
errors
