Cosmology on a Three-Brane

In this paper a general solution is found for a five dimensional orbifold space-time that induces a k = 0 cosmology on a three-brane. Expressions for the energy density and pressure on the brane in terms of the brane metric are derived. Given a metric on the brane it is possible to find five dimensional space-times that contain the brane. This calculation is carried out for an inflationary universe and for a metric that corresponds to a radiation dominated universe in standard cosmology. It is also shown that any k = 0 cosmology can be embedded in a flat five dimensional orbifold space-time and the equation of the three-brane surface is derived. For an inflationary universe it is shown that the surface is the usual hyperboloid representation of de Sitter space, although it is embedded in an orbifold space-time.