Anisotropy dissipation in brane-world inflation

We examine the behavior of an anisotropic brane-world in the presence of inflationary scalar fields. We show that, contrary to naive expectations, a large anisotropy does not adversely affect inflation. On the contrary, a large initial anisotropy introduces more damping into the scalar field equation of motion, resulting in greater inflation. The rapid decay of anisotropy in the brane-world significantly increases the class of initial conditions from which the observed universe could have originated. This generalizes a similar result in general relativity. A unique feature of Bianchi type I brane-world cosmology appears to be that for scalar fields with a large kinetic term the initial expansion of the Universe is quasi-isotropic. The Universe grows more anisotropic during an intermediate transient regime until anisotropy finally disappears during inflationary expansion.