Anisotropic power-law inflation for the Dirac-Born-Infeld theory

We find a new set of the Bianchi type I power-law expanding solutions in a string-motivated Dirac-Born-Infeld theory. Stability analysis shows that these power-law inflationary solutions remain stable with or without the contribution of the Dirac-Born-Infeld effect. We also find a new set of Bianchi type I expanding power-law solutions in a two scalar Dirac-Born-Infeld model with an additional phantom field. It is shown that the inclusion of the phantom field turns the Bianchi type I power-law solutions unstable during the inflationary phase.