An anisotropic universe due to dimension-changing vacuum decay
  In this paper we consider the question of observational signatures of a false
vacuum decay event in the early universe followed by a period of inflation; in
particular, motivated by the string landscape, we consider decays in which the
parent vacuum has a smaller number of large dimensions than the current vacuum,
which leads to an anisotropic universe. We go beyond previous studies, and
examine the effects on the CMB temperature and polarisation power spectra, due
to both scalar and tensor modes, and consider not only late-time effects but
also the full cosmological perturbation theory at early times. We find that
whilst the scalar mode behaves as one would expect, and the effects of
anisotropy at early times are sub-dominant to the late-time effects already
studied, for the tensor modes in fact the the early-time effects grow with
multipole and can become much larger than one would expect, even dominating
over the late-time effects. Thus these effects should be included if one is
looking for such a signal in the tensor modes.
