Large-scale inhomogeneity of dark energy produced in the ancestor vacuum
  We investigate large-scale inhomogeneity of dark energy in the bubble
nucleation scenario of the universe. In this scenario, the present universe was
created by a bubble nucleation due to quantum tunneling from a metastable
ancestor vacuum, followed by a primordial inflationary era. During the bubble
nucleation, supercurvature modes of some kind of a scalar field are produced,
and remain until present without decaying; thus they can play a role of the
dark energy, if the mass of the scalar field is sufficiently light in the
present universe. The supercurvature modes fluctuate at a very large spatial
scale, much longer than the Hubble length in the present universe. Thus they
create large-scale inhomogeneities of the dark energy, and generate large-scale
anisotropies in the cosmic microwave background (CMB) fluctuations. This is a
notable feature of this scenario, where quantum fluctuations of a scalar field
are responsible for the dark energy. In this paper, we calculate imprints of
the scenario on the CMB anisotropies through the integrated Sachs-Wolfe (ISW)
effect, and give observational constraints on the curvature parameter
$\Omega_K$ and on an additional parameter $\epsilon$ describing some properties
of the ancestor vacuum.
