Hidden in the background: a local approach to CMB anomalies
  We investigate a framework aiming to provide a common origin for the
large-angle anomalies detected in the Cosmic Microwave Background (CMB), which
are hypothesized as the result of the statistical inhomogeneity developed by
different isocurvature fields of mass $m\sim H$ present during inflation. The
inhomogeneity arises as the combined effect of $(i)$ the initial conditions for
isocurvature fields (obtained after a fast-roll stage finishing many
$e$-foldings before cosmological scales exit the horizon), $(ii)$ their
inflationary fluctuations and $(iii)$ their coupling to other degrees of
freedom. Our case of interest is when these fields (interpreted as the
precursors of large-angle anomalies) leave an observable imprint only in
isolated patches of the Universe. When the latter intersect the last scattering
surface, such imprints arise in the CMB. Nevertheless, due to their
statistically inhomogeneous nature, these imprints are difficult to detect, for
they become hidden in the background similarly to the Cold Spot. We then
compute the probability that a single isocurvature field becomes inhomogeneous
at the end of inflation and find that, if the appropriate conditions are given
(which depend exclusively on the preexisting fast-roll stage), this probability
is at the percent level. Finally, we discuss several mechanisms (including the
curvaton and the inhomogeneous reheating) to investigate whether an initial
statistically inhomogeneous isocurvature field fluctuation might give rise to
some of the observed anomalies. In particular, we focus on the Cold Spot, the
power deficit at low multipoles and the breaking of statistical isotropy.
