41 research outputs found
Corpuscular Consideration of Eternal Inflation
We review the paradigm of eternal inflation in the light of the recently
proposed corpuscular picture of space-time. Comparing the strength of the
average fluctuation of the field up its potential with that of quantum
depletion, we show that the latter can be dominant. We then study the full
respective distributions in order to show that the fraction of the space-time
which has an increasing potential is always below the eternal-inflation
threshold. We prove that for monomial potentials eternal inflaton is excluded.
This is likely to hold for other models as well.Comment: 10 pages, 2 figures; revised version to match submitted versio
Uncertainties in primordial black-hole constraints on the primordial power spectrum
The existence (and abundance) of primordial black holes (PBHs) is governed by
the power spectrum of primordial perturbations generated during inflation. So
far no PBHs have been observed, and instead, increasingly stringent bounds on
their existence at different scales have been obtained. Up until recently, this
has been exploited in attempts to constrain parts of the inflationary power
spectrum that are unconstrained by cosmological observations. We first point
out that the simple translation of the PBH non-observation bounds into
constraints on the primordial power spectrum is inaccurate as it fails to
include realistic aspects of PBH formation and evolution. We then demonstrate,
by studying two examples of uncertainties from the effects of critical and
non-spherical collapse, that even though they may seem small, they have
important implications for the usefulness of the constraints. In particular, we
point out that the uncertainty induced by non-spherical collapse may be much
larger than the difference between particular bounds from PBH non-observations
and the general maximum cap stemming from the condition on the
dark-matter density in the form of PBHs. We therefore make the cautious
suggestion of applying only the overall maximum dark-matter constraint to
models of early Universe, as this requirement seems to currently provide a more
reliable constraint, which better reflects our current lack of detailed
knowledge of PBH formation. These, and other effects, such as merging,
clustering and accretion, may also loosen constraints from non-observations of
other primordial compact objects such as ultra-compact minihalos of dark
matter.Comment: 6 pages, 2 figures; v4: revised version to match published versio
Cosmology of the selfaccelerating third order Galileon
In this paper we start from the original formulation of the galileon model
with the original choice for couplings to gravity. Within this framework we
find that there is still a subset of possible Lagrangians that give
selfaccelerating solutions with stable spherically symmetric solutions. This is
a certain constrained subset of the third order galileon which has not been
explored before. We develop and explore the background cosmological evolution
of this model drawing intuition from other even more restricted galileon
models. The numerical results confirm the presence of selfacceleration, but
also reveals a possible instability with respect to galileon perturbations.Comment: 30 pages, 24 figure