148 research outputs found
Can massive primordial black holes be produced in mild waterfall hybrid inflation?
We studied the possibility whether the massive primordial black holes (PBHs)
surviving today can be produced in hybrid inflation. Though it is of great
interest since such PBHs can be the candidate for dark matter or seeds of the
supermassive black holes in galaxies, there have not been quantitatively
complete works yet because of the non-perturbative behavior around the critical
point of hybrid inflation. Therefore, combining the stochastic and
formalism, we numerically calculated the curvature perturbations in a
non-perturbative way and found, without any specific assumption of the types of
hybrid inflation, PBHs are rather overproduced when the waterfall phase of
hybrid inflation continues so long that the PBH scale is well enlarged and the
corresponding PBH mass becomes sizable enough.Comment: 1+19 pages, 5 figures, JCAP accepted version with updated figure
Squeezed Bispectrum in the Formalism: Local Observer Effect in Field Space
The prospects of future galaxy surveys for non-Gaussianity measurements call
for the development of robust techniques for computing the bispectrum of
primordial cosmological perturbations. In this paper, we propose a novel
approach to the calculation of the squeezed bispectrum in multiple-field
inflation. With use of the formalism, our framework sheds new light
on the recently pointed out difference between the squeezed bispectrum for
global observers and that for local observers, while allowing one to calculate
both. For local observers in particular, the squeezed bispectrum is found to
vanish in single-field inflation. Furthermore, our framework allows one to go
beyond the near-equilateral ("small hierarchy") limit, and to automatically
include intrinsic non-Gaussianities that do not need to be calculated
separately. The explicit computational programme of our method is given and
illustrated with a few examples.Comment: 1+33 pages, 6 figures, matches published version in JCA
Does the detection of primordial gravitational waves exclude low energy inflation?
We show that a detectable tensor-to-scalar ratio on the CMB
scale can be generated even during extremely low energy inflation which
saturates the BBN bound . The source of
the gravitational waves is not quantum fluctuations of graviton but those of
gauge fields, energetically supported by coupled axion fields. The
curvature perturbation, the backreaction effect and the validity of
perturbative treatment are carefully checked. Our result indicates that
measuring alone does not immediately fix the inflationary energy scale.Comment: 6 pages, 3 figure
Stochastic dynamics of multi-waterfall hybrid inflation and formation of primordial black holes
We show that a hybrid inflation model with multiple waterfall fields can
result in the formation of primordial black hole (PBH) with an astrophysical
size, by using an advanced algorithm to follow the stochastic dynamics of the
waterfall fields. This is in contrast to the case with a single waterfall
field, where the wavelength of density perturbations is usually too short to
form PBHs of the astrophysical scale (or otherwise PBH are overproduced and the
model is ruled out) unless the inflaton potential is tuned. In particular, we
demonstrate that PBHs with masses of order can form after
hybrid inflation consistently with other cosmological observations if the
number of waterfall fields is about 5 for the case of instantaneous reheating.
Observable gravitational waves are produced from the second-order effect of
large curvature perturbations as well as from the dynamics of texture or global
defects that form after the waterfall phase transition.Comment: 23 pages, 5 figure
On the primordial black hole formation in hybrid inflation
We revisit the scenario of primordial black hole (PBH) formation from large
curvature perturbations generated during the waterfall phase transition in
hybrid inflation models. In a minimal setup considered in the literature, the
mass and abundance of PBHs are correlated and astrophysical size PBHs tend to
be overproduced. This is because a longer length scale for curvature
perturbations (or a larger PBH mass) requires a longer waterfall regime with a
flatter potential, which results in overproduction of curvature perturbations.
However, in this paper, we discuss that the higher-dimensional terms for the
inflaton potential affect the dynamics during the waterfall phase transition
and show that astrophysical size PHBs of order
(which can explain the whole dark matter) can form in some parameter space
consistently with any existing constraints. The scenario can be tested by
observing the induced gravitational waves from scalar perturbations by future
gravitational wave experiments, such as LISA.Comment: 14 pages, 8 figures; v2: minor corrections, figures updated,
conclusions unchange
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