144 research outputs found
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
Squeezed bispectrum and one-loop corrections in transient constant-roll inflation
In canonical single-field inflation, the production of primordial black holes
(PBH) requires a transient violation of the slow-roll condition. The transient
ultra slow-roll inflation is an example of such scenario, and more generally,
one can consider the transient constant-roll inflation. We investigate the
squeezed bispectrum in the transient constant-roll inflation, and find that the
Maldacena's consistency relation holds for a sufficiently long-wavelength mode,
whereas it is violated for modes around the peak scale for the non-attractor
case. We also demonstrate how the one-loop corrections are modified compared to
the case of the transient ultra slow-roll inflation, focusing on representative
one-loop terms orgiginating from a time derivative of the second slow-roll
parameter in the cubic action. We find that the perturbativity requirement on
those terms does not rule out the production of PBH from the transient
constant-roll inflation. Therefore, it is a simple counterexample of the
recently claimed no-go theorem of PBH production from single-field inflation.Comment: 26 pages, 14 figure
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