862 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
Late-time Affleck-Dine baryogenesis after thermal inflation
Thermal inflation can solve serious cosmological problems such as
overproduction of gravitinos and moduli. However, it also dilutes the
preexisting baryon asymmetry. We investigate a possibility that Affleck-Dine
mechanism works after thermal inflation and generate the baryon number at an
acceptable level using lattice calculation. We find that a proper amount of
baryon number can be generated for appropriate model parameters.Comment: 6 pages, 5 figures, reference adde
Gravitino dark matter and baryon asymmetry from Q-ball decay in gauge mediation
We investigate the Q-ball decay in the gauge-mediated SUSY breaking. Q balls
decay mainly into nucleons, and partially into gravitinos, while they are
kinematically forbidden to decay into sparticles which would be cosmologically
harmful. This is achieved by the Q-ball charge small enough to be unstable for
the decay, and large enough to be protected kinematically from unwanted decay
channel. We can then have right amounts of the baryon asymmetry and the dark
matter of the universe, evading any astrophysical and cosmological
observational constraints such as the big bang nucleosynthesis, which has not
been treated properly in the literatures.Comment: 7 pages, 6 eps figures, footnote adde
Comments on the Evolution of Strongly Degenerate Neutrinos in the Early Universe
We reconsider the evolution of strongly degenerate neutrinos in the early
universe. Our chief concern is the validity of the entropy conservation after
the neutrino annihilation process has frozen out (so that the establishment of
chemical equilibrium is not trivial). We argue that the entropy indeed
conserves because elastic scattering keeps the neutrino and antineutrino
distribution functions in the equilibrium form and the sum of their chemical
potential keeps zero even after the neutrino annihilation freeze-out. We also
simulate the evolution of the degenerate neutrino spectrum to support the
argument. We conclude that the change in the neutrino degeneracy parameter when
the relativistic degrees of freedom in the universe decreases is calculated
using the entropy conservation and the lepton number conservation without
worrying about at what temperature the neutrino annihilation process freezes
out.Comment: 12 pages, 3 figure
QCD axion dark matter from long-lived domain walls during matter domination
The domain wall problem of the Peccei-Quinn mechanism can be solved if the
Peccei-Quinn symmetry is explicitly broken by a small amount. Domain walls
decay into axions, which may account for dark matter of the universe. This
scheme is however strongly constrained by overproduction of axions unless the
phase of the explicit breaking term is tuned. We investigate the case where the
universe is matter-dominated around the temperature of the MeV scale and domain
walls decay during this matter dominated epoch. We show how the viable
parameter space is expanded.Comment: 13 pages, 2 figure
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