4 research outputs found
Production and dilution of gravitinos by modulus decay
We study the cosmological consequences of generic scalar fields like moduli
which decay only through gravitationally suppressed interactions. We consider a
new production mechanism of gravitinos from moduli decay, which might be more
effective than previously known mechanisms, and calculate the final
gravitino-to-entropy ratio to compare with the constraints imposed by
successful big bang nucleosynthesis (BBN) etc., taking possible hadronic decays
of gravitinos into account. We find the modulus mass smaller than
TeV is excluded. On the other hand, inflation models with high reheating
temperatures GeV can be compatible with BBN thanks
to the late-time entropy production from the moduli decay if model parameters
are appropriately chosen.Comment: 18 pages, 4 figures, to appear in Phys. Rev.
Quintessential Kination and Cold Dark Matter Abundance
The generation of a kination-dominated phase by a quintessential exponential
model is investigated and the parameters of the model are restricted so that a
number of observational constraints (originating from nucleosynthesis, the
present acceleration of the universe and the dark-energy-density parameter) are
satisfied. The decoupling of a thermal cold dark matter particle during the
period of kination is analyzed, the relic density is calculated both
numerically and semi-analytically and the results are compared with each other.
It is argued that the enhancement, with respect to the standard paradigm, of
the cold dark matter abundance can be expressed as a function of the
quintessential density parameter at the onset of nucleosynthesis. We find that
values of the latter quantity close to its upper bound require the
thermal-averaged cross section times the velocity of the cold relic to be
almost three orders of magnitude larger than this needed in the standard
scenario so as compatibility with the cold dark matter constraint is achieved.Comment: Published versio
Single-field inflation, anomalous enhancement of superhorizon fluctuations, and non-Gaussianity in primordial black hole formation
We show a text-book potential for single-field inflation, namely, the
Coleman-Weinberg model can induce double inflation and formation of primordial
black holes (PBHs), because fluctuations that leave the horizon near the end of
first inflation are anomalously enhanced at the onset of second inflation when
the time-dependent mode turns to a growing mode rather than a decaying mode.
The mass of PBHs produced in this mechanism lies in several discrete ranges
depending on the model parameters. We also calculate the effects of
non-Gaussian statistics due to higher-order interactions on the abundance of
PBHs, which turns out to be small.Comment: 22pages, 8figure