678 research outputs found
Cosmological Moduli Problem and Thermal Inflation Models
In superstring theories, there exist various dilaton and modulus fields which
masses are expected to be of the order of the gravitino mass . These
fields lead to serious cosmological difficulties, so called ``cosmological
moduli problem'', because a large number of moduli particles are produced as
the coherent oscillations after the primordial inflation. We make a
comprehensive study whether the thermal inflation can solve the cosmological
moduli problem in the whole modulus mass region
predicted by both hidden sector supersymmetry (SUSY) breaking and
gauge-mediated SUSY breaking models. In particular, we take into account the
primordial inflation model whose reheating temperature is so low that its
reheating process finishes after the thermal inflation ends. We find that the
above mass region survives from
various cosmological constraints in the presence of the thermal inflation.Comment: 49 pages, 17 figure
Hadronic Axion Model in Gauge-Mediated Supersymmetry Breaking and Cosmology of Saxion
Recently we have proposed a simple hadronic axion model within gauge-mediated
supersymmetry breaking. In this paper we discuss various cosmological
consequences of the model in great detail. A particular attention is paid to a
saxion, a scalar partner of an axion, which is produced as a coherent
oscillation in the early universe. We show that our model is cosmologically
viable, if the reheating temperature of inflation is sufficiently low. We also
discuss the late decay of the saxion which gives a preferable power spectrum of
the density fluctuation in the standard cold dark matter model when compared
with the observation.Comment: 24 pages, 3 figure
The masses of active neutrinos in the nuMSM from X-ray astronomy
In an extention of the Standard Model by three relatively light right-handed
neutrinos (the nuMSM model) the role of the dark matter particle is played by
the lightest sterile neutrino. We demonstrate that the observations of the
extragalactic X-ray background allow to put a strong upper bound on the mass of
the lightest active neutrino and predict the absolute values of the mass of the
two heavier active neutrinos in the nuMSM, provided that the mass of the dark
matter sterile neutrino is larger than 1.8 keV.Comment: 6 pages. revtex
On the Moduli Problem and Baryogenesis in Gauge-mediated SUSY Breaking Models
We investigate whether the Affleck-Dine mechanism can produce sufficient
baryon number of the universe in the gauge-mediated SUSY breaking models, while
evading the cosmological moduli problem by late-time entropy production. We
find that the Q-ball formation renders the scenario very difficult to work,
irrespective of the detail mechanism of the entropy production.Comment: 11 pages, RevTeX, 5 postscript figures include
Reheating-temperature independence of cosmological baryon asymmetry in Affleck-Dine leptogenesis
In this paper we point out that the cosmological baryon asymmetry in our
universe is generated almost independently of the reheating temperature
in Affleck-Dine leptogenesis and it is determined mainly by the mass of the
lightest neutrino, , in a wide range of the reheating temperature
-- GeV. The present baryon asymmetry predicts the
in a narrow region, -- eV.
Such a small mass of the lightest neutrino leads to a high predictability on
the mass parameter contributing to the neutrinoless double
beta decay. We also propose an explicit model in which such an ultralight
neutrino can be naturally obtained.Comment: 22 pages, LaTeX, 9 eps figure
Where to find a dark matter sterile neutrino?
We propose a strategy of how to look for dark matter (DM) particles
possessing a radiative decay channel and derive constraints on their parameters
from observations of X-rays from our own Galaxy and its dwarf satellites. When
applied to the sterile neutrinos in keV mass range, it allows a significant
improvement of restrictions to its parameters, as compared with previous works.Comment: 5 pp, revtex; v3: 1-sigma limits have been replaced by more
conservative 3-sigma limits, a picture illustrating the data analysis methods
has been ade
Leptogenesis from -dominated early universe
We investigate in detail the leptogenesis by the decay of coherent
right-handed sneutrino having dominated the energy density of
the early universe, which was originally proposed by HM and TY. Once the
dominant universe is realized, the amount of the generated
lepton asymmetry (and hence baryon asymmetry) is determined only by the
properties of the right-handed neutrino, regardless of the history before it
dominates the universe. Moreover, thanks to the entropy production by the decay
of the right-handed sneutrino, thermally produced relics are sufficiently
diluted. In particular, the cosmological gravitino problem can be avoided even
when the reheating temperature of the inflation is higher than 10^{10}\GeV,
in a wide range of the gravitino mass m_{3/2}\simeq 10\MeV--100\TeV. If the
gravitino mass is in the range m_{3/2}\simeq 10\MeV--1\GeV as in the some
gauge-mediated supersymmetry breaking models, the dark matter in our universe
can be dominantly composed of the gravitino. Quantum fluctuation of the
during inflation causes an isocurvature fluctuation which may
be detectable in the future.Comment: 16 page
- âŠ