479 research outputs found
Relaxing Constraints on Inflation Models with Curvaton
We consider the effects of the curvaton, late-decaying scalar condensation,
to observational constraints on inflation models. From current observations of
cosmic density fluctuations, severe constraints on some class of inflation
models are obtained, in particular, on the chaotic inflation with higher-power
monomials, the natural inflation, and the new inflation. We study how the
curvaton scenario changes (and relaxes) the constraints on these models.Comment: 18 pages, 6 figure
METODE ROLE PLAY UNTUK MENINGKATKAN MOTIVASI SISWA KELAS 6 SD UNTUK BERBICARA DALAM BAHASA INGGRIS
Untuk menghilangkan suasana kebosanan, ketakntan, dan kesulitan di dalam bela jar speaking, maka perlu \ll1tuk menggllllakan metode-metode tertentu yang dapat menciptakan suasana barn yang menarik dan memudahkan siswa di dalam belajar. Siswa SDN Mojo V yang sering menggooakan cara tradisional di dalam pembelajaran bahasa Inggris perlu \ll1mk mendapatkan masukan \ll1tuk peningkatan kemampuan mereka khususnya dalam berbicara bahasa Inggris. Memang ada banyak sekali metode-metode yang dapat digllllakan \ll1tuk mengajarkan speaking, tetapi penulis menggllllakan role play sebagai metode pengajaran speaking untuk mereka. Sebagai salah satu metode dari berbagai metode yang ada, role play memang memp\ll1yai kelebihan dan kekurangan khususnya ill dalam penerapannya di tingkat kelas 6 SD.
Berbeda dengan tingkat SLTP, SLT A, alau Perguruan Tinggi, tingkat kelas 6 SD membutuhkan waktu relatif lebih lama dalam pelaksanaannya. Selain itu pengajar juga masih perIu memikirkan dialog yang akan diucapkan pada situasi-situasi yang ada pada permainan peran ini. Pada tingkatan ini, juga sulit bagi pengajar \ll1tuk mengajarkan berbicara bahasa Inggris dan struktur secara bersamaan, sekalipun keduanya tidak dapat dipisahkan, Dalam hal ini penuli
Effect of Background Evolution on the Curvaton Non-Gaussianity
We investigate how the background evolution affects the curvature
perturbations generated by the curvaton, assuming a curvaton potential that may
deviate slightly from the quadratic one, and parameterizing the background
fluid density as \rho\propto a^{-\alpha}, where a is the scale factor, and
\alpha depends on the background fluid. It turns out that the more there is
deviation from the quadratic case, the more pronounced is the dependence of the
curvature perturbation on \alpha. We also show that the background can have a
significant effect on the nonlinearity parameters f_NL and g_NL. As an example,
if at the onset of the curvaton oscillation there is a dimension 6 contribution
to the potential at 5 % level and the energy fraction of the curvaton to the
total one at the time of its decay is at 1 %, we find variations \Delta f_NL
\sim \mathcal{O}(10) and \Delta g_NL \sim \mathcal{O}(10^4) between matter and
radiation dominated backgrounds. Moreover, we demonstrate that there is a
relation between f_NL and g_NL that can be used to probe the form of the
curvaton potential and the equation of state of the background fluid.Comment: 14 pages, 8 figure
Density Fluctuations in Thermal Inflation and Non-Gaussianity
We consider primordial fluctuations in thermal inflation scenario. Since the
thermal inflation drives about 10 -folds after the standard inflation, the
time of horizon-exit during inflation corresponding to the present
observational scale shifts toward the end of inflation. It generally makes the
primordial power spectrum more deviated from a scale-invariant one and hence
renders some models inconsistent with observations. We present a mechanism of
generating the primordial curvature perturbation at the end of thermal
inflation utilizing a fluctuating coupling of a flaton field with the fields in
thermal bath. We show that, by adopting the mechanism, some inflation models
can be liberated even in the presence of the thermal inflation. We also discuss
non-Gaussianity in the mechanism and show that large non-Gaussianity can be
generated in this scenario.Comment: 15 pages, 1 figures, minor change
The Subdominant Curvaton
We present a systematic study of the amplitude of the primordial perturbation
in curvaton models with self-interactions, treating both renormalizable and
non-renormalizable interactions. In particular, we consider the possibility
that the curvaton energy density is subdominant at the time of the curvaton
decay. We find that large regions in the parameter space give rise to the
observed amplitude of primordial perturbation even for non-renormalizable
curvaton potentials, for which the curvaton energy density dilutes fast. At the
time of its decay, the curvaton energy density may typically be subdominant by
a relative factor of 10^-3 and still produce the observed perturbation. Field
dynamics turns out to be highly non-trivial, and for non-renormalizable
potentials and certain regions of the parameter space we observe a
non-monotonous relation between the final curvature perturbation and the
initial curvaton value. In those cases, the time evolution of the primordial
perturbation also displays an oscillatory behaviour before the curvaton decay.Comment: Acknowledgments of financial support added, no further change
Scale-dependence of Non-Gaussianity in the Curvaton Model
We investigate the scale-dependence of f_NL in the self-interacting curvaton
model. We show that the scale-dependence, encoded in the spectral index
n_{f_NL}, can be observable by future cosmic microwave background observations,
such as CMBpol, in a significant part of the parameter space of the model. We
point out that together with information about the trispectrum g_NL, the
self-interacting curvaton model parameters could be completely fixed by
observations. We also discuss the scale-dependence of g_NL and its implications
for the curvaton model, arguing that it could provide a complementary probe in
cases where the theoretical value of n_{f_NL} is below observational
sensitivity.Comment: 14 pages, 5 figures, Eq.(10) correcte
The Hubble constant and dark energy from cosmological distance measures
We study how the determination of the Hubble constant from cosmological
distance measures is affected by models of dark energy and vice versa. For this
purpose, constraints on the Hubble constant and dark energy are investigated
using the cosmological observations of cosmic microwave background, baryon
acoustic oscillations and type Ia suprenovae. When one investigates dark
energy, the Hubble constant is often a nuisance parameter, thus it is usually
marginalized over. On the other hand, when one focuses on the Hubble constant,
simple dark energy models such as a cosmological constant and a constant
equation of state are usually assumed. Since we do not know the nature of dark
energy yet, it is interesting to investigate the Hubble constant assuming some
types of dark energy and see to what extent the constraint on the Hubble
constant is affected by the assumption concerning dark energy. We show that the
constraint on the Hubble constant is not affected much by the assumption for
dark energy. We furthermore show that this holds true even if we remove the
assumption that the universe is flat. We also discuss how the prior on the
Hubble constant affects the constraints on dark energy and/or the curvature of
the universe.Comment: 45 pages, 15 figure
Cosmic Density Perturbations from Late-Decaying Scalar Condensations
We study the cosmic density perturbations induced from fluctuation of the
amplitude of late-decaying scalar condensations (called \phi) in the scenario
where the scalar field \phi once dominates the universe. In such a scenario,
the cosmic microwave background (CMB) radiation originates to decay products of
the scalar condensation and hence its anisotropy is affected by the fluctuation
of \phi. It is shown that the present cosmic density perturbations can be
dominantly induced from the primordial fluctuation of \phi, not from the
fluctuation of the inflaton field. This scenario may change constraints on the
source of the density perturbations, like inflation. In addition, a correlated
mixture of adiabatic and isocurvature perturbations may arise in such a
scenario; possible signals in the CMB power spectrum are discussed. We also
show that the simplest scenario of generating the cosmic density perturbations
only from the primordial fluctuation of \phi (i.e., so-called ``curvaton''
scenario) is severely constrained by the current measurements of the CMB
angular power spectrum if correlated mixture of the adiabatic and isocurvature
perturbations are generated.Comment: 31pages, 14figure
- …