3,847 research outputs found
Cosmological CMBR dipole in open universes ?
The observed CMBR dipole is generally interpreted as a Doppler effect arising
from the motion of the Earth relative to the CMBR frame. An alternative
interpretation, proposed in the last years, is that the dipole results from
ultra-large scale isocurvature perturbations. We examine this idea in the
context of open cosmologies and show that the isocurvature interpretation is
not valid in an open universe, unless it is extremely close to a flat universe,
.Comment: 26 pages, Latex, 6 figures, to appear in Phys. Rev.
Scalar potential from de Sitter brane in 5D and effective cosmological constant
We derive the scalar potential in zero mode effective action arising from a
de Sitter brane embedded in five dimensions with bulk cosmological constant
. The scalar potential for a scalar field canonically normalized is
given by the sum of exponential potentials. In the case of and
, we point out that the scalar potential has an unstable local
maximum at the origin and exponentially vanishes for large positive scalar
field. In the case of , the scalar potential has an unstable local
maximum at the origin and a stable local minimum, it is shown that the positive
cosmological constant in brane is reduced by negative potential energy of
scalar at minimum.Comment: 14 pages, 5 figures, add the section of cosmological implication
Scalar Kaluza-Klein modes in a multiply warped braneworld
The Kaluza-Klein (KK) modes of a massive scalar field on a 3-brane embedded
in six dimensional multiply warped spacetime are determined. Due to the
presence of warping along both the extra dimensions the KK mass spectrum splits
into two closely spaced branches which is a distinct feature of this model
compared to the five dimensional Randall-Sundrum model. This new cluster of the
KK mode spectrum is expected to have interesting phenomenological implications
for the upcoming collider experiments. Such a scenario may also be extended for
even larger number of orbifolded extra dimensions.Comment: 10 pages, Revte
Correlated adiabatic and isocurvature perturbations from double inflation
It is shown that double inflation (two minimally coupled massive scalar
fields) can produce correlated adiabatic and isocurvature primordial
perturbations. Depending on the two relevant parameters of the model, the
contributions to the primordial perturbations are computed, with special
emphasis on the correlation, which can be quantitatively represented by a
correlation spectrum. Finally the primordial spectra are evolved numerically to
obtain the CMBR anisotropy multipole expectation values. It turns out that the
existence of mixing and correlation can alter very significantly the
temperature fluctuation predictions.Comment: 23 pages, 7 figures, RevTex. To appear in Phys. Rev.
Bulk gravitons from a cosmological brane
We investigate the emission of gravitons by a cosmological brane into an Anti
de Sitter five-dimensional bulk spacetime. We focus on the distribution of
gravitons in the bulk and the associated production of `dark radiation' in this
process. In order to evaluate precisely the amount of dark radiation in the
late low-energy regime, corresponding to standard cosmology, we study
numerically the emission, propagation and bouncing off the brane of bulk
gravitons.Comment: 27 pages, 5 figures, minor corrections. Final versio
Limits on the integration constant of the dark radiation term in Brane Cosmology
We consider the constraints from primordial Helium abundances on the constant
of integration of the dark radiation term of the brane-world generalized
Friedmann equation derived from the Randall-Sundrum Single brane model. We
found that -- using simple, approximate and semianalytical Method -- that the
constant of integration is limited to be between -8.9 and 2.2 which limits the
possible contribution from dark radiation term to be approximately between -27%
to 7% of the background photon energy density.Comment: 8 page
Cosmic Microwave Background Dipole induced by double inflation
The observed CMBR dipole is generally interpreted as the consequence of the
peculiar motion of the Sun with respect to the reference frame of the CMBR.
This article proposes an alternative interpretation in which the observed
dipole is the result of isocurvature perturbations on scales larger than the
present Hubble radius. These perturbations are produced in the simplest model
of double inflation, depending on three parameters. The observed dipole and
quadrupole can be explained in this model, while severely constraining its
parameters.Comment: Latex, 9 pages, no figure, to appear in Phys. Rev.
Non-linear isocurvature perturbations and non-Gaussianities
We study non-linear primordial adiabatic and isocurvature perturbations and
their non-Gaussianity. After giving a general formulation in the context of an
extended delta N-formalism, we analyse in detail two illustrative examples. The
first is a mixed curvaton-inflaton scenario in which fluctuations of both the
inflaton and a curvaton (a light isocurvature field during inflation)
contribute to the primordial density perturbation. The second example is that
of double inflation involving two decoupled massive scalar fields during
inflation. In the mixed curvaton-inflaton scenario we find that the bispectrum
of primordial isocurvature perturbations may be large and comparable to the
bispectrum of adiabatic curvature perturbations.Comment: 24 pages, typos corrected, references adde
From heaviness to lightness during inflation
We study the quantum fluctuations of scalar fields with a variable effective
mass during an inflationary phase. We consider the situation where the
effective mass depends on a background scalar field, which evolves during
inflation from being frozen into a damped oscillatory phase when the Hubble
parameter decreases below its mass. We find power spectra with suppressed
amplitude on large scales, similar to the standard massless spectrum on small
scales, and affected by modulations on intermediate scales. We stress the
analogies and differences with the parametric resonance in the preheating
scenario. We also discuss some potentially observable consequences when the
scalar field behaves like a curvaton.Comment: 23 pages; 8 figures; published versio
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