367 research outputs found
Conditions for Successful Extended Inflation
We investigate, in a model-independent way, the conditions required to obtain
a satisfactory model of extended inflation in which inflation is brought to an
end by a first-order phase transition. The constraints are that the correct
present strength of the gravitational coupling is obtained, that the present
theory of gravity is satisfactorily close to general relativity, that the
perturbation spectra from inflation are compatible with large scale structure
observations and that the bubble spectrum produced at the phase transition
doesn't conflict with the observed level of microwave background anisotropies.
We demonstrate that these constraints can be summarized in terms of the
behaviour in the conformally related Einstein frame, and can be compactly
illustrated graphically. We confirm the failure of existing models including
the original extended inflation model, and construct models, albeit rather
contrived ones, which satisfy all existing constraints.Comment: 8 pages RevTeX file with one figure incorporated (uses RevTeX and
epsf). Also available by e-mailing ARL, or by WWW at
http://star-www.maps.susx.ac.uk/papers/infcos_papers.html; Revised to include
extra references, results unchanged, to appear Phys Rev
Matching WMAP 3-yrs results with the Cosmological Slingshot Primordial Spectrum
We consider a recently proposed scenario for the generation of primordial
cosmological perturbations, the so called Cosmological Slingshot scenario. We
firstly obtain a general expression for the Slingshot primordial power spectrum
which extends previous results by including a blue pre-bounce residual
contribution at large scales. Starting from this expression we numerically
compute the CMB temperature and polarization power spectra arising from the
Slingshot scenario and show that they excellently match the standard WMAP
3-years best-fit results. In particular, if the residual blue spectrum is far
above the largest WMAP observed scale, the Slingshot primordial spectrum fits
the data well by only fixing its amplitude and spectral index at the pivot
scale k_p=10^{-3}h x Mpc^{-1}. We finally show that all possible distinctive
Slingshot signatures in the CMB power spectra are confined to very low
multipoles and thus very hard to detect due to large cosmic variance dominated
error bars at these scales.Comment: 9 pages, 4 figures; v3 clarifications added, version accepted for
publication in Gen. Rel. Grav. 200
Curvature perturbation spectrum from false vacuum inflation
In the inflationary cosmology it occurs frequently that the inflaton field is
trapped in a local, transient minimum with non-zero vacuum energy. The
difficulty regarding the curvature perturbation produced during such a stage is
that classically the inflaton does not move so that the comoving hypersurfaces
are not well defined at linear order in the scalar field perturbation. In this
paper, assuming a mechanism of trapping which resembles a high temperature
correction to the potential, we explicitly calculate for the first time the
resulting power spectrum of the curvature perturbation by evaluating the
quantum two-point correlation function directly. The spectrum is steeply blue
with the spectral index n_R = 4.Comment: (v1) 17 pages, no figure; (v2) 18 pages, more clarifications and
discussions added, to appear in JCA
On the inflationary flow equations
I explore properties of the inflationary flow equations. I show that the flow
equations do not correspond directly to inflationary dynamics. Nevertheless,
they can be used as a rather complicated algorithm for generating inflationary
models. I demonstrate that the flow equations can be solved analytically and
give a closed form solution for the potentials to which flow equation solutions
correspond. I end by considering some simpler algorithms for generating
stochastic sets of slow-roll inflationary models for confrontation with
observational data.Comment: 4 pages RevTeX4 file. Corrected typos in Eqs 11 and 13. Supersedes
journal versio
Constraints on inflation in closed universe
We investigate inflation in closed Friedmann-Robertson-Walker universe filled
with the scalar field with power-law potential. For a wide range of powers and
parameters of the potential we numerically calculated the slow-roll parameters
and scalar spectral index at the epoch when present Hubble scale leaves the
horizon and at the end of inflation. Also we compare results of our numerical
calculations with recent observation data. This allows us to set a constraint
on the power of the potential: alpha < (3.5 - 4.5).Comment: 5 pages, 5 figures; extended versio
Power Spectrum in Krein Space Quantization
The power spectrum of scalar field and space-time metric perturbations
produced in the process of inflation of universe, have been presented in this
paper by an alternative approach to field quantization namely, Krein space
quantization [1,2]. Auxiliary negative norm states, the modes of which do not
interact with the physical world, have been utilized in this method. Presence
of negative norm states play the role of an automatic renormalization device
for the theory.Comment: 8 pages, appear in Int. J. Theor. Phy
Observational constraints on braneworld chaotic inflation
We examine observational constraints on chaotic inflation models in the
Randall-Sundrum Type II braneworld. If inflation takes place in the high-energy
regime, the perturbations produced by the quadratic potential are further from
scale-invariance than in the standard cosmology, in the quartic case more or
less unchanged, while for potentials of greater exponent the trend is reversed.
We test these predictions against a data compilation including the WMAP
measurements of microwave anisotropies and the 2dF galaxy power spectrum. While
in the standard cosmology the quartic potential is at the border of what the
data allow and all higher powers excluded, we find that in the high-energy
regime of braneworld inflation even the quadratic case is under strong
observational pressure. We also investigate the intermediate regime where the
brane tension is comparable to the inflationary energy scale, where the
deviations from scale-invariance prove to be greater.Comment: 5 pages RevTeX4 file with three figures incorporated. Minor changes
to match version accepted by Physical Review
The Tensor to Scalar Ratio of Phantom Dark Energy Models
We investigate the anisotropies in the cosmic microwave background in a class
of models which possess a positive cosmic energy density but negative pressure,
with a constant equation of state w = p/rho < -1. We calculate the temperature
and polarization anisotropy spectra for both scalar and tensor perturbations by
modifying the publicly available code CMBfast. For a constant initial curvature
perturbation or tensor normalization, we have calculated the final anisotropy
spectra as a function of the dark energy density and equation of state w and of
the scalar and tensor spectral indices. This allows us to calculate the
dependence of the tensor-to-scalar ratio on w in a model with phantom dark
energy, which may be important for interpreting any future detection of
long-wavelength gravitational waves.Comment: 5 pages, 4 figure
Primordial black hole production due to preheating
During the preheating process at the end of inflation the amplification of
field fluctuations can lead to the amplification of curvature perturbations. If
the curvature perturbations on small scales are sufficiently large, primordial
black holes (PBHs) will be overproduced. In this paper we study PBH production
in the two-field preheating model with quadratic inflaton potential. We show
that for many values of the inflaton mass m, and coupling g, small scale
perturbations will be amplified sufficiently, before backreaction can shut off
preheating, so that PBHs will be overproduced during the subsequent radiation
dominated era.Comment: 5 pages, 3 eps figures. Minor changes to match version to appear in
PRD as a rapid communicatio
Inflation with blowing-up solution of cosmological constant problem
The cosmological constant problem is how one chooses, without fine-tuning,
one singular point for the 4D cosmological constant. We argue
that some recently discovered {\it weak self-tuning} solutions can be viewed as
blowing-up this one point into a band of some parameter. These weak self-tuning
solutions may have a virtue that only de Sitter space solutions are allowed
outside this band, allowing an inflationary period. We adopt the hybrid
inflation at the brane to exit from this inflationary phase and to enter into
the standard Big Bang cosmology.Comment: LaTeX file of 20 pages including 2 eps figure
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