301 research outputs found
Graviton Mode Function in Inflationary Cosmology
We consider the production of gravitons in an inflationary cosmology by
approximating each epoch of change in the equation of state as sudden, from
which a simple analytic graviton mode function has been derived. We use this
mode function to compute the graviton spectral energy density and the
tensor-induced cosmic microwave background anisotropy. The results are then
compared to the numerical calculations which incorporate a smooth
radiation-matter phase transition. We find that the sudden approximation is a
fairly good method. Besides, in determining the frequency range and amplitude
of the mode function, we introduce a pre-inflationary radiation-dominated epoch
and use a physically sensible regularization method.Comment: 26 pages, revtex, 4 figures (available upon request). We have added a
new Section VIII with four new figures, in which Eq. (35) is used to
calculate the graviton spectral energy density and the tensor-induced CMB
anisotrop
Growth index with the exact analytic solution of sub-horizon scale linear perturbation for dark energy models with constant equation of state
Three decades ago Heath found the integral form of the exact analytic growing
mode solution of the linear density perturbation on sub-horizon scales
including the cosmological constant or the curvature term. Recently, we
obtained the exact analytic form of this solution in our previous work
\cite{SK}. Interestingly, we are able to extend this solution for general dark
energy models with the constant equation of state in a flat
universe. This analytic solution provides the accurate and efficient tools for
probing the properties of dark energy models such as the behavior of the growth
factor and the growth index. We investigate the growth index and its parameter
at any epoch with this exact solution for different dark energy models and find
that the growth index is quite model dependent in the redshift space, , so observations of the structure growth around this epoch
would be very interesting. Also one may be able to rule out some dark energy
models by using the analysis from this exact solution. Thus, the analytic
solution for the growth factor provides the very useful tools for future
observations to constrain the exact values of observational quantities at any
epoch related to the growth factor in the dark energy models.Comment: 8pages, 3figures, 1Table, minor revisions to match version accepted
by PLB (add Fig1
Primordial Black Holes from Passive Density Fluctuations
In this paper, we show that if passive fluctuations are considered,
primordial black holes (PBHs) can be easily produced in the framework of
single-field, slow-roll inflation models. The formation of PBHs is due to the
blue spectrum of passive fluctuations and an enhancement of the spectral range
which exits horizon near the end of inflation. Therefore the PBHs are light
with masses depending on the number of e-folds when the
scale of our observable universe leaves horizon. These PBHs are likely to have
evaporated and cannot be a candidate for dark matter but they may still affect
the early universe.Comment: 7 pages, 1 figure, to appear in Physics Letters
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