55 research outputs found

### Small-scale Effects of Thermal Inflation on Halo Abundance at High-$z$, Galaxy Substructure Abundance and 21-cm Power Spectrum

We study the impact of thermal inflation on the formation of cosmological
structures and present astrophysical observables which can be used to constrain
and possibly probe the thermal inflation scenario. These are dark matter halo
abundance at high redshifts, satellite galaxy abundance in the Milky Way, and
fluctuation in the 21-cm radiation background before the epoch of reionization.
The thermal inflation scenario leaves a characteristic signature on the matter
power spectrum by boosting the amplitude at a specific wavenumber determined by
the number of e-foldings during thermal inflation ($N_{\rm bc}$), and strongly
suppressing the amplitude for modes at smaller scales. For a reasonable range
of parameter space, one of the consequences is the suppression of minihalo
formation at high redshifts and that of satellite galaxies in the Milky Way.
While this effect is substantial, it is degenerate with other cosmological or
astrophysical effects. The power spectrum of the 21-cm background probes this
impact more directly, and its observation may be the best way to constrain the
thermal inflation scenario due to the characteristic signature in the power
spectrum. The Square Kilometre Array (SKA) in phase 1 (SKA1) has sensitivity
large enough to achieve this goal for models with $N_{\rm bc}\gtrsim 26$ if a
10000-hr observation is performed. The final phase SKA, with anticipated
sensitivity about an order of magnitude higher, seems more promising and will
cover a wider parameter space.Comment: 28 pages, 8 figure

### The Possibility of Inflation in Asymptotically Safe Gravity

We examine the inflationary modes in the cubic curvature theories in the
context of asymptotically safe gravity. On the phase space of the Hubble
parameter, there exists a critical point which corresponds to the slow-roll
inflation in Einstein frame. Most of the e-foldings are attained around the
critical point for each inflationary trajectories. If the coupling constants
$g_i$ have the parametric relations generated as the power of the relative
energy scale of inflation $H_0$ to the ultraviolet cutoff $\Lambda$, a
successful inflation with more than 60 e-foldings occurs near the critical
point.Comment: 14 pages, 4 figure

### Critical Reviews of Causal Patch Measure over the Multiverse

In this talk, the causal patch measure based on black hole complementarity is
critically reviewed. By noticing the similarities between the causal structure
of an inflationary dS space and that of a black hole, we have considered the
complementarity principle between the inside and the outside of the causal
horizon as an attractive way to count the inflationary multiverse. Even though
the causal patch measure relieves the Boltzmann brain problem and stresses
physical reality based on observations, it could be challenged by the
construction of counterexamples, both on regular black holes and charged black
holes, to black hole complementarity.Comment: 6 pages, 2 figures; A proceeding for CosPA2008. Talk on the 29th of
October, 2008, Pohang, Kore

### CMB Spectral Distortion Constraints on Thermal Inflation

Thermal inflation is a second epoch of exponential expansion at typical
energy scales $V^{1/4} \sim 10^{6 \sim 8} \mathrm{GeV}$. If the usual
primordial inflation is followed by thermal inflation, the primordial power
spectrum is only modestly redshifted on large scales, but strongly suppressed
on scales smaller than the horizon size at the beginning of thermal inflation,
$k > k_{\rm b} = a_{\rm b} H_{\rm b}$. We calculate the spectral distortion of
the cosmic microwave background generated by the dissipation of acoustic waves
in this context. For $k_{\rm b} \ll 10^3 \mathrm{Mpc}^{-1}$, thermal inflation
results in a large suppression of the $\mu$-distortion amplitude, predicting
that it falls well below the standard value of $\mu \simeq 2\times 10^{-8}$.
Thus, future spectral distortion experiments, similar to PIXIE, can place new
limits on the thermal inflation scenario, constraining $k_{\rm b} \gtrsim 10^3
\mathrm{Mpc}^{-1}$ if $\mu \simeq 2\times 10^{-8}$ were found.Comment: 18 pages, 7 figure

### Minkowski Tensors in Two Dimensions - Probing the Morphology and Isotropy of the Matter and Galaxy Density Fields

We apply the Minkowski Tensor statistics to two dimensional slices of the
three dimensional density field. The Minkowski Tensors are a set of functions
that are sensitive to directionally dependent signals in the data, and
furthermore can be used to quantify the mean shape of density peaks. We begin
by introducing our algorithm for constructing bounding perimeters around
subsets of a two dimensional field, and reviewing the definition of Minkowski
Tensors. Focusing on the translational invariant statistic $W^{1,1}_{2}$ - a $2
\times 2$ matrix - we calculate its eigenvalues for both the entire excursion
set ($\Lambda_{1},\Lambda_{2}$) and for individual connected regions and holes
within the set ($\lambda_{1},\lambda_{2}$). The ratio of eigenvalues
$\Lambda_{2}/\Lambda_{1}$ informs us of the presence of global anisotropies in
the data, and $\langle \lambda_{2}/\lambda_{1} \rangle$ is a measure of the
mean shape of peaks and troughs in the density field. We study these quantities
for a Gaussian field, then consider how they are modified by the effect of
gravitational collapse using the latest Horizon Run 4 cosmological simulation.
We find $\Lambda_{1,2}$ are essentially independent of gravitational collapse,
as the process maintains statistical isotropy. However, the mean shape of peaks
is modified significantly - overdensities become relatively more circular
compared to underdensities of the same area. When applying the statistic to a
redshift space distorted density field, we find a significant signal in the
eigenvalues $\Lambda_{1,2}$, suggesting that they can be used to probe the
large-scale velocity field.Comment: 17 pages, accepted for publication in AP

### Anthropic Likelihood for the Cosmological Constant and the Primordial Density Perturbation Amplitude

Weinberg et al. calculated the anthropic likelihood of the cosmological
constant using a model assuming that the number of observers is proportional to
the total mass of gravitationally collapsed objects, with mass greater than a
certain threshold, at t \rightarrow \infty. We argue that Weinberg's model is
biased toward small \Lambda, and to try to avoid this bias we modify his model
in a way that the number of observers is proportional to the number of
collapsed objects, with mass and time equal to certain preferred mass and time
scales. Compared to Weinberg's model, this model gives a lower anthropic
likelihood of \Lambda_0 (T_+(\Lambda_0) ~ 5%). On the other hand, the anthropic
likelihood of the primordial density perturbation amplitude from this model is
high, while the likelihood from Weinberg's model is low. Furthermore, observers
will be affected by the history of the collapsed object, and we introduce a
method to calculate the anthropic likelihoods of \Lambda and Q from the mass
history using the extended Press-Schechter formalism. The anthropic likelihoods
for $\Lambda$ and Q from this method are similar to those from our single mass
constraint model, but, unlike models using the single mass constraint which
always have degeneracies between \Lambda and Q, the results from models using
the mass history are robust even if we allow both \Lambda and Q to vary. In the
case of Weinberg's flat prior distribution of \Lambda (pocket based multiverse
measure), our mass history model gives T_+(\Lambda_0) ~ 10%, while the scale
factor cutoff measure and the causal patch measure give T_+(\Lambda_0) \geq
30%.Comment: 28 pages, 10 figure

### Modeling Cosmological Perturbations of Thermal Inflation

We consider a simple system consisting of matter, radiation and vacuum
components to model the impact of thermal inflation on the evolution of
primordial perturbations. The vacuum energy magnifies the modes entering the
horizon before its domination, making them potentially observable, and the
resulting transfer function reflects the phase changes and energy contents. To
determine the transfer function, we follow the curvature perturbation from well
outside the horizon during radiation domination to well outside the horizon
during vacuum domination and evaluate it on a constant radiation density
hypersurface, as is appropriate for the case of thermal inflation. The shape of
the transfer function is determined by the ratio of vacuum energy to radiation
at matter-radiation equality, which we denote by $\upsilon$, and has two
characteristic scales, $k_{\rm a}$ and $k_{\rm b}$, corresponding to the
horizon sizes at matter radiation equality and the beginning of the inflation,
respectively. If $\upsilon \ll 1$, the universe experiences radiation, matter
and vacuum domination eras and the transfer function is flat for $k \ll k_{\rm
b}$, oscillates with amplitude $1/5$ for $k_{\rm b} \ll k \ll k_{\rm a}$ and
oscillates with amplitude $1$ for $k \gg k_{\rm a}$. For $\upsilon \gg 1$, the
matter domination era disappears, and the transfer function reduces to being
flat for $k \ll k_{\rm b}$ and oscillating with amplitude $1$ for $k \gg k_{\rm
b}$.Comment: 17 pages, 5 figures, submitted to JCA

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