arXiv subjects

Seokcheon Lee

Publications and source records attributed to Seokcheon Lee.

At least 73 records · Page 4Linked to original sources

arXiv2014

Measuring the matter energy density and Hubble parameter from Large Scale Structure

We investigate the method to measure both the present value of the matter energy density contrast and the Hubble parameter directly from the measurement of the linear growth rate which is obtained from the large scale structure of the Universe. From this method, one can obtain the value of the nuisance cosmological parameter $\Omo$ (the present value of the matter energy density contrast) within 3% error if the growth rate measurement can be reached $z > 3.5$. One can also investigate the evolution of the Hubble parameter without any prior on the value of $H_0$ (the current value of the Hubble parameter). Especially, estimating the Hubble parameter are insensitive to the errors on the measurement of the normalized growth rate $f σ_8$. However, this method requires the high $z$ ($z > 3.5$) measurement of the growth rate in order to get the less than 5% errors on the measurements of $H(z)$ at $z \leq 1.2$ with the redshift bin $Δz = 0.2$. Thus, this will be suitable for the next generation large scale structure galaxy surveys like WFMOS and LSST.

astro-ph.CO↗

arXiv2014

Optimal strategies : theoretical approaches to the parametrization of the dark energy equation of state

The absence of compelling theoretical model requires the parameterizing the dark energy to probe its properties. The parametrization of the equation of state of the dark energy is a common method. We explore the theoretical optimization of the parametrization based on the Fisher information matrix. As a suitable parametrization, it should be stable at high redshift and should produce the determinant of the Fisher matrix as large as possible. For the illustration, we propose one parametrization which can satisfy both criteria. By using the proper parametrization, we can improve the constraints on the dark energy even for the same data. We also show the weakness of the so-called principal component analysis method.

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arXiv2014

Lagrangian perturbations theory : Third-order solution for general dark energy models

We investigate the Lagrangian perturbation theory of a general dark energy models with a constant equation of state, ω, and derive the fitting form of the fastest growing mode solutions up to the third order. These fitting forms are less than few % errors compared to the numerical calculation. We also correct the solutions of Einstein-de Sitter and the open universe with the proper initial conditions and the correct consideration for the growing mode solutions in order to compare with the general dark energy models. Even though these fitting forms are limited to the constant equation of state models, one can apply these to the time-varying ωby interpolating between models with the constant ω. These fitting forms can be used for the correct prediction for the two point correlation function and can give the proper predictions for the different dark energy models.

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arXiv2013

Cluster number counts in quintessence models

Even though the abundance and evolution of clusters have been used to study the cosmological parameters including the properties of dark energy owing to their pure dependence on the geometry of the Universe and the power spectrum, it is necessary to pay particular attention to the effects of dark energy on the analysis. We obtain the explicit dark energy dependent {\it rms} linear mass fluctuation $σ_8$ which is consistent with the CMB normalization with less than $2$ % errors for general constant dark energy equation of state, $\oQ$. Thus, we do not have any degeneracy between $σ_8$ and the matter energy density contrast $\Omo$. When we use the correct value of the critical density threshold $δ_{c} = 1.58$ obtained recently \cite{09090826, 09100126} into the cluster number density $n$ calculation in the Press-Schechter (PS) formalism, $n$ increases as compared to the one obtained by using $δ_{c} = 1.69$ by about $60$, $80$, and $110$ % at $z = 0$, $0.5$, and $1$, respectively. Thus, PS formalism predicts the cluster number consistent with both simulation and observed data at the high mass region. We also introduce the improved coefficients of Sheth-Tormen (ST) formalism, which is consistent with the recently suggested mass function \cite{10052239}. We found that changing $\oQ$ by $Δ\oQ = -0.1$ from $\oQ = -1.0$ causes the changing of the comoving numbers of high mass clusters of $M = 10^{16} h^{-1} M_{\odot}$ by about $20$ and $40$ % at $z = 0$ and $1$, respectively.

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arXiv2013

Constraints on the dark energy using multiple observations : snare of principal component analysis

We explore snares in determining the equation of state of dark energy ($ω$) when one uses the so-called principal component analysis for multiple observations. We demonstrated drawbacks of principal component analysis in an earlier paper. We used the Hubble parameter data generated from a fiducial model using the so-called Chevallier-Polarski-Linder parameterization. We extend our previous consideration to multiple observations, the Hubble parameter and the luminosity distance. We find that the principal component analysis produces the almost constant $ω$ even when a fiducial model is a rapidly varying $ω$. Thus, resolution of dynamical property of $ω$ through PCA is degraded especially when one fits to several observations.

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arXiv2012

Evidence for departure from ΛCDM with LSS

We investigate the growth index parameter γand the time variation of the gravitational constant G_{eff} by using the currently available growth function f(z) data at different redshifts, with and without scaling to the fiducial ΛCDM model. We inquire the four different models of γincluding a constant γ. From a χ^2 minimization, we constrain the parameter spaces of models and show that ΛCDM model is excluded by 1-σlevel from current f(z) data. G_{eff} is different from the Newton's gravitational constant G_{N} in modified gravity theories and interestingly, the current data shows that G_{eff} \neq G_{N} at z \gtrsim 0.2 \sim 0.3 at 3-σlevel. From these, we conclude that Einstein's General Relativity with ΛCDM is ruled out by 99% confidence level from large scale structure observations.

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arXiv2011

Drawbacks of Principal component analysis

One of the main tasks for present and future dark energy surveys is to determine whether the dark energy is dynamical or not. To illustrate this from data, it is commonly used to parameterize the dark energy equation of state w as several piecewise constant wis using the principal component analysis (PCA) method over finite redshift bins. We show that there is only $j-1$ free parameters wis if we choose the redshift as j bins. Without this constrain, one obtains the inconsistent results from the data analysis. Furthermore, if w decreases with non-negligible ratio as z does, then PCA fails to reproduce the original behavior of w. Also, time varying w can be confused with the incorrect value of constant one when the decreasing (or increasing) ratio of w is small but not negligible.

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arXiv2010

Constraints on scalar-tensor theories of gravity from observations

In spite of their original discrepancy, both dark energy and modified theory of gravity can be parameterized by the effective equation of state (EOS) $ω$ for the expansion history of the Universe. A useful model independent approach to the EOS of them can be given by so-called Chevallier-Polarski-Linder (CPL) parametrization where two parameters of it ($ω_{0}$ and $ω_{a}$) can be constrained by the geometrical observations which suffer from degeneracies between models. The linear growth of large scale structure is usually used to remove these degeneracies. This growth can be described by the growth index parameter $γ$ and it can be parameterized by $γ_{0} + γ_{a} (1 - a)$ in general. We use the scalar-tensor theories of gravity (STG) and show that the discernment between models is possible only when $γ_a$ is not negligible. We show that the linear density perturbation of the matter component as a function of redshift severely constrains the viable subclasses of STG in terms of $ω$ and $γ$. From this method, we can rule out or prove the viable STG in future observations. When we use $Z(ϕ) =1$, $F$ shows the convex shape of evolution in a viable STG model. The viable STG models with $Z(ϕ) = 1$ are not distinguishable from dark energy models when we strongly limit the solar system constraint.

astro-ph.CO↗

arXiv2010

Properties of the exact analytic solution of the growth factor and its applications

There have been the approximate analytic solution \cite{Silveria} and several approximate analytic forms \cite{0508156,Carroll,0303112} of the growth factor $D_{g}$ for the general dark energy models with the constant values of its equation of state $\omde$ after Heath found the exact integral form of the solution of $D_{g}$ for the Universe including the cosmological constant or the curvature term. Recently, we obtained the exact analytic solutions of the growth factor for both $\omde = -1$ or $-\fr{1}{3}$ \cite{SK1} and the general dark energy models with the constant equation of state $\omde$ \cite{SK3} independently. We compare the exact analytic solution of $D_{g}$ with the other well known approximate solutions. We also prove that the analytic solutions for $\omde = -1$ or $-\fr{1}{3}$ in Ref. \cite{SK1} are the specific solutions of the exact solutions of the growth factor for general $\omde$ models in Ref. \cite{SK3} even though they look quite different. We scrutinize the issue of using the well known parameterizations of the growth index and its parameter given in Ref. \cite{WS} to obtain the growth factor for general dark energy models. We also investigate the possible extensions of the exact solution of $D_{g}$ to the time-varying $\omde$ for the comparison with observations.

astro-ph.CO↗

arXiv2010

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 $δ$ 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 $ω_{de}$ 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, $0.25 \leq z \leq 1.5$, 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.

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arXiv2010

Effects on the two-point correlation function from the coupling of quintessence to dark matter

We investigate the effects of the nonminimal coupling between the scalar field dark energy (quintessence) and the dark matter on the two- point correlation function. It is well known that this coupling shifts the turnover scale as well as suppresses the amplitude of the matter power spectrum. However, these effects are too small to be observed when we limit the coupling strength to be consistent with observations. Since the coupling of quintessence to baryons is strongly constrained, species dependent coupling may arise. This results in a baryon bias that is dif- ferent from unity. Thus, we look over the correlation function in this coupled model. We find that even the non-coupled quintessence model gives the better fit to the correlation function compared to the cosmo- logical constant model. We are also able to observe the enhancement of the baryon acoustic oscillation (BAO) peak due to the increasing bias factor of baryon from this species dependent coupling. In order to avoid the damping effect of the BAO signature in the matter power spectrum due to nonlinear clustering, we consider the coupling effect on the BAO bump in the linear regime. This provides an alternative method to constrain the coupling of dark energy to dark matter.

astro-ph.CO↗

arXiv2009

Spherical collapse model with non-clustering dark energy

We investigate a spherical overdensity model for the non-clustering dark energy (DE) with the constant equation of state, w in a flat universe. In this case, the exact solution for the evolution of the scale factor is obtained for general w. We also obtain the exact (when w = - 1/3) and the approximate (when w neq -1/3) solutions for the ratio of the overdensity radius to its value at the turnaround epoch (y) for general cosmological parameters. Also the exact and approximate solutions of the overdensity at the turnaround epoch (zeta) are obtained for general w. Thus, we are able to obtain the non-linear overdensity Delta = 1 + delta at any epoch for the given DE model. The non-linear overdensity at the virial epoch (Delta_{vir}) is obtained by using the virial theorem and the energy conservation. The non-linear overdensity of every DE model converges to that of the Einstein de Sitter universe ~ 147 when z_{vir}increases. We find that the observed quantities at high redshifts are insensitive to the different w models. The low-redshift cluster (z_{vir} ~ 0.04, i.e., z_{ta} ~ 0.7) shows the most model dependent feature and it should be a suitable object for testing DE models. Also as Omo increases, the model dependence of the observed quantities decreases. The error in the approximate solutions is at most 2% for a wide range of the parameter space. Even though the analytic forms of y and ζare obtained for the constant w, they can be generalized to the slowly varying w. Thus, these analytic forms of the scale factor, y, and zeta provide a very accurate and useful tool for measuring the properties of DE.

astro-ph.CO↗

arXiv2009

Spherical collapse model with and without curvature

We investigate a spherical collapse model with and without the spatial curvature. We obtain the exact solutions of dynamical quantities such as the ratio of the scale factor to its value at the turnaround epoch and the ratio of the overdensity radius to its value at the turnaround time with general cosmological parameters. The exact solutions of the overdensity at the turnaround epoch for the different models are also obtained. Thus, we are able to obtain the nonlinear overdensity at any epoch for the given model. We obtain that the nonlinear overdensity of the Einstein de Sitter Universe is 18 pi^2(fr{1}{2pi} + fr{3}{4})^2 ~ 147 instead of the well known value 18 pi^2 ~ 178. In the open Universe, perturbations are virialized earlier than in flat Universe and thus clusters are denser at the virial epoch. Also the critical density threshold from the linear theory at the virialized epoch is obtained as fr{3}{20} (9pi+6)^{fr{2}{3}} ~ 1.58 instead of fr{3}{20} (12pi)^{fr{2}{3}} ~ 1.69. This value is same for the close and the open Universes. Because we obtain the analytic forms of dynamical quantities, we are able to estimate the abundances of both virialized and non-virialized clusters at any epoch. Also the temperature and luminosity functions are able to be computed at any epoch. Unfortunately, the current concordance model prefers the almost flat Universe and the above results might be restricted by the academic interests only. However, mathematical structure of the physical evolution equations of the curved space is identical with that of the dark energy with the equation of state w = -fr{1}{3}. Thus, we are able to extend these analytic solutions to the general dark energy model and they will provide the useful tools for probing the properties of dark energy.

astro-ph.CO↗

arXiv2009

Exact analytic solution of sub-horizon scales linear perturbation for general dark energy models

Three decades ago Heath found the integral form of the exact analytic growing mode solution of linear density perturbation $δ$ in sub-horizon scales including the cosmological constant or the curvature term. Interestingly, we are able to obtain the analytic solution for general dark energy models with the constant equation of state $ω_{de}$. We compare the correct analytic growing mode solution $δ$ with the text book solution $δ^{D}$. Indeed, both solutions are equal to each other when $ω_{de} = -1$. We also able to extend this solution for the specific form of time varying $ω_{de}$.

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arXiv2009

Growth index with the cosmological constant

We obtain the exact analytic form of the growth index at present epoch ($a=1$) in a flat universe with the cosmological constant ({\it i.e.} the dark energy with its equation of state $ω_{de} = -1$). For the cosmological constant, we obtain the exact value of the current growth index parameter $γ= 0.5547$, which is very close to the well known value 6/11. We also obtain the exact analytic solution of the growth factor for $ω_{de}$ = -1/3 or -1. We investigate the growth index and its parameter at any epoch with this exact solution. In addition to this, we are able to find the exact $Ω_{m}^{0}$ dependence of those observable quantities. The growth index is quite sensitive to $Ω_{m}^{0}$ at $z = 0.15$, where we are able to use 2dF observation. If we adopt 2dF value of growth index, then we obtain the constrain $0.11 \leq Ω_{m}^{0} \leq 0.37$ for the cosmological constant model. Especially, the growth index is quite sensitive to $Ω_{m}^{0}$ around $z \leq 1$. We might be able to obtain interesting observations around this epoch. Thus, the analytic solution for this growth factor provides the very useful tools for future observations to constrain the exact values of observational quantities at any epoch related to growth factor for $ω_{de} = -1$ or -1/3.

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arXiv2009

Dark matter growth and baryon bias in an accelerating universe

We investigate the exact analytic solutions for the growths of the dark matter and the baryon in sub-horizon scale. The growth of the dark matter $δ_{\DM}$ is related to that of the halos. Thus, the exact solution for the growth of the dark matter is important to obtain the proper properties of dark matter halos. However, the dark energy model dependence of $δ_{\DM}$ is confused with the $δ_{\DM}$ dependence on $Ω_{m}^{0}$. Thus, the careful investigation is necessary for the $δ_{\DM}$ dependence on dark energy models. We also obtain the exact solution of the growth of the baryon $δ_{\B}$ which can be used to obtain the baryon bias factor $b(a)$. This might be able to be observed in intracluster gas or in Lyman-$α$ clouds. However, $b(a)$ is quite model independent. Recently, we obtained the exact analytic solution for the growing mode solution of the matter linear density perturbation $δ$ on sub-horizon scale for general dark energy model \cite{SK}. This solution is not same as the well known approximate analytic solution \cite{Waga}. The exact analytic solution shows the same evolution behavior of the growth factor obtained numerically. However, the exact solution is simple and useful for the extension to other models including modified gravity theories. Furthermore, it guides to the fact that the growth index parameter depends on both models $ω_{\de}$ and $Ω_{m}^{0}$ and thus we need to be careful for applying the fitting formulae to the general models \cite{WS}. The exact analytic solutions for the growth factor will provide the more accurate tools for the weak lensing, the number density of clusters, their mass and etc.

astro-ph.CO↗

arXiv2008

Lee Wick Dark Energy

We consider the cosmological application of Lee-Wick theory where a field has a higher derivative kinetic operators. The higher derivative term can be eliminated by introducing a set of auxiliary fields. We investigate the cosmological evolutions of these fields as a candidate of dark energy. This model has the same structure as so called ``quintom' model except the form of potentials and the sign of the slope of the potentials. This model can give the stable late time phantom dominated scaling solution ($ω_{\DE} < -1$) or tracking attractors ($ω_{\DE} = 0$) depending on the choice of the slopes of the potential. In order to be a viable dark energy candidate, the present energy density contrast of dark energy ($Ω_{\DE}^{(0)}$) should be close to an observed value (0.73) at the same time. However, a simple toy model of the theory can not satisfy both $ω_{\DE}^{(0)} \simeq -1$ and $Ω_{\DE}^{(0)} = 0.73$. If we include the self interaction term of Lee Wick field, then we are able to produce the observed values of those quantities. However, in this case we are not be able to have the stable solutions and we need to suffer from the fine tuning of its mass.

astro-ph↗

arXiv2008

Anisotropy due to Brans-Dicke Theory

It is well known that the viscous Bianchi type-I metric of the Kasner form is not able to describe an anisotropic universe, which satisfies the second law of thermodynamics and the dominant energy condition in Einstein's theory of gravity. We investigate this problem in Brans-Dicke theory of gravity using the Bianchi type-I metric with the perfect fluid. We show that it is possible to have the dominant energy condition and the growth of entropy in this model. Also we apply this model to explain the anomaly concerning the low quadrupole amplitude of the angular power spectrum of the temperature anisotropy observed in WMAP data.

gr-qc↗