Seokcheon Lee

Effect on cosmic microwave background polarization of coupling of quintessence to pseudoscalar formed from the electromagnetic field and its dual

We present the full set of power spectra of cosmic microwave background (CMB) temperature and polarization anisotropies due to the coupling between quintessence and pseudoscalar of electromagnetism. This coupling induces a rotation of the polarization plane of the CMB, thus resulting in a nonvanishing B mode and parity-violating TB and EB modes. Using the BOOMERANG data from the flight of 2003, we derive the most stringent constraint on the coupling strength. We find that in some cases the rotation-induced B mode can confuse the hunting for the gravitational lensing-induced B mode.

Constraints on the coupled quintessence from cosmic microwave background anisotropy and matter power spectrum

We discuss the evolution of linear perturbations in a quintessence model in which the scalar field is nonminimally coupled to cold dark matter. We consider the effects of this coupling on both cosmic microwave background temperature anisotropies and matter perturbations. Because of the modification of the scale of cold dark matter as {rho}{sub c}={rho}{sub c}{sup (0)}a{sup -3+{xi}}, we can shift the turnover in the matter power spectrum even without changing the present energy densities of matter and radiation. This can be used to constrain the strength of the coupling. We find that the phenomenology of this model is consistent with current observations up to the coupling power n{sub c}{<=}0.01 while adopting the current parameters measured by the Wilkinson Microwave Anisotropy Probe. Upcoming cosmic microwave background observations continuing to focus on resolving the higher peaks may put strong constraints on the strength of the coupling.

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, ωde in a flat universe. In this case, the exact solution for the evolution of the scale factor is obtained for general ωde. We also obtain the exact (when ωde = −1/3) and the approximate (when ωde≠−1/3) solutions for the ratio of the overdensity radius to its value at the turnaround epoch (y≡R/Rta) for general cosmological parameters. Also the exact and approximate solutions of the overdensity at the turnaround epoch ζ = (ρcluster/ρm)|z = zta are obtained for general ωde. Thus, we are able to obtain the non-linear overdensity Δ≡1+δNL = ζ(x/y)3 at any epoch for the given DE model. The non-linear overdensity at the virial epoch Δvir = ζ(xvir/yvir)3 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 ΔvirEdS = 18π2((1/2π)+(3/4))2 147 when zvir increases. We find that the observed quantities at high redshifts are insensitive to the different ωde models. The low-redshift cluster (zvir ~ 0.04, i.e., zta ~ 0.7) shows the most model dependent feature and it should be a suitable object for testing DE models. Also as ΩM0 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 ζ are obtained for the constant ωde, they can be generalized to the slowly varying ωde. Thus, these analytic forms of the scale factor, y, and ζ provide a very accurate and useful tool for measuring the properties of DE.

Growth index with the exact analytic solution of sub-horizon scale linear perturbation for dark energy models with constant equation of state

Abstract 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 [1] . 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 ⩽ z ⩽ 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.

Stable, time dependent, exact solutions for brane models with a bulk scalar field

We derive two classes of brane-world solutions arising in the presence of a bulk scalar eld. For static eld congurations, we adopt a time-dependent, factorizable metric ansatz that allows for radion stabilization. The solutions are characterized by a non-trivial warping along the extra dimension, even in the case of a vanishing bulk cosmological constant, and lead to a variety of inflationary, time-dependent solutions of the 3D scale factor on the brane. We also derive the constraints necessary for the stability of these solutions under time-dependent perturbations of the radion eld, and we demonstrate the existence of phenomenologically interesting, stable solutions with a positive cosmological constant on the brane.

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

There have been the approximate analytic solution [V. Silveira and I. Waga, Phys. Rev. D 50, 4890 (1994).] and several approximate analytic forms [W. J. Percival, Astron. Astrophys. 443, 819 (2005).][S. M. Carroll, W. H. Press, and E. L. Turner, Annu. Rev. Astron. Astrophys. 30, 499 (1992).][S. Basilakos, Astrophys. J. 590, 636 (2003).] of the growth factor

Constraints on scalar-tensor theories of gravity from observations

{D}_{g}

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

for the general dark energy models with the constant values of its equation of state

PALATINI f(R) COSMOLOGY

{\ensuremath{\omega}}_{\mathrm{de}}

Cosmic birefringence fluctuations and cosmic microwave background B -mode polarization

after Heath found the exact integral form of the solution of