Degenerate vacua as the origin of the dark energy

I propose a new mechanism to account for the observed tiny but finite dark energy in terms of a non-Abelian Higgs theory, which has infinitely many perturbative vacua characterized by a winding number, in the framework of inflationary cosmology without introducing any tiny numbers.Comment: To be published in Proc. the XVIIIth IAP meeting "On the Nature of Dark Energy.

Probing the star formation epoch with Wilkinson Microwave Anisotropy Probe (WMAP) data and high-redshift QSOs

Using the values of the cosmological parameters obtained from Wilkinson Microwave Anisotropy Probe (WMAP) and the cosmological chemical clock observed by high-redshift quasars, it is shown that star formation should have started by the redshift $z_F > 9.5$, and that $z_F$ is sensitive only to \omegamz h^2 in flat $\Lambda$CDM cosmology

Curvature perturbation at the local extremum of the inflaton's potential

The spectrum of curvature perturbation generated during inflation is studied in the case the inflation-driving scalar field (inflaton) $\phi$ crosses over its potential extremum. It is shown that the nondecaying mode of perturbation has a finite value and a proper formula is given. The result is also extended to more general cases where $\ddot{\phi}$ is non-negligible.Comment: 6 pages, 1 figure. To appear in Physics Letters

Sample Variance of the Higher-Order Cumulants of Cosmic Density and Velocity Fields

If primordial fluctuation is Gaussian distributed, higher-order cumulants of the cosmic fields reflect nonlinear mode coupling and provide useful information of gravitational instability picture of structure formation. We show that their expected deviation (sample variance) from the universal values is nonvanishing even in linear theory in the case where observed volume is finite. As a result, we find that the relative sample variance of the skewness of the smoothed velocity divergence field remains as large as $\sim 30$ even if the survey depth is as deep as $\sim 150h^{1}Mpc$.Comment: 8 pages including 1 figure, aas.te