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A scale-invariant spectrum of isocurvature perturbations is generated during collapse in the ekpyrotic scaling solution in models where multiple fields have steep negative exponential potentials. The scale invariance of the spectrum is realized by a tachyonic instability in the isocurvature field. This instability drives the scaling solution to the late… (More)

We compute the non-Gaussianity of the curvature perturbation generated by ekpyrotic collapse with multiple fields. The transition from the multi-field scaling solution to a single-field dominated regime converts initial isocurvature field perturbations to an almost scale-invariant comoving curvature perturbation. In the specific model of two fields, φ1 and… (More)

- S Mizuno
- Nihon Jibiinkoka Gakkai kaiho
- 1970

A scalar field has played a very important role in cosmology. The problems of the standard Big-Bang theory, such as the horizon, and flatness problems could be resolved by the inflationary scenario [1]. In this scenario, the universe expands quasi-exponentially because of the vacuum energy, whose origin in many models are given by a scalar field (inflaton).… (More)

The new result on the QSO absorption lines from VLT-UVES sample is compared with the past reports on the time-variability of the fine-structure “constant” derived from the Keck/HIRES observation, on the basis of an oscillatory behavior of the scalar field supposed to be responsible for the cosmological acceleration.

According to recent observations, the existence of the dark energy has been considered. Even though we have obtained the constraint of the equation of the state for dark energy (p = wρ) as −1 ≤ w ≤ −0.78 by combining WMAP data with other astronomical data, in order to pin down w, it is necessary to use other independent observational tools. For this… (More)

We study cosmological perturbations in the brane models with an induced Einstein-Hilbert term on a brane. We consider an inflaton confined to a de Sitter brane in a five-dimensional Minkowski spacetime. Inflaton fluctuations excite Kaluza-Klein modes of bulk metric perturbations with mass m = −2(2l− 1)(l+ 1)H and m = −2l(2l+ 3)H where l is an integer. There… (More)

We explore the initial conditions for cosmological N-body simulations suitable for calculating the higher-order cumulants of the density field. In general, the initial conditions based on the perturbation theory (PT) provide incorrect growth in next leading order, which are called transients. Before transients have been completely suppressed compared with… (More)

We explore the possibility of putting constraints on dark energy models with statistical property of large scale structure in the non-linear region. In particular, we investigate the w dependence of non-Gaussianity of the smoothed density distribution generated by the nonlinear dynamics. In order to follow the non-linear evolution of the density… (More)

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