On the full quantum trispectrum in multi-field DBI inflation (2009)
Mizuno, Shuntaro, Arroja, Frederico, Koyama, Kazuya
We compute the leading order connected four-point function of the primordial curvature perturbation coming from the four-point function of the fields in multi-field DBI inflation models. We confirm...
Lorentz boost and non-Gaussianity in multi-field DBI-inflation (2009)
Mizuno, Shuntaro, Arroja, Frederico, Koyama, Kazuya, Tanaka, Takahiro
We show that higher-order actions for cosmological perturbations in the multi-field DBI-inflation model are obtained by a Lorentz boost from the rest frame of the brane to the frame where the brane...
On the full trispectrum in single field DBI-inflation (2009)
Arroja, Frederico, Mizuno, Shuntaro, Koyama, Kazuya, Tanaka, Takahiro
We compute the tree-level connected four-point function of the primordial curvature perturbation for a fairly general minimally coupled single field inflationary model, where the inflaton's...
Dynamics of a scalar field in Robertson-Walker spacetimes (2009)
Copeland, Edmund J., Mizuno, Shuntaro, Shaeri, Maryam
We analyze the dynamics of a single scalar field in Friedmann-Robertson-Walker universes with spatial curvature. We obtain the fixed point solutions which are shown to be late time attractors. In...
Non-gaussianity from the bispectrum in general multiple field inflation (2008)
Arroja, Frederico, Mizuno, Shuntaro, Koyama, Kazuya
We study the non-gaussianity from the bispectrum in multi-field inflation models with a general kinetic term. The models include the multi-field K-inflation and the multi-field Dirac-Born-Infeld...
Constraints on scalar-tensor models of dark energy from observational and local gravity tests (2008)
Tsujikawa, Shinji, Uddin, Kotub, Mizuno, Shuntaro, Tavakol, Reza, Yokoyama, Jun'ichi
We construct a family of viable scalar-tensor models of dark energy (DE) which possess a phase of late-time acceleration preceded by a standard matter era, while at the same time satisfying the local...
Non-Gaussianities from ekpyrotic collapse with multiple fields (2007)
Koyama, Kazuya, Mizuno, Shuntaro, Vernizzi, Filippo, Wands, David
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...
Tatekawa, Takayuki, Mizuno, Shuntaro
We explore the initial conditions for cosmological N-body simulations suitable for calculating the skewness and kurtosis of the density field. In general, the initial conditions based on the...
Curvature perturbations from ekpyrotic collapse with multiple fields (2007)
Koyama, Kazuya, Mizuno, Shuntaro, Wands, David
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...
Non-Gaussianity of the density distribution in accelerating universes II:N-body simulations (2006)
Tatekawa, Takayuki, Mizuno, Shuntaro
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...
Inflaton perturbations in brane-world cosmology with induced gravity (2006)
Koyama, Kazuya, Mizuno, Shuntaro
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...
Non-Gaussianity of the density distribution in accelerating universes (2005)
Tatekawa, Takayuki, Mizuno, Shuntaro
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 ($p = w \rho$) as $-1...
Correspondence between Loop-inspired and Braneworld Cosmology (2005)
Copeland, Edmund J., Lidsey, James E., Mizuno, Shuntaro
Braneworld scenarios are motivated by string/M-theory and can be characterized by the way in which they modify the conventional Friedmann equations of Einstein gravity. An alternative approach to...
Slow-roll corrections to inflaton fluctuations on a brane (2005)
Koyama, Kazuya, Mizuno, Shuntaro, Wands, David
Quantum fluctuations of an inflaton field, slow-rolling during inflation are coupled to metric fluctuations. In conventional four dimensional cosmology one can calculate the effect of scalar metric...
BPS pp-wave brane cosmological solutions in string theory (2005)
Tanabe, Makoto, Mizuno, Shuntaro
We construct time dependent BPS pp-wave brane solutions in the context of M-theory and type II supergravity. It is found that N-brane solutions we considered satisfy the crossing rule as S-brane...
Generalised cosmological scaling solutions (2004)
Copeland, Edmund J., Lee, Seung-Joo, Lidsey, James E., Mizuno, Shuntaro
Motivated by the recent interest in cosmologies arising from energy density modifications to the Friedmann equation, we analyse the scaling behaviour for a broad class of these cosmologies comprised...
Cosmological evolution of general scalar fields in a brane-world cosmology (2004)
Mizuno, Shuntaro, Lee, Seung-Joo, Copeland, Edmund J.
We study the cosmology of a general scalar field and barotropic fluid during the early stage of a brane-world where the Friedmann constraint is dominated by the square of the energy density. Assuming...
$\Delta\alpha/\alpha$ from QSO absorption lines driven by an oscillating scalar field (2004)
Fujii, Yasunori, Mizuno, Shuntaro
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...
Effective Gravitational Equations on Brane World with Induced Gravity (2003)
Maeda, Kei-ichi, Mizuno, Shuntaro, Torii, Takashi
We present the effective equations to describe the four-dimensional gravity of a brane world, assuming that a five-dimensional bulk spacetime satisfies the Einstein equations and gravity is confined...
Dynamics of Scalar field in a Brane World (2002)
Mizuno, Shuntaro, Maeda, Kei-ichi, Yamamoto, Kohta
We study the dynamics of a scalar field in the brane cosmology. We assume that a scalar field is confined in our 4-dimensional world. As for the potential of the scalar field, we discuss three...
Quintessence in a Brane World (2001)
Mizuno, Shuntaro, Maeda, Kei-ichi
We reanalyze a new quintessence scenario in a brane world model, assuming that a quintessence scalar field is confined in our 3-dimensional brane world. We study three typical quintessence models :...
Tsujikawa, Shinji, Maeda, Kei-ichi, Mizuno, Shuntaro
We study brane-world preheating in massive chaotic inflationary scenario where scalar fields are confined on the 3-brane. Assuming that quadratic contribution in energy densities dominates the Hubble...