Riou Nakamura

Observational constraints on accelerating brane cosmology with exchange between the bulk and brane

We explore observational constraints on a cosmological brane world scenario in which the bulk is not empty. Rather, exchange of mass energy between the bulk and the brane is allowed. The evolution of matter fields to an observer on the brane is then modified due to new terms in the energy-momentum tensor describing this exchange. We investigate the constraints from various cosmological observations on the flow of matter from the bulk into the brane. Interestingly, we show that it is possible to have a {lambda}=0 cosmology to an observer in the brane which satisfies standard cosmological constraints including the cosmic microwave background (CMB) temperature fluctuations, Type Ia supernovae at high redshift, and the matter power spectrum. This model even accounts for the observed suppression of the CMB power spectrum at low multipoles. In this cosmology, the observed cosmic acceleration is attributable to the flow of matter from the bulk to the brane. A peculiar aspect of this cosmology is that the present dark-matter content of the Universe may be significantly larger than that of a {lambda}CDM cosmology. Its influence, however, is offset by the dark-radiation term. Possible additional observational tests of this new cosmological paradigm are suggested.

Big-Bang nucleosynthesis: Constraints on nuclear reaction rates, neutrino degeneracy, inhomogeneous and Brans-Dicke models

We review the recent progress in the Big-Bang nucleosynthesis which includes the standard and nonstandard theory of cosmology, effects of neutrino degeneracy, and inhomogeneous nucleosynthesis within the framework of a Friedmann model. As for a nonstandard theory of gravitation, we adopt a Brans–Dicke theory which incorporates a cosmological constant. We constrain various parameters associated with each subject.

Big-Bang Nucleosynthesis in comparison with observed helium and deuterium abundances: possibility of a nonstandard model

Comparing the latest observed abundances of 4He and D, we make a ?2 analysis to see whether it is possible to reconcile primordial nucleosynthesis using up-to-date nuclear data of NACRE II and the mean-life of neutrons. If we adopt the observational data of

Constraint on Heavy Element Production in Inhomogeneous Big-Bang Nucleosynthesis from the Light Element Observations

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Brans-Dicke model constrained from the Big Bang nucleosynthesis and magnitude redshift relations of supernovae

He by Izotov et al., we find that it is impossible to get reasonable concordance against the standard Big-Bang nucleosynthesis. However, including degenerate neutrinos, we have succeeded in obtaining consistent constraints between the neutrino degeneracy and the baryon-to-photon ratio from detailed comparison of calculated abundances with the observational data of

Cosmic microwave background constraints on a decaying cosmological term related to the thermal evolution

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CMB constraints on the thermal evolution with a decaying cosmological term

He and D: the baryon-to-photon ratio in units of

Constraints on a Vacuum Energy from Both SNIa and CMB Temperature Observations

10^{-10}

Constraints on the heavy elements production in inhomogeneous Big‐Bang nucleosynthesis from light‐element observations

is found to be in the range 6.02 <

On the Origin of Dark Energy in Brane World Cosmology

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