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 bane 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 Λ = 0 cosmology to an observer in the brane which satisfies standard cosmological constraints including the 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 ΛCDM cosmology. Its influence, however, is offset by the dark-radiation term. Possible additional observational tests of this new cosmological paradigm are suggested.

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

We investigate the big-bang nucleosynthesis in a Brans-Dicke model with a varying Λ term using the Monte-Carlo method and likelihood analysis. It is found that the cosmic expansion rate differs appreciably from that of the standard model. The produced abundances of 4 He, D, and 7 Li are consistent with the observed ones within the uncertainties in nuclear reaction rates when the baryon to photon ratio η = (5.47−6.64) × 10 −10 , which is in agreement with the value deduced from WMAP.

We constrain the thermal evolution of the universe with a decaying cosmological term by using the method of the analysis for the Wilkinson Microwave Anisotropy Probe (WMAP) observation data. The cosmological term is assumed to be a function of the scale factor that increases toward the early universe, and the radiation energy density is lower compared to that in the model with the standard cosmological constant (ΛCDM). The decrease in the radiation density affects the thermal history of the universe; e.g. the photon decoupling occurs at higher-z compared to the case of the standard ΛCDM model. As a consequence, a decaying cosmological term affects the cosmic microwave background (CMB) anisotropy. Thanks to the Markov-Chain Monte Carlo method, we compare the angular power spectrum in the decaying ΛCDM model with the CMB data, and we get severe constraints on parameters of the model. PACS numbers: 95.36.+x, 98.80.Es