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792 results on '"Nojiri S"'

102. Inflationary universe from perfect fluid and F (R) gravity and its comparison with observational data

Author

Bamba K., Nojiri S., Odintsov S., and Sáez-Gómez D.

Subjects
General Relativity and Quantum Cosmology
Abstract

© 2014 American Physical Society. We investigate the descriptions for the observables of inflationary models, in particular, the spectral index of curvature perturbations, the tensor-to-scalar ratio, and the running of the spectral index, in the framework of perfect fluid models and F(R) gravity theories through the reconstruction methods. Furthermore, the perfect fluid and F(R) gravity descriptions of inflation are compared with the recent cosmological observations such as the Planck satellite and BICEP2 experiment. It is demonstrated with explicit examples that perfect fluid may lead to the inflationary universe consistent with the Planck data. It is also shown that several F(R) gravity models, especially, a power-law model gives the best fit values compatible with the spectral index and tensor-to-scalar ratio within the allowed ranges suggested by the Planck and BICEP2 results.

Published
2014

110. Modified gravity: walk through accelerating cosmology

Author

Bamba, K., Nojiri, S., and Sergei Odintsov

Subjects
High Energy Physics - Theory, General Relativity and Quantum Cosmology, Cosmology and Nongalactic Astrophysics (astro-ph.CO), High Energy Physics - Theory (hep-th), FOS: Physical sciences, General Relativity and Quantum Cosmology (gr-qc), Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

We review the accelerating (mainly, dark energy) cosmologies in modified gravity. Special attention is paid to cosmologies leading to finite-time future singularities in $F(R)$, $F(G)$ and $\mathcal{F}(R,G)$ modified gravities. The removal of the finite-time future singularities via addition of $R^2$-term which simultaneously unifies the early-time inflation with late-time acceleration is also briefly mentioned. Accelerating cosmology including the scenario unifying inflation with dark energy is considered in $F(R)$ gravity with Lagrange multipliers. In addition, we examine domain wall solutions in $F(R)$ gravity. Furthermore, covariant higher derivative gravity with scalar projectors is explored., 16 pages, no figure, to appear in: Proceedings of the 7th Mathematical Physics Meeting: Summer School and Conference on Modern Mathematical Physics (Sept. 9--19, 2012, Belgrade, Serbia). Editors B. Dragovich and Z. Rakic. Published by Institute of Physics, Belgrade 2013, Serbia

Published
2013

116. Cosmological viability of f(R)-gravity as an ideal fluid and its compatibility with a matter dominated phase

Author

Salvatore Capozziello, Nojiri, S., Odintsov, S. D., Troisi, A., Capozziello, Salvatore, S., Nojiri, S. D., Odintsov, and A., Troisi

Subjects
High Energy Physics - Theory, Nuclear and High Energy Physics, General Relativity and Quantum Cosmology, High Energy Physics - Theory (hep-th), Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics
Abstract

We show that f(R)-gravity can, in general, give rise to cosmological viable models compatible with a matter-dominated epoch evolving into a late accelerated phase. We discuss the various representations of f(R)-gravity as an ideal fluid or a scalar-tensor gravity theory, taking into account conformal transformations. We point out that mathematical equivalence does not correspond, in several cases, to the physical equivalence of Jordan frame and Einstein frame. Finally, we show that wide classes of f(R)-gravity models, including matter and accelerated phases, can be phenomenologically reconstructed by means of observational data. In principle, any popular quintessence models could be "reframed" as an f(R)-gravity model., 11 pages, 1 figure

Published
2006

119. ITPA genetic variants influence efficacy of PEG‐IFN/RBV therapy in older patients infected with HCV genotype 1 and favourable IL28B type

Author

Matsuura, K., primary, Tanaka, Y., additional, Watanabe, T., additional, Fujiwara, K., additional, Orito, E., additional, Kurosaki, M., additional, Izumi, N., additional, Sakamoto, N., additional, Enomoto, N., additional, Yatsuhashi, H., additional, Kusakabe, A., additional, Shinkai, N., additional, Nojiri, S., additional, Joh, T., additional, and Mizokami, M., additional

Published
2013
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130. 1171 IDENTIFICATION OF GENETIC VARIANTS OF THE IL28B ASSOCIATED WITH SPONTANEOUS CLEARANCE OF HEPATITIS C VIRUS IN JAPANESE POPULATION

Author

Matsuura, K., primary, Tanaka, Y., additional, Nishida, N., additional, Sugiyama, M., additional, Kurosaki, M., additional, Izumi, N., additional, Tamori, A., additional, Abe, K., additional, Sugauchi, F., additional, Nojiri, S., additional, Joh, T., additional, Tsubouchi, H., additional, Tokunaga, K., additional, Ito, K., additional, and Mizokami, M., additional

Published
2010
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136. The Evaluation of Quality of Life by the Short-Form 36 Health Survey (SF-36) in Patients with Obstuructive Sleep Apnea Hypopnea Syndrome (OSAHS), Who Use Continuous Positive Airway Pressure (CPAP) for Long Term.

Author

Nojiri, S, primary, Yumino, Y, additional, Minagawa, S, additional, Kojima, J, additional, Numata, T, additional, Kinoshita, A, additional, Kawaishi, M, additional, Araya, J, additional, Nakayama, K, additional, Nomoto, Y, additional, Chiba, S, additional, and Kuwano, K, additional

Published
2009
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142. Delicate f(R) gravity models with a disappearing cosmological constant and observational constraints on the model parameters

Author

Dev, Abha, Jain, Deepak, Jhingan, S., Nojiri, S., Sami, M., and Thongkool, I.

Abstract

We study the f(R) theory of gravity using the metric approach. In particular we investigate the recently proposed model by Hu and Sawicki; Appleby and Battye; and Starobinsky. In this model, the cosmologicalconstant is zero in flat space time. The model passes both the solar system and the laboratory tests. But the model parameters need to be fine-tuned to avoid the finite time singularity recently pointed to in the literature. We check the concordance of this model with the H(z) and baryon acoustic oscillation data. We find that the model resembles the ΛCDM at high redshift. However, for some parameter values there are variations in the expansion history of the universe at low redshift.

Published
2008

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