EAS Publications Series

Issue		EAS Publications Series Volume 36, 2009 Dark Energy and Dark Matter: Observations, Experiments and Theories
Page(s)		211 - 212
DOI		10.1051/eas/0936030
Published online		30 May 2009

Dark Energy and Dark Matter: Observations, Experiments and Theories
E. Pécontal, T. Buchert, Ph. Di Stefano and Y. Copin (eds)
EAS Publications Series, 36 (2009) 211-212
DOI: 10.1051/eas/0936030

Matter density fluctuations in the running $\Lambda$ CDM and $\Lambda$ XCDM models

J. Grande¹, R. Opher², A. Pelinson¹ and J. Solà¹

¹ High Energy Physics Group, Dept. ECM, and Institut de Ciències del Cosmos, Univ. de Barcelona, Barcelona, Catalonia, Spain
² IAG, Univ. de São Paulo, São Paulo, SP, Brazil

Published online: 30 May 2009

Abstract
We have investigated the matter density fluctuations, $\delta_M(a)$ , in the running $\Lambda$ CDM and $\Lambda$ XCDM models. The latter was proposed as an interesting solution to the cosmic coincidence problem. It includes an extra dynamical component, the “cosmon” X, which interacts with a running $\Lambda$ , but not with matter. Adopting a dark energy (DE) “picture”, in which the total DE and matter components are conserved separately, the growth of density fluctuations ${\cal G}(a)=\delta_M(a)/a$ can be written in terms of the effective equation of state. We made use of the measured galaxy fluctuation power spectrum, $P_{\rm GG}$ , and of the linear bias parameter $b^2(z=0)=P_{\rm GG}/P_{\rm MM}$ , where $P_{\rm MM}\propto \delta_M^2$ is the matter power spectrum of the model under consideration. According to the 2dFGRS survey, $b^2_{\Lambda}(z\simeq 0)=1$ within a $10\%$ accuracy for the $\Lambda$ CDM model. We adopted this limit to put constraints on the fundamental parameter, $\nu$ , of the running $\Lambda$ CDM model. We found an agreement with previous estimates obtained by a number of different methods and authors. This provided a good test of the procedure, which we used then to determine the physical region of the $\Lambda$ XCDM parameter space.

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Matter density fluctuations in the running CDM and XCDM models

Matter density fluctuations in the running $\Lambda$ CDM and $\Lambda$ XCDM models