Large-scale structure and the Cardassian fluid

¹ School of Mathematical Science, Queen Mary, University of London, Mile End road, London E1 4NS, UK e-mail: steph.fay@gmail.com
² Laboratoire Univers et Théories (LUTH), UMR 8102, Observatoire de Paris, 92195 Meudon Cedex, France
³ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway e-mail: morad@astro.uio.no

Received: 3 February 2006
Accepted: 24 August 2006

Abstract

In this paper, we confront the predictions of the power law Cardassian model for the baryon power spectrum with the observations of the SDSS galaxy survey. We show that they fit only for very unusual values of the cold dark matter or baryon density parameters, the Hubble parameter or the spectral index of the initial power spectrum. Moreover, the best-fit Cardassian models turn out to be phantom models. If one wants to recover the usual values for these constants, as quoted by the WMAP team, the power law Cardassian model turns out to be indistinguishable from a ΛCDM model.