Dark Energy Inflation w - -1 looks good still

Stéphane Ili?^1,2,*, Martin Kunz^2,3,†, Andrew R. Liddle^2,‡, and Joshua A. Frieman^4,5,§
¹Magistère de Physique Fondamentale, Université Paris-Sud XI, Orsay 91405, France
²Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, United Kingdom
³Département de Physique Théorique, Université de Genève, 1211 Geneva 4, Switzerland
⁴Fermilab Center for Particle Astrophysics, Batavia, Illinois 60510, USA
⁵Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, Illinois 60637, USA

Received 25 February 2010; published 3 May 2010

Traditionally, inflationary models are analyzed in terms of parameters such as the scalar spectral index n_s and the tensor to scalar ratio r, while dark energy models are studied in terms of the equation of state parameter w. Motivated by the fact that both deal with periods of accelerated expansion, we study the evolution of w during inflation, in order to derive observational constraints on its value during an earlier epoch likely dominated by a dynamic form of dark energy. We find that the cosmic microwave background and large-scale structure data is consistent with w_inflation=-1 and provides an upper limit of 1+w ? 0.02. Nonetheless, an exact de Sitter expansion with a constant w = -1 is disfavored since this would result in n_s=1.

Phys Rev D May 15, 2010