Can we distinguish between dark energy and modified gravity?

by Dr Domenico SAPONE (U. of Geneva)

Wednesday 11 Jun 2008, 11:00 → 12:00 Europe/Zurich

1/1-025 (CERN)

There is now strong observational evidence that the expansion of the universe is accelerating. The standard explanation invokes an unknown ``dark energy'' component. But these models are faced with serious theoretical problems, which has led to increased interest in models where instead General Relativity is modified in a way that leads to the observed accelerated expansion. The question then arises whether the two scenarios can be distinguished. It was shown in M. Kunz & D. Sapone, PRL 98:121301, 2007 astro-ph/0612452 that this may not be so easy, with an explicit proof that a generalised dark energy model can match the growth rate of the DGP model. Many papers appeared after this work testing the consistency of General Relativity. In particular we will focus our attention on two particular works:

• B. Jain & P. Zhang, astro-ph/0709.2375
• Y. S. Song & K. Koyama, astro-ph/0802.3897

where it is stated that it is instead possible to distinguish at first order perturbation theory between modified gravity theories and dark energy models, providing a consistency check for General Relativity.