Cosmology of ghost-free bimetric gravity: a consistent modified-gravity alternative to dark energy
* SPEAKERS
Name
Affiliation
E-mail
Yashar Akrami
University of Olso
* HOST(Applicant)
Name
Affiliation
E-mail
Arman Shafieloo
APCTP
arman(at)apctp.org
* DATE / TIME
2013-06-11, 16:30PM
* ABSTRACT
The idea of Dark Energy has now been around for about 15 years after the striking discovery of the late-time acceleration of the Universe from the measurements of distant supernovae. Despite its excellent agreement to various cosmological data, the simplest explanation of the cosmic acceleration by assuming a nonzero, but small, cosmological constant has been strongly debated, mainly due to the unprecedented difficulties in theoretically justifying the value of the constant from the current understanding of how the Universe works at microscopic levels. Many alternative explanations have now been proposed in which the acceleration is a consequence of cosmic evolution of some unknown dynamical field, called Dark Energy. While this assumption is yet to be tested observationally using the existing and forthcoming high-quality cosmological observations, an alternative approach based on modifications of Einstein\\\\\\\\\\\\\\\'s theory of gravity has also been considered recently. In this talk, I will focus on the cosmological implications of one of such interesting modifications in which gravity becomes massive in a theoretically consistent way. The model is based on a recently proposed theory of massive gravity in which the gravitational sector is extended by adding an extra spin-2 particle and the theory is free of ghost instabilities. I will show how the model can explain the late-time acceleration without any need to an explicit cosmological constant. The model will be compared to the standard $\\\\\\\\\\\\\\\\Lambda$CDM model using background dynamics and state-of-the-art statistical techniques, and the parameters of the model will be estimated accordingly. Finally generalizations of the model, in particular when the extra two-tensor of the theory also couples to matter giving the first consistent \\\\\\\\\\\\\\\"bimetric theory of gravity\\\\\\\\\\\\\\\", and prospects for placing stronger constraints on the model parameters from upcoming data and perturbative analyses will be discussed.
