Principal Investigator
Nelson J. Nunes

Abstract
The discovery, in 1998, that the Universe is currently undergoing an accelerated expansion is one of the greatest milestones in all physics. Naturally, over the last 15 years, many proposals to explain this evolution have been brought forward. Most ideas involve scalar field dark energy or extensions of Einstein’s gravity. These proposals are essentially phenomenological without any relation to each other. One major step forward was the realisation in 2011 that all this models are subclasses of the most general scalar-tensor theory that leads to second order equations of motion, the Horndeski Lagrangian.

The fundamental question we want to address in this project can be posed as:

What is the nature of dark energy and how does it couple to the rest of the world?

The innovative approach of this project is to start with the most general description, the Horndeski theory, and then narrow down the possibilities (i.e. functions and parameter space) by using simple theoretical considerations (existence of tracking and scaling solutions) and current observational data. (The common alternative instead, has been to test each and every model individually, which is far from ideal.) It also stands out by the range of data we apply, from cosmological observations to laboratory experiment results. The results will be extremely important to plan forthcoming missions, in that it allows us to understand the capabilities a mission has to unveil the nature of dark energy; its necessary time of data acquisition; and define its strategy of observation. These types of contributions are in high demand among the working packages of the Euclid mission.

Start
1 October 2016
End
29 December 2020

Funding Institution
Fundação para a Ciência e a Tecnologia