The Dark Side of the Universe
FCOMP-01-0124-FEDER-015309 & PTDC/FIS/111725/2009
Carlos J. A. P. Martins
The deepest enigma of modern physics is whether or not there are any scalar fields in nature. They have long been part of the standard model of particle physics, most notably through the Higgs field, which is thought to be responsible for endowing the building blocks of matter with mass (as well as making the theory gauge-invariant). On the other hand, Einstein gravity does not make use of any scalar fields. This is a remarkable fact, because almost any consistent gravitational theory that one can think of (from Newtonian gravity to models with extra dimensions, such as string theory) will include them. The fact that the only gravitating field in the universe is a rank-two tensor (the metric) is, to some extent, what defines Einstein gravity.
Although cosmology has recently entered a precision era, this has come with a price that 96% of the contents of the universe are in a still unknown form. These developments also suggest that scalar fields are just as important in cosmology. They are preferred candidates to solve key puzzles, including the exponential expansion of the early universe (dubbed inflation) and the dark energy that is accelerating it again today. They might also contribute to the formation of structure in the universe and the possible variation of what been considered fundamental constants of nature.
So far scalar field searches have concentrated on accelerator experiments (of which the LHC is the latest example), but if they exist they should also have cosmological fingerprints. This project will identify and exploit crucial observational probes of the dark side of the universe and fundamental physics. Specifically we will search for evidence of cosmological scalar fields, providing the strongest constraints to date on their existence and properties, or possible a detection. The team is currently small but experienced and very active in the field and well connected internationally. With the further human resources being requested we will have a lasting impact on the field.
The project entails ground-br4aking work in three inter-related lines of research (dynamical dark energy, varying fundamental couplings and sources of non-gaussianity) and contributions to the next generation of space experiments such as ESA's Planck Surveyor and EUCLID and ground-bases instruments such as ESO's ESPRESSO and CODEX. Our key goals are:
- Obtain new, more precise measurements of the fine-structure constant alpha and the proton-to-electron mass ratio mu, through dedicated observations in the world's best telescopes, including a recently approved ESO Large Programme (PI: Paolo Molaro) and novel measurements with the PEPSI spectrograph at the LBT. We will improve on the precision of current measurements by a factor of 6-10, and developed the science case for future high-resolution ultra-stable spectrographs.
- Conducting feasibility studies for new probes, including methods to test the temperature-redshift relation and to use measurements of fundamental couplings as a probe of dark energy (a technique that has been developed by our team).
- Performing pioneering N-body and hydrodynamic simulations of a range of dynamical dark energy models, identifying observable differences and expertise that will be strategically crucial for a possible participation in future missions like EUCLID.
- Gaining better understanding of the cosmological sources of non-gaussianity, including cosmic superstrings networks, and studying their consequences on the cosmic microwave background and large-scale structure.
The international panel that carried out the 2007 evaluation of Portuguese research units fully recognized the research excellence of CAUP and our team (both in terms of our publication record and our network of international collaborators), while at the same time expressing concern about the shortage of human resources (which may prevent us from being internationally active in all our areas of expertise). This grant is a key step to resolve this situation.
Fundação para a Ciência e a Tecnologia
Start: 1 July 2011
End: 31 December 2014