Report on the Workshop ‘Varying Fundamental Constants’

http://www.lorentzcenter.nl/lc/web/2009/358/info.php3?wsid=358

Motivation & Aims

The deepest enigma of modern physics is whether or not there are any fundamental scalar fields in nature. Although there are widely accepted theories in particle physics and cosmology which rely on them, neither side has so far produced any direct and definitive evidence. On the other hand, Einstein gravity does not contain any scalar fields. This is a very remarkable fact, because almost any consistent gravitational theory that one can think of will have them.

Recent developments suggest that scalar fields are just as important in cosmology. Among other roles, they are the preferred explanation for the recently claimed variations of what have been considered fundamental constants of nature. Varying fundamental constants directly map the dynamics of the underlying cosmological scalar fields, and the large redshift lever arm afforded by a range of observational techniques in astrophysics and cosmology combined with  local laboratory measurements can be used to optimally probe gravity on large and small scales, as well as providing crucial indirect clues on the presence of extra dimensions and ultimately string theory itself.

Varying fundamental constants are part of ESA and ESO science drivers for next generation of facilities, so closer interactions between theorists, observational astronomers, cosmologists and atomic physicists will be crucial for progress in the field. There are controversial claims of a 5-sigma detection of a smaller value of the fine-structure constant, and of a 3-sigma detection of a larger value of the electron-to-proton mass ratio, which are contradicted by analyses of other groups. Meanwhile laboratory measurements find null results, as do other astrophysical probes. Given the potential implications, it is important to shed light on this controversy. Confirmation of these variations would immediately imply a violation of the Einstein Equivalence Principle, signalling the breakdown of the concept of gravity as geometry and pointing to undiscovered gravitational physics.

We planned the workshop with the aim of bringing together representatives from the key groups working on this topic, to devise a strategy for a thorough inter-disciplinary study of varying constants, combining theoretical expectations and predictions, astrophysical observations (from the ground and space) and local experiments (mostly with atomic clocks, either in ground laboratories or in microgravity). A specific goal was the discussion of a proposal for a European research network on this topic.

The Workshop & Outcomes

There were a total of 46 registered participants, of which 20 were students or young post-docs. Given the goals of the meeting, we had a series of review talks in the mornings (10 in total – one of the scheduled reviewers cancelled at the last minute and it proved impossible to replace him), while in the afternoons were split into tutorials for the junior participants and discussion sessions for the senior participants.

Broadly speaking the first morning was devoted to particle physics and cosmology aspects, the second to astrophysical observations (the subject of the ongoing controversy) and the third to local laboratory measurements. The tutorials (each lasting a total of 3 hours) also addressed each of these three areas.

The review talks and tutorials have almost all been recorded, and the audio files are available on the workshop web-page together with pdf versions of the presentation slides. The quality of the recordings was very high and we would like to suggest to the Lorentz Center staff to encourage others to do the same, since it provides a unique service to the rest of the academic community in The Netherlands and elsewhere.

The interaction between researchers and students coming from different areas was extremely fruitful, and was greaitly aided by the friendly atmosphere of the Lorentz Center. The workshop allowed the participants to gain a deeper understanding of the key issues at the forefront of research in this emerging field, as well as of the strengths and weaknesses of the European community as a whole. This was crucial for the discussions of future Eruopean-wide activities.

The main outcome of the workshop was the decision to submit a proposal in reply to the ESF call for EUROCORES Research Themes. The orgnizational details were decided during the three days of the workshop, and a significant part of the proposal was also written there. This proposal has now been submitted, and we await its outcome in the fall.

Final Remarks

We are most grateful for the generous finacial support of the Lorentz Center, and particularly for agreeing to host the workshop at fairly short notice. The fact that such an ideal venue is available and can organize things very quickly as an opportunity suddenly arises is one of the great strengths of the Lorentz Center. The workshop would not have been possible without the help, constructive suggestions and support of Henriette Jensenius, Martje Kruk and Corrie Kuster through the various stages of the organization. We look forward to new developments in this emerging field, and to discussing them again in the future at the Lorentz Center.

Carlos Martins (CAUP, Porto, Portugal)

Jarle Brinchmann (Leiden Sterrewacht, the Netherlands)