Research project P7/37 (Research action P7)
Understanding Fundamental Interactions: collaboration between research teams engaged in theoretical and experimental approaches.
Fundamental interactions include electroweak forces, strong interactions, and gravity (and their possible extensions). Their study aims at unraveling Nature’s mechanisms at their most intimate level, but should also provide understanding of our Universe and its evolution through work at the edge of present knowledge. This quest involves the most powerful experimental tools (notably CERN’s Large Hadron Collider) and means of observation (particularly in the quest for dark matter and multi-messenger astro- and cosmo-particles).
The previous phases of the IAP programme, involving most of the present teams (IAP V/27 and VI/11), have established tight collaboration between theorists and experimentalists. This was recognized with enthusiasm by a very thorough “ex-post” evaluation. The next five years will see crucial developments with key physics results expected:
- The LHC in Geneva is reaching its “cruising” stage, and should provide the first answers on the mode of realization of the Brout-Englert-Higgs mechanism (see below), probably already on the basis of data gathered by the end of 2012, before a shut-down which will decisively improve the capacities of the accelerator. In particular, this powerful and versatile tool will probe physics beyond the Standard Model, dark matter candidates, large extra dimensions…
- All over the world, experiments and observations focus on the nature of neutrino masses and mixings on the one hand, on direct and indirect dark matter searches on the other, with greatly increased sensitivity. While a timeline is harder to set, we are definitely entering an exciting era.
- Observational cosmology (in the long tradition of G.Lemaître), which includes the expected results of the Planck and gamma-ray satellites, but also high-energy cosmic ray/ neutrino detectors, such as Auger, TelescopeArray, IceCube and its extensions, is testing the detailed predictions of astrophysical and cosmological models with constantly increasing sensitivity. Dark matter, dark energy, the origin of high-energy cosmic rays are some of the key mysteries to be unraveled.
This period is also crucial for the operation of the Belgian research teams:
- A new generation of physicists, educated in the previous IAP periods, is taking a leading role not only in research, but also in planning collaborations and strategy for future quests: Most of our nodes have new managers, and 2 have been re-configured to stress the extended theoretical, phenomenological and experimental interaction around the LHC. These new managers do not come unprepared, and have already put their mark, notably in the “future experiments” workgroup of IAP VI, which studied roadmaps for future experiments for the Belgian teams – a key task which will be pursued with energy.
- In parallel with cutting-edge research, the need for collaboration at the training level was felt, and led to a series of initiatives in the previous networks: not only an impressive list of Master- and PhD-level courses (taught in English in the various institutions, which leads to considerable student exchange already at the Master level), but also more traditional Summer Schools, and conferences (such as the Moriond series, which pays special attention to the young scientists). The new network will systematize these training tools, and further advertise them.
- The tested structure of an “IAP board”, responsible for all hirings (at the PhD or Postdoc level) allows for more visibility, coordination, and ensures very high standards of recruiting. It has been commended by the exp-post evaluation, and will of course continue to play its role. While Work Package coordinators appeared spontaneously in the previous network, we plan to give them more prominence.
- In the brief description below, we evoke both the combined research approach, and the outstanding physics questions.
- Theory groups aim at establishing unified models, encompassing the known interactions. Both “deductive” and “inductive” methods are used. The “deductive” approach, quite typical of mathematical physics, rests on assumed symmetries to propose a compelling (and usually elegant) structure “from first principles” using the strong constraints placed by mathematical consistency, in particular the absence of uncontrollable divergences… From these very general structures (e.g., string theory, supergravity, or variants of General Relativity), the “observable” physics needs then to be deduced (often with new assumptions, e.g. the topological structure of extra dimensions). In particular, we are faced with the difficult endeavor of reconciling gravity with the other fundamental interactions within a quantum framework.
The “inductive” approach starts from (striking) experimental facts, such as the strong suppression of certain processes, the mass and mixing patterns of particles, the constraints on dark matter, to construct (usually less ambitious) unification models, including various possible extensions of the Standard Model of the strong, weak and electromagnetic interactions.
- In both cases, the models can only be validated by working out their experimental or observational consequences in great detail.
- One of the key tasks of the LHC will be to elucidate in which way the Brout-Englert-Higgs mechanism (which originated in our groups and is needed to unify electroweak interactions) is realized: will we find a single fundamental scalar, a more complicated structure involving dark matter, bound states or some new strong interaction...?
In this quest, strong interactions are to be dealt with. They are both a topic of study, through the interplay of theoretical and experimental approaches, and a background which needs to be assessed very precisely to extract the weaker processes of interest.
- The experimental groups work in large international collaborations, using the most powerful accelerators and the latest observational devices to gather the data needed to test such theories or to force a new approach. For the LHC, the Belgian teams have joined their efforts on the CMS detector, where many different analysis channels are explored (nature of the symmetry-breaking mechanisms, flavour physics with top quarks, search for particles beyond the Standard Model, large extra dimensions…). Flavour physics in the NA62 experiment (our participation is an offspring of the previous stage of IAP) also brings strong constraints on “new physics” models. Other domains of current experimentation involve neutrino physics (the long-baseline OPERA experiment near Rome detects neutrinos produced at CERN), neutrino astrophysics (IceCube is a km3 detector in the Antarctic ice, and also looks for indirect signals of dark matter), high-energy cosmic rays (Telescope Array, IceCube and its extensions). While the "hardware" part of the experimental activities is covered by other sources of funding (IISN, FWO), a considerable effort in the interpretation of data must be pursued.
- Beyond these experiments with direct involvement in the data taking, we also use the data from a number of other tests (direct or indirect dark matter searches, satellite experiments), and in particular participate in the data analysis of the Planck satellite telescope presently scrutinizing the Cosmic Microwave Background of our Universe.
The ultimate purpose is to improve our understanding of fundamental interactions; for this, we need
• to develop the potential of each group by additional means (mostly the international exchange of post-docs);
• to tighten the collaboration and links between the activities of the groups;
• to train a significant number of young scientists. Both excellence in their own area and a sound knowledge in the associated fields, as provided by this network, will allow them to make significant contributions to our understanding of physical laws.
Our foreign partners are chosen to support and strengthen the work of our consortium, both by their excellence in research and their contribution to the common organisation of high-level international meetings.
