Division Particle & Astroparticle Physics
 
 

Research: Dark Matter


The nature of Dark Matter (DM) and also of Dark Energy in the Universe are among the most exciting questions of astroparticle physics. Dark Matter and Dark Energy are actually the main constituents of the Universe as shown in Figure 1. The evidence for DM is based on the gravitational effects of this new form of matter, for example on the motion of visible stars, dust, or gas in galaxies (including the Milky Way), the motion of galaxies in clusters, the evolution of matter structure in the Universe, the temperature fluctuations in the cosmic microwave background, or Big Bang nucleosynthesis. A very active on-going experimental research program has a good potential for significant discoveries in the coming decade.

Figure 1: The composition of the known Universe: shown are the contributions from Dark Energy, Dark Matter and ordinary matter made of Standard Model particles.
The composition of the known
			Universe

Dark Matter is most likely composed of some type of particle which does not interact electromagnetically or strongly. However, it is a well motivated assumption that Dark Matter has in addition to gravity also some other (presumable weak) interaction with normal matter, i.e. is a Weakly Interacting Massive Particle (WIMP). Such particles are predicted by many extensions of the Standard Model, and in this case the abundance of Dark Matter particles is predicted to be in roughly the range required by observations due to thermal production in the early Universe. The WIMP hypothesis can be tested with three complementary methods: (a) search for the interaction of DM particles in underground detectors (``direct detection''), (b) search for the products of annihilations or decays of DM particles e.g., inside the sun, or at the centre of our galaxy (``indirect detection''), and (c) direct production of DM particles at high energy particle collider experiments. In a given model the strength of the signals in these three observational chanels can be related in principle, as illustrated in Figure 2. In all three of these avenues substantial experimental progress is expected within the next few years. The group performs phenomenological research relating possible signals, exploring the complementarity of the various observational channels, and constructing models able to explain all available data on Dark Matter.

Figure 2: Interaction of WIMP dark matter with Standard Model particles. In a given model for the cross sections relevant for thermal production in the early Universe, for indirect detection, for direct detection, and for production in collider experiments are related to each other.
WIMP Dark Matter detection

Many new projects for direct DM detection experiments are under way or in preparation (e.g., CDMS-II, XENON100, COUPP, PICASSO, ZEPLIN). The next generation of experiment aims at ton-scale detectors (e.g., SuperCDMS, EURECA, XENON, LUX, ArDM, WARP, DEAP). These experiments will improve the sensitivity for WIMP cross sections by 4-5 orders of magnitude with respect to current bounds, and cover most of the interesting parameter space of common DM models. In particular, Supersymmetric DM will be crucially tested. Within the group analyses of available data from DM direct detection experiments are performed, as well as prospective sensitivity studies for future experiments are carried out. This is done in close contact with the XENON group at in the same division. In indirect DM detection various techniques are explored to look for annihilation or decay products of DM, including cosmic ray experiments on satellites (e.g., EGRET, PAMELA, FERMI-LAT) or on balloon flights (e.g., ATIC, HEAT, PPB-BETS), atmospheric Cerenkov telescopes (HESS, MAGIC), or neutrino telescopes (SuperKamiokande, IceCube, ANTARES, KM3NET). Various signatures can be explored, such as high energetic anti-matter particles (positrons, anti-protons, anti-deuterons), gamma rays, radio emission, or high energy neutrinos. Many of these experiments are expected to deliver results within the next few years. The Large Hadron Collider (LHC) at CERN is at the focus of the high-energy physics community. This experiment is expected to shed light on physics at the energy scale of several 100~GeV, responsible for electro-weak symmetry breaking. Several arguments suggest that physics beyond the Standard Model should show up at that scale. Many models for this new physics (such as, e.g., Supersymmetry) offer a candidate particle for DM. Therefore, one may hope that results from LHC will provide another piece of information on the DM problem. Typically, DM will show up as missing energy in decay chains of heavy particles. This signature per se is rather indirect and it will be necessary to relate possible findings of this kind at LHC to signals from direct or indirect DM detection experiments, aiming at consistent interpretations in terms of DM by taking into account all available information from non-accelerator experiments. An important approach in the field of DM will be to combine data from direct searches, indirect detection, and collider experiments. This will be essential in order to gain confidence in a DM interpretation of any positive signal. All three experimental avenues towards DM identification will provide rather indirect and vague information. Therefore, exploring complementary data and performing consistency checks will be necessary. In a specific model it might be possible to obtain definite predictions for the various signatures of DM, and such models might be identified (or falsified) through combined analyses. Apart from WIMPs, there are also other very promising candidates for Dark Matter, such as axions, keV sterile neutrinos, gravitinos and others. In these cases experimental signatures can be very different, and the phenomenology of such candidates is explored within the group. Theoretical work in the field includes construction of models which predict the various dark matter candidates. The corresponding research covers classical WIMP candidates with new physics at the electroweak scale, as well as non-WIMP candidates. The ultimate goal will be to obtain a consistent theory beyond the Standard Model, which provides a DM particle in agreement with all available data.

 
 


Last modified: Mon 8. May 2017 at 14:54:02