Supercomputer provides new clues to find dark matter

Scientists have used supercomputer calculations to predict the properties of the mysterious dark matter - a particle that is believed to make up almost 85 per cent of the entire mass of the universe.
Researchers extended the successful Standard Model of particle physics which allowed them to predict the mass of so-called axions, promising candidates for dark matter.
Led by Professor Zoltan Fodor of the University of Wuppertal in Germany and Eotvos University in Hungary, they carried out calculations on Julich Research Centre's supercomputer JUQUEEN (BlueGene/Q).
"Dark matter is an invisible form of matter which until now has only revealed itself through its gravitational effects. What it consists of remains a complete mystery," said Andreas Ringwald, from DESY, a research institute in Germany.

Evidence for the existence of this form of matter comes, among other things, from the astrophysical observation of galaxies, which rotate far too rapidly to be held together only by the gravitational pull of the visible matter.
High-precision measurements using the European satellite "Planck" show that almost 85 per cent of the entire mass of the universe consists of dark matter.

All the stars, planets, nebulae and other objects in space that are made of conventional matter account for no more than 15 per cent of the mass of the universe.
The unknown form of matter can either consist of comparatively few, but very heavy particles, or of a large number of light ones, researchers said.

The searches for heavy dark-matter candidates using large detectors in underground laboratories and particle accelerators are still going on, but have not turned up any dark matter particles so far.
A range of physical considerations make extremely light particles, dubbed axions, very promising candidates. Using experimental setups, it might even be possible to detect direct evidence of them, researchers said.
"However, to find this kind of evidence it would be extremely helpful to know what kind of mass we are looking for," said Ringwald.
The results show, among other things, that if axions do make up the bulk of dark matter, they should have a mass of 50 to 1,500 micro-electronvolts, expressed in the customary units of particle physics, and thus be up to ten billion times lighter than electrons.

This would require every cubic centimetre of the universe to contain about ten million such ultra-lightweight particles.
Dark matter is not spread out evenly in the universe, however, but forms clumps and branches of a weblike network. Due to this, our local region of the Milky Way should contain about one trillion axions per cubic centimetre.
Thanks to the Julich supercomputer, the calculations now provide physicists with a concrete range in which their search for axions is likely to be most promising.
"The results we are presenting will probably lead to a race to discover these particles," said Fodor.
The findings were published in the journal Nature.