Dark matter was first hypothesized to exist in the 1930s when Fritz Zwicky made the observation that Einstein’s field equations for gravity demand an extra element to explain the rotational speeds of galaxies.
This extra element is dark matter, thought to comprise four fifths of the observable universe and to prevent galaxies from tearing themselves apart due to their centrifugal forces.
Now collaboration from Wuppertal University, Eotvos University of Budapest and Forschungszentrum Julich have come together to use Julich’s JUQUEEN supercomputer to create a profile of dark matter. The team, who published their research in the journal Nature, has profiled dark matter to consist of tiny particles of a mass between 50-1500 micro-electronvolts, up to ten billion times smaller than the electron.
These particles, called Axions, are the best candidate for dark matter so far and this revelation about their lightness explains, for example, why the LUX experiment (Large Underground Xenon experiment) has as yet been unable to detect them (as they were looking for ‘heavy Axion’ candidates). This means that the only possible avenue for their detection at the moment is with the use of particle accelerators such as the LHC at CERN. Since physicists are looking for particles beyond the ‘standard model’ of particle physics it may be possible within a few years to detect these tiny particles, given a boost to the sensitivity of their instruments. There may also be indications from CERN that there are particles beyond the standard model in light of their discovery of a heavier counterpart to the Higgs boson whose role is currently unknown.
The existence of Axions is also predicted by lattice quantum-chromodynamics (l-QCD), an extension to the theory governing the strong nuclear interaction, the force that keeps atomic nuclei together. Ordinary QCD predicts that there are topological quantum fluctuations which affect time-reversibility symmetry, meaning that certain processes occur differently depending on whether time is running forwards or backwards. The lattice extension to QCD solves this problem with the introduction of Axions, these are thought to produce quantum gravitational effects in the strong interaction and, in doing so, maintain the invariance of the time-reversibility symmetry, meaning that the time-reversibility symmetry doesn’t vary in the new model. The deeper implication is that the search for Axions will also play a role in the search for a theory of quantum gravity.