The expansion of the Universe was proposed and observed by Lemaître and Hubble at the beginning of last century. The observation of the cosmic microwave background, the radiation left over from the Big Bang, confirmed this model as the reference model. The recent discovery of the acceleration of this expansion indicates that the content of the Universe is different from what was expected: only 4.4% of the total mass and energy of the Universe is visible, with the 95.6% missing being dark matter (21%) and dark energy (74%).
The nature of dark matter is totally unknown: its vast majority should be a new kind of matter, different to all the matter found up to now. The main candidates proposed by theories are axions, massive sterile neutrinos and WIMPs (weakly interacting massive particles), including the LSPs (lightest supersymmetric particles), whose natural candidate would be the neutralinos.
Determining the nature of dark matter is one of the main topics of modern cosmology and high energy physics, with huge impact on our understanding of the Universe.
Detecting dark matter is a complex task: it involves huge detection mass, very low detection thresholds, an excellent control of the detector background, and a cosmic background well below one event a day, something only possible in very deep underground laboratories.
The detection techniques used are based on noble gases in liquid state (allowing an excellent discriminating power from signal to noise), or detectors operating at ultra low temperatures (where one detects the effect of the interaction on the cooled material), trying to detect a dark matter particle interaction. The installation of similar detectors in ANDES will furthermore conduce to technology transfers in state-of-the-art technology.
Furthermore, an indirect way to detect dark matter is to find a modulation caused by the movement of the Earth in the halo of dark matter. There has been a strong controversy in the community about this signal, which could be faked by atmospheric effects. By being located in the southern hemisphere, ANDES could unambiguously discriminate the two scenarios.