The nature of the astronomical dark matter or the hunt for eluding species
Tuesday 21 October 2014
to 14:30 at
Pierre Salati (LAPTh)
The Universe contains an almost evanescent component whose nature is still unresolved. The so-called astronomical dark matter was discovered in 1933 by Fritz Zwicky, who showed that the Coma cluster of galaxies was much heavier than initially guessed from its luminosity. Since then, refined and numerous observations have confirmed Zwicky’s discovery : galaxies and their clusters behave like gigantic icebergs.
Cosmological observations indicated moreover that the nature of dark matter is exotic. This component is not made of ordinary atoms. Among the plethora of possible candidates that have been so far proposed, weakly-interacting and massive particles (WIMPs) are one of the most exciting possibilities. These elementary species, whose existence is predicted by the extensions of the Standard Model of particle physics, are naturally produced in the early stages of the Big-Bang, with a relic abundance in agreement with the measurements of the Planck satellite.
I will briefly review the various experiments which are hunting for these dark matter particles underground, inside the polar cap and in orbit around the Earth. I will concentrate on the searches for antimatter cosmic rays, i.e., antiprotons and positrons. In that respect, the discovery in 2008 of an unexpected excess of high-energy positrons in the cosmic radiation raised the tremendous hope that WIMPs were not just a fantasy. Alas, although the anomaly is real and has been confirmed by the AMS-02 collaboration, it is interpreted, now that the dust has settled down, as a signal from nearby pulsars. I will conclude by summarizing the results collected at the large hadron collider (LHC) at CERN, and will discuss how they impact on the dark matter searches.