Technology Review - 26 April 2010
the physics arXiv blog
A CoGeNT confirmation of the DAMA signalIf dark matter exists it may take the form of mirror planets, mirror stars and mirror galaxies. Now one physicist says the most recent evidence seems to confirm this idea.
When astronomers study distant galaxies, they see only a small fraction of the mass needed to hold these clumps of stars together. Without some kind of extra hidden mass, galaxies ought to fly apart.
Astronomers call this hidden mass 'dark matter' and physicists around the world are engaged in an increasingly desperate race to find evidence of it here on Earth. That's why there are more than 30 experiments in various parts of the planet looking for the stuff.
The consensus is that, despite this global effort, dark matter remains well hidden. Nobody has had a whiff of the stuff.
That is nobody except an Italian group which has spent the last ten years or so watching a giant lump of sodium iodide. Their thinking is that any dark matter hitting the sodium iodide should generate a photon. And that as Earth moves around the Sun, they should see more photons when heading into the background sea of dark matter than when moving away from it.
Sure enough, this seasonal signal is exactly what this team says it sees. They claim that it's experiment called DAMA/LIBRA is the first direct evidence of dark matter.
The trouble is that nobody else believes them, mainly because so many other experiments have seen nothing. The critics says something else must be responsible for these seasonal signals, perhaps some kind of environmental change like a variation in temperature.
Then, about a month ago, everything changed when an experiment called CoGent based in the US reported that it too had found a hint of dark matter. CoGent looks for evidence that dark matter particles have bumped into a crystal of germanium and sure enough, the CoGent team say that the experiment is producing abundant evidence of these kinds of collisions.
Curiously, while most experiments are looking for relatively heavy dark matter particles which should produce higher energy collisions, CoGent looks for much lighter particles.
The interesting thing is that the DAMA\LIBRA evidence is from a similar mass range.
- arXiv.org > hep-ph > arXiv:1004.1424 > 08 April 2010
Implications of CoGeNT and DAMA for Light WIMP Dark MatterThe CoGeNT collaboration has recently reported a rising low energy spectrum in their ultra low noise germanium detector. This is particularly interesting as the energy range probed by CoGeNT overlaps with the energy region in which DAMA has observed their annual modulation signal. We show that the mirror dark matter candidate can simultaneously explain both the DAMA annual modulation signal and the rising low energy spectrum observed by CoGeNT. This constitutes a model dependent confirmation of the DAMA signal and adds weight to the mirror dark matter paradigm.
- arXiv.org > hep-ph > arXiv:1003.0014 > 05 April 2010 (v2)
In this paper, we study the recent excess of low energy events observed by the CoGeNT collaboration, and discuss the possibility that these events originate from the elastic scattering of a light (m_DM ~ 5-10 GeV) dark matter particle. We find that such a dark matter candidate may also be capable of generating the annual modulation reported by DAMA, as well as the small excess recently reported by CDMS, without conflicting with the null results from other experiments, such as XENON10. A dark matter interpretation of the CoGeNT and DAMA observations favors a region of parameter space that is especially attractive within the context of Asymmetric Dark Matter models. In such models, the cosmological dark matter density arises from the baryon asymmetry of the universe, naturally leading to the expectation that m_DM ~ 1-10 GeV. We also discuss neutralino dark matter from extended supersymmetric frameworks, such as the NMSSM. Lastly, we explore the implications of such a dark matter candidate for indirect searches, and find that the prospects for detecting the neutrino and gamma ray annihilation products of such a particle to be very encouraging.