An hour ago, Physics World decided to promote a paper claiming that dark matter may have already been seen:
Dark Matter with Pseudoscalar-Mediated Interactions Explains the DAMA Signal and the Galactic Center Excessalthough the readers who have memorized all 1 million preprints at arXiv.org know very well that the identical paper was submitted under a different title,
October 2013, LUX has pretty much won the "dark matter is not seen" war and excluded lots of theories with light dark matter particles that were suggested by the positive experiments from the opposing alliance in the war.
However, DAMA – an old team that has claimed the observation of dark matter – claims that they still see their signal whose significance has grown above 9 sigma. Their signal depends on seasons – it is maximized in June and minimized in December. Others are convinced that the right interpretation of this annual modulation has to be mundane and unrelated to dark matter.
The (not quite) new PRL paper by Eugenio Del Nobile and two collaborators, Arina and Panci, claims that they can still explain the DAMA signal by a model where the dark matter interaction with the nuclei proceeds via an intermediate pseudoscalar particle, an axion, if you wish. Its mass should be comparable to an \(\MeV\). Meanwhile, the dark matter particle itself is between \(20\) and \(40\GeV\). But the uncertainty about most parameters seems to be large.
Their model circumvents the simple spin-independent form of the interactions that is apparently excluded by the other, negative experiments, while it predicts a large enough signal for DAMA and it offers an explanation for the Galactic center excess of gamma rays around \(1\)-\(3\GeV\). Del Nobile and pals stress that the experimenters should start to more explicitly articulate their assumptions about the dark matter interactions that they are excluding.
Juan Collar of the "dark matter is seen" experiment CoGeNT thinks that a simpler way to reconcile the positive results from DAMA with the negative results from others is to assume that DAMA sees the interactions of the dark matter with the electrons rather than nuclei.
Lots of questions concerning the detection of the dark matter particle remain confusing...