More Limits On The Dark Matter Parameter Space

There may not be much of a consensus on what causes dark matter phenomena, but the evidence regarding what cannot be dark matter continues to mount.

Galaxy clusters, employed by Zwicky to demonstrate the existence of dark matter, pose new stringent tests. If merging clusters demonstrate that dark matter is self-interacting with cross section σ/m∼2 cm2/gr, MACHOs, primordial black holes and light axions that build MACHOs are ruled out as cluster dark matter. Recent strong lensing and X-ray gas data of the quite relaxed and quite spherical cluster A1835 allow to test the cases of dark matter with Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac distribution, next to Navarro-Frenck-White profiles. Fits to all these profiles are formally rejected at over 5σ, except in the fermionic situation. The interpretation in terms of (nearly) Dirac neutrinos with mass of 1.61+0.19−0.30 eV/c2 is consistent with results on the cluster A1689, with the WMAP, Planck and DES dark matter fractions and with the nondetection of neutrinoless double β-decay. The case will be tested in the 2018 KATRIN experiment.

Theodorus Maria Nieuwenhuizen "Subjecting dark matter candidates to the cluster test" (October 3, 2017).

Notably, the paper argues that the self-interaction effects observed in galaxy clusters rules out sterile warm dark matter candidates.

The paper also dismissed modified gravity theories arguing that they don't fit the galaxy cluster data, but the two references cited to that effect actually fail to show that is true for theories other than MOND. There are, in fact, other modified gravity theories that do deal accurately with galaxy clusters.