Tuesday, May 03, 2016

A new dark matter solution?

Speculative theories of gravity are a dime a dozen on arXiv, and I don't usually pay that much attention to them (well, they are hard to understand); but I am interested to see that there are two recent papers up, one by a handful of European physicists, and another by a couple of Japanese ones, talking about a bimetric theory of gravity that incorporates something that makes sense as a dark matter particle.  Here's the European abstract:
Observational evidence for the existence of Dark Matter is limited to its gravitational effects. The extensive program for dedicated searches has yielded null results so far, challenging the most popular models. Here we propose that this is the case because the very existence of cold Dark Matter is a manifestation of gravity itself. The consistent bimetric theory of gravity, the only known ghost-free extension of General Relativity involving a massless and a massive spin-2 field, automatically contains a perfect Dark Matter candidate. We demonstrate that the massive spin-2 particle can be heavy, stable on cosmological scales, and that it interacts with matter only through a gravitational type of coupling. Remarkably, these features persist in the same region of parameter space where bimetric theory satisfies the current gravity tests. We show that the observed Dark Matter abundance can be generated via freeze-in and suggest possible particle physics and gravitational signatures of our bimetric Dark Matter model.
You heard it here first.  Probably.

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