Does dark matter come in two types?

Published in Physics World, 8 Jun 2010

Contradictory results from experiments searching for dark matter can be resolved if the elusive dark stuff is made up of two types of particle, according to physicists in the US.

The new theory could clear up a mystery that came to light in 2008, when the PAMELA collaboration released one of the strongest pieces of evidence yet for the direct detection of dark matter – a substance thought to make up over 80% of the universe’s matter. PAMELA saw a bump in the abundance of cosmic anti-electrons, also known as positrons, thought to be generated as dark-matter particles annihilate. But there was no concordant signal for anti-protons, which should also be generated by the annihilation. […]

The rest of this article is available here.