Yesterday a short little letter filled with equations broke my brain with science. Researchers Xavier Calmet and Folkert Kuipers have a new work accepted into the journal Physics Letters B, and in it, they work out new limits on the mass of individual particles of dark matter.
As the name implies, dark matter is stuff that doesn’t interact with or emit light. It makes up about 27% of the universe, and because it only seems to interact via gravity, it is super hard to understand.
According to Calmet:
This is the first time that anyone has thought to use what we know about quantum gravity as a way to calculate the mass range for Dark Matter. We were surprised when we realised no-one had done it before – as were the fellow scientists reviewing our paper.
What we’ve done shows that Dark Matter cannot be either ‘ultra-light’ or ‘super-heavy’ as some theorise – unless there is an as-yet unknown additional force acting on it. This piece of research helps physicists in two ways: it focuses the search area for Dark Matter, and it will potentially also help reveal whether or not there is a mysterious unknown additional force in the universe.
The limits they derived put the mass-energy of any dark matter particles between 10-3 eV and 10^7 eV. To put this in context with other particles, they find dark matter should have masses in the same range as the various masses of neutrinos or electrons.
This consistency with neutrino masses is particularly tantalizing to me. While not discussed in this paper, many researchers have wondered if the annoyingly difficult to observe neutrino could be related to or a form of dark matter. This work doesn’t rule out that possibility.
To get at these limits, Calmet and Kuipers considered factors such as how fast would particles of different sizes decay? How big must it be to not require additional forces? And even what limits are created by high school chemistry concepts like the Pauli Exclusion Principle. While this is a very elegant paper, it does have limits. At the most simplistic level, there could be physics at play that we don’t know about, and some of the assumptions they made, such as quantum gravity following the traditional Plank scale, could be wrong.
But this is the first step, and this first step seems to confirm that dark matter can be explained with known physics as a particle of reasonable size and that we just may be following the right path toward its discovery.
The University of Sussex press release
“Theoretical bounds on dark matter masses,” Xavier Calmet and Folkert Kuipers, 2021 March 10, Physics Letters B