Cosmology Talks: Mateja Gosença & Bodo Schwabe on Simulating Mixed Fuzzy and Cold Dark Matter
It’s been too long since I shared one of those interesting cosmology talks on the Youtube channel curated by Shaun Hotchkiss. This channel features technical talks rather than popular expositions so it won’t be everyone’s cup of tea but for those seriously interested in cosmology at a research level they should prove interesting.
Anyway, although I’ve been too busy to check out the talks much recently I couldn’t resist sharing this one not only because it’s on a topic I find interesting (and have worked on) but also because one of the presenters (Mateja Gosença) is a former PhD student of mine from Sussex! So before I go fully into proud supervisor mode, I’ll just say that the talk is about AxioNyx, which is a new public code for simulating both ultralight (or “Fuzzy”, so called because its Compton de Broglie wavelength is large enough to be astrophysically relevant) dark matter (FDM) and Cold dark matter (CDM) simultaneously. The code simulates the FDM using adaptive mesh refinement and the CDM using N-body particles.
P. S. The paper that accompanies this talk can be found on the arXiv here.
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In the Dark 
November 12, 2020 at 1:28 pm
Hi Peter,
I think you are referring to the de Broglie, not the Compton wavelength
November 14, 2020 at 8:12 pm
As FDM comprises bosons I’m surprised that it’s not called fuzzy dark energy. Has any astrophysics been done on ultralight fermions with significant de Broglie wavelength?
November 15, 2020 at 9:20 am
Thanks. I had been taking the dark matter/dark energy terminology to refer to fermions/bosons rather than positive/negative pressure. Got a reference for fuzzy dark fermions?
November 15, 2020 at 11:31 am
It is possible for light bosonic fields to exert negative pressure so they can in principle generate a form of dark energy as well as dark matter.
The key thing about dark matter is that it has to cluster. With a bosonic particle this is no problem but for fermions you have to take account of the exclusion principle. Very light particles will pick up huge velocities if they are packed in at high spatial density. Neutrinos of course are fermions (with masses around the eV) and they are termed Hot Dark Matter because of this effect. You can’t make them cluster on galaxy scales because of this effect. Any fermionic dark matter candidate would have to be quite massive to get around this and can’t therefore be fuzzy.
November 16, 2020 at 11:02 am
Is the Peebles book “Cosmology’s Century”? How technical is it?
November 17, 2020 at 10:20 am
Interesting; thanks.