Everything you didn’t want to know about WIMPs but have been forced to find out.

The waning of the WIMP

101 pages, 20 figures.

mollwollfumble said:

Everything you didn’t want to know about WIMPs but have been forced to find out.

The waning of the WIMP

101 pages, 20 figures.

I don’t understand this as well as I thought I would. To summarise a few points:

1) Dark matter particles may be scalar, fermionic or vector. Whatever that means.

2) Dark matter could be detected in three different ways – bouncing off normal matter, particle + antiparticle annihilation, creation in the LHC.

3) There are three different ways that WIMPs could be produced in the LHC: directly, by decay of the Higgs, or by decay of the Z boson.

4) The two main unknowns are mass and strength of interaction.

5) The size of the particle + antiparticle annihilation cross section determines the density of WIMPs in the present universe.

6) The article talks about “Portals”. These are the regions on a chart of mass vs strength_of_interaction than have not yet been ruled out by dark matter searches. Results from the Planck Space Telescope strongly constrain the mass of WIMPs to be within a few GeV of 60 GeV. This is the only mass for which the interaction with normal matter can be weak enough to have escaped current dark matter searches. By comparison, the Higgs has a mass of 160 GeV and the Z boson has a mass of 91 GeV.

7) The future dark matter searches include XENON1T and LZ experiments. If these fail to detect dark matter then almost all possibilities present in the simplest mathematical models of dark matter will be ruled out.

Pfft all the cool kids are talking about emergent gravity now. No DM or DE

Dropbear said:

Pfft all the cool kids are talking about emergent gravity now. No DM or DE

That’s the postmodern approach – if you can’t make it work, resurrect somebody else’s 50 year old idea.

mollwollfumble said:

Dropbear said:

Pfft all the cool kids are talking about emergent gravity now. No DM or DE

That’s the postmodern approach – if you can’t make it work, resurrect somebody else’s 50 year old idea.

Maybe theres a reason no one can “make it work”

Dropbear said:

mollwollfumble said:

Dropbear said:

Pfft all the cool kids are talking about emergent gravity now. No DM or DE

That’s the postmodern approach – if you can’t make it work, resurrect somebody else’s 50 year old idea.

Maybe there’s a reason no one can “make it work”

Quite so. WIMPs are getting closer and closer to being eliminated by observation. Hence the article title “The Waning of the WIMP”.

Perhaps they are shy and self conscious?

The absolute epitome of next generation Dark Matter (WIMP) detectors is called LZ.

A complete technical design summary report of LZ has just appeared on the web.

https://arxiv.org/pdf/1703.09144.pdf

… identify this dark matter through sensitive terrestrial direct detection experiments. Failing to detect a signal would rule out most of the natural parameter space that describes WIMPs.

In the following sections, we introduce the cosmological and particle physics evidence pointing to the hypothesis that the dark matter
is composed of WIMPs, detectable through nuclear recoil (NR) interactions. We then give the motivation for a massive liquid xenon (LXe) detector as the logical next step in the direct detection of dark matter.

Very weakly interacting cold dark matter (CDM), particles moving nonrelativistically, appear to be an essential ingredient in the evolution of structure in the universe. N-body simulations of CDM can explain much of the structure, ranging from objects made of tens of thousands of stars to galaxy clusters.

While we know much about the impact of dark matter on a variety of astrophysical phenomena, we know very little about its nature. An attractive conjecture is that dark matter particles were in equilibrium with ordinary matter in the hot early universe. Thermal equilibrium describes the balance between annihilation of dark matter into ordinary particle-antiparticle pairs, and vice versa. As the universe expanded and cooled, the reaction rates eventually fell below the level required for thermal equilibrium, leaving behind a relic abundance of dark matter.

Models of supersymmetry (SUSY) predict the neutralino, a new particle that has properties appropriate to be a WIMP. Astrophysical measurements show that dark matter behaves like a particle and not like a modification of gravity … in particular the Bullet cluster.

WIMP detection experiments, compared to supersymmetry predictions.

Great graph