Direct detection of Planck mass WIMPs?

[jcap]

Are the current dark matter detection experiments sensitive to Planck mass WIMPs?

I've just looked at the Wikipedia WIMP article. It shows the excluded parameter space for the CDMS experiment with WIMP-nucleon cross section vs WIMP mass curves but they only go up to a WIMP mass of 1000 GeV.

 

[Vanadium 50]

First, there is nothing magical about the Planck mass.

Second, since the dark matter mass density is known (1/3 of a proton mass per cc), the heavier each individual particle is, the fewer of them are out there to detect. Long before you get to the Planck mass, you have too few particles to have a decent chance of spotting one.

Third, the weaker the interaction, the fewer particles were produced in the early universe. To get the sorts of low number densities implied by heavy particles means they interact very weakly indeed, which also makes them very hard to detect.

 

[Orodruin]

Third, the weaker the interaction, the fewer particles were produced in the early universe. To get the sorts of low number densities implied by heavy particles means they interact very weakly indeed, which also makes them very hard to detect.

A thermal relic becomes more abundant the weaker it interacts due to falling out of equilibrium earlier and therefore getting less Boltzmann suppressed. A very strongly interacting species would remain in thermal equilibrium longer and if the freeze-out temperature is much lower than its mass the Boltzmann suppression becomes very large.

That being said, it is unclear whether a particle of such a large mass as the Planck mass would ever be in thermal equilibrium to start with. It would more likely already be decoupled at the reheating temperature and therefore not really be produced in the early Universe. In such a situation, you will instead have a freeze-in mechanism, for which it is true that a weaker interaction gives a lower final density.

 

[Vanadium 50]

I also doubt something that heavy is in equilibrium.

Maybe here's a better way to express my thinking: detectable heavy dark matter has built-in contradictions. For example, if it interacts strongly, it will clump - and we know it doesn't. And/or it overcloses the universe. And it doesn't do that either.