The h Bar

12:45 AM

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Currently it requires a reputation of 50 points or more to post comments to other users' posts. This creates some problems for new users : Instead of commenting they are tempted to post "answers" which are nothing more than comments. These have to be reviewed and/or flagged for deletion. Instea...

Secret

3:53 AM

According to a recent newscientist (vol 233, issue 3109) the dark matter experiments looks quite grim recently, with troubles verifying some observations from the DAMA experiments as well a large number of dark matter models were being ruled out.

It would not be surprising that if this trend continues even when the scheduled detectors were built in 2019, that MOND might be gaining acceptance

O wow, and now they are modelling superfluid black holes? I wonder how much complex can black holes get

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dmckee

4:19 AM

@Secret The current and near future "dark matter" detectors are actually WIMP detectors.

Secret

Is axion a type of WIMP?

dmckee

Certainly MOND will attract at least a little passing attention again but the covariance issue looks to be very hard, while dark matter has other candidates (starting with massive sterile neutrinos and axions and goin on from there) in the wings.

@Secret Last I hear the axion experiments were only at test bed scale. That is zero expectation of seeing anything, just proving that we can get the noise in the detector low enough that it would be able to see something if built to scale.

And scaling up is likely to be expensive. Though usually the costs come down a little between the first test beds and actually getting funding simply because technology advances.

Secret

I see, seems these are still at its infancy, in that case there are still a lot of dark matter candidates yet to be tested.

dmckee

If WIMPs, supersymmetry, axions and heavy sterile neutrinos all fail you start getting into some fairly exotic theories, and I get the feeling that those don't have widespread enthusiasm. And I really do think that even WIMPs not showing up will drive some people back to considering modified gravity scenarios.

I'm trying to remember some of the speculative talks I've seen. I think that if lose more than a couple of the current dark matter candidates we get into a situation where the leptogenesis picture becomes harder to justify and that opens a lot of doors that wouldn't be considered while more "natural" theories are still on the table.

Secret

As far I know, for WIMPS, it is basically similar to how that issue of newscientist said, it looks grim with a large swarth of models being ruled out and only a thin band left behind to be tested

LHC still have not seen any signs of supersymmetry, and some said some supersymmetry above the MSSM were ruled out or constrainted based on that

For sterile neutrinos, I recalled last year, ICECUBE's non detection of them ruled out at least one of the models

I don't have much info about axion experiments though, the latest news about it is a calculation that suggest we can use toroidal magnets i…

For micro blackholes, I don't recall any gamma ray events nor lensing observations to date being associated with them, despite for ordinary or large black holes, CHANDRA (or maybe another detector) found there are a lot of them, as one of Johnrennie's starred message in a previous chat message shown

dmckee

4:56 AM

You don't detect sterile neutrinos. Because they don't interact weakly (which is what 'sterile' means). You constrain the mixing matrix for the active flavors and ask how much room there is for non-unitarity.

I haven't been following that story closely, but the constraints (which had been ridiculously loose for a long time because $\theta_{13}$ was such a mystery) have tightened up enough that you have to jump through some hoops to arrange enough mixing to sterile neutrinos early enough in the history of the universe to agree with the BAO studies.

But this story won't be nailed down until the mass hierarchy question is settled. That train is rounding the corner and coming into to view, but it is not here yet.

DanielSank

5:52 AM

Hi, everybody.

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