Friday, December 7, 2018

Lone Direct Dark Matter Detection Signal Contradicted

There have been many direct dark matter detection experiments. Just one of them, DAMA, claims to have seen a signal (purportedly at 9 sigma significance) of dark matter in the form of an annual modulation of events (some background events are expected anyway, but it shouldn't vary seasonally).

A new experiment, COSINE-100 attempted to replicate DAMA's finding using the same materials and theoretical framework which it reported upon in the journal Nature. The result contradicts the outlier positive signal from DAMA:
We observe no excess of signal-like events above the expected background in the first 59.5 days of data from COSINE-100. Assuming the so-called standard dark-matter halo model, this result rules out WIMP–nucleon interactions as the cause of the annual modulation observed by the DAMA collaboration. The exclusion limit on the WIMP–sodium interaction cross-section is 1.14 × 10−40 cm2 for 10-GeV c−2WIMPs at a 90% confidence level.
Once again, the dark matter paradigm has failed to show results and this result is a step backward for that theory with the only positive evidence for dark matter detection rejected as unsound.

Sabine discusses the result.


neo said...

whats your fav candidate for dark matter particle?

personally i think the most parsimonious explanation is micro black holes (on order of 10^19ev) + MOND

no need to extend the SM, except masses for neutrinos (dirac or majorna)

websterling said...

10^19 eV = 16000 grams. A black hole with this mass has a lifetime of 3.4e-13 seconds. So, not a good DM candidate.

neo said...

assuming that it can continue to decay, which some QG says is not the case.

websterling said...

Do you have any references for this?

Just wondering how this would work- Would black holes not evaporate? Would they only evaporate to some limiting mass/volume/temperature? Or something else?

neo said...

Black holes in quantum theories of gravity
It is possible, in some theories of quantum gravity, to calculate the quantum corrections to ordinary, classical black holes. Contrarily to conventional black holes, which are solutions of gravitational field equations of the general theory of relativity, quantum gravity black holes incorporate quantum gravity effects in the vicinity of the origin, where classically a curvature singularity occurs. According to the theory employed to model quantum gravity effects, there are different kinds of quantum gravity black holes, namely loop quantum black holes, non-commutative black holes, asymptotically safe black holes. In these approaches, black holes are singularity-free

Mitchell said...

In the literature, the end state of black hole evolution is sometimes called a "remnant".

Actually every theory that has evaporating black holes has some kind of final objects. It's just that in some theories, the "final objects" are simply a bunch of ordinary particles, whereas in other theories, the final objects are more exotic, like non-evaporating micro black holes.

There may even be theories which are somehow intermediate between these two cases. Already in string theory, black holes can be a lot like charged, very heavy solitons. What's the difference between a micro black hole that doesn't evaporate, and a very heavy elementary particle? Especially if the "particle" is something like a GUT monopole, a topologically stable soliton in the elementary fields.

So it's quite conceivable (at least to me) that there are black hole final states which consist e.g. of a big family of massive, stable, gauge-theoretic topological solitons. I believe the real problem in describing the end of black hole evaporation, has to do with space-time structure. Classically, a singularity forms but it is hidden behind the event horizon. Semiclassically, the event horizon shrinks to nothing, exposing the singularity. Is the singularity the remnant, a permanent space-time defect? Or is a quantum black hole singularity-free? Even string theorists haven't answered these questions to their own satisfaction.