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Thread: Is Dark Matter Equivocal

  1. #61
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    Quote Originally Posted by kzb View Post
    From what I read it is only detectable from above the atmosphere. Perhaps others can help.
    It is easiest to spot from orbit because the main features we look for (associated with electronic excitations) are in the UV. These are blocked by the atmosphere. They are also much easier to observe as absorption features which is a big limit on the objects and locations we can probe in this waveband. The quadrupole effects relating to molecular deformations are pretty faint and found in IR bands also partially attenuated by the atmosphere. In bands we can observe more easily the features tend to be almost continuum, very broad and not diagnostic. It is much easier to find if there are strong UV or X-ray sources nearby or if it is collisionally excited in shock fronts. Luckily environments like this are relatively common, which allows us to probe these examples and set limits on how general the halos can be to match observations.

    Ground based detections are possible but challenging. And for areas without something increasing the signature (shocks, UV) the detection limit is poor, I believe it is not good enough to unequivocally probe the proposed hydrogen halos. I think SOFIA might have a relevant IR capability too, so airborne measurements are probably possible.

    Edit to add: The James Webb telescope should help bound possibilities - the spectrometer it has covers a relevant part of the IR spectrum.

  2. #62
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    Quote Originally Posted by Shaula View Post
    It is easiest to spot from orbit because the main features we look for (associated with electronic excitations) are in the UV. These are blocked by the atmosphere. They are also much easier to observe as absorption features which is a big limit on the objects and locations we can probe in this waveband. The quadrupole effects relating to molecular deformations are pretty faint and found in IR bands also partially attenuated by the atmosphere. In bands we can observe more easily the features tend to be almost continuum, very broad and not diagnostic. It is much easier to find if there are strong UV or X-ray sources nearby or if it is collisionally excited in shock fronts. Luckily environments like this are relatively common, which allows us to probe these examples and set limits on how general the halos can be to match observations.

    Ground based detections are possible but challenging. And for areas without something increasing the signature (shocks, UV) the detection limit is poor, I believe it is not good enough to unequivocally probe the proposed hydrogen halos. I think SOFIA might have a relevant IR capability too, so airborne measurements are probably possible.

    Edit to add: The James Webb telescope should help bound possibilities - the spectrometer it has covers a relevant part of the IR spectrum.
    Thanks for this, it seems there is plenty of that "parameter space" left for a large amount of molecular hydrogen to exist.

    The James Webb telescope may have the capabilities but will anyone bother using it for this purpose? That is my complaint more than anything; if you don't look you don't see.

  3. #63
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    Quote Originally Posted by kzb View Post
    Thanks for this, it seems there is plenty of that "parameter space" left for a large amount of molecular hydrogen to exist.
    No problems.

    The size of the available parameter space is only large if you cherry pick what kinds of observations you will accept. But I'm not going to keep arguing this with you.

    Quote Originally Posted by kzb View Post
    The James Webb telescope may have the capabilities but will anyone bother using it for this purpose? That is my complaint more than anything; if you don't look you don't see.
    They probably will. They have used a lot of other instruments to try to do it, despite it being really hard. They have also looked for second and third order effects which are easier to observe. I really don't understand your complaint - they have looked and not seen it.

  4. #64
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    MOND or MOND-like?

    We know that GR is the more accurate theory compared to Newton. MOND suggests that at very low accelerations the inverse square law changes giving a dark matter effect. It already violates the SEP of GR. Could there be some other clues that suggest further differences?

    There are a few possible clues.

    One centers on the idea of the MOND radius. This is where, at sufficient distance from a mass, the Newtonian acceleration drops to MOND acceleration, a_0 = 1.2 X 10^(-10) m/sec^2.
    The usual equation is g = GM/R^2 where g is a_0. So for the sun, R is around 8000 A.U.. For a radius of 1 meter, the enclosed mass would be 1m^2X a_0/G ,a little under 1.8Kg. What is rarely considered is that there is a second inner MOND radius. Consider a spherical drop water of sufficiently low mass that the acceleration at its surface is a_0. Here M=(4/3)pi R^ 3 X Density(in Kg/m^3 units). With water at 997 Kg/m^3, R is .4307 millimeters. As the mass grows there will be separation between the outer and inner MOND radius. Inner R may shrink a bit as pressure increases density. Now, instead of water, consider a spherical crystal of Thallium doped NaI with a density of 3670 Kg/m^3. R is .117 millimeters.

    Cylinders of these crystals are used some dark matter detector experiments, most notably the DAMA-LIBRA experiment that sees a signal of over 9 sigma. There is tension with the XENON experiments that see no signal. There are experiments with some similarity to DAMA-LIBRA to try to replicate the results such as ANAIS and Cosine-100. If both experiments reproduce the DAMA results, then slight differences in set-up are of minor relevance. If one reproduces and the other not, a study of the differences in set-up may be informative. If both experiments fail to reproduce DAMA results, this does not need nullify DAMA but may represent control experiments where set-up differences are significant.

    Signals occur throughout the crystal but some of them suffer a veto. Signals from the central region tend to be passed.

    Today, ANAIS-112 released a preprint on the arxiv:
    Annual Modulation Results from Three Years Exposure of ANAIS-112

    https://arxiv.org/abs/2103.01175

    They say no to reproducing DAMA’s results. Cosine-100 early results could not make a claim to support DAMA or the null hypothesis.

    There is at least one set-up difference between DAMA and the other two. That is material used for shielding. In DAMA each crystal is encased in a pure form of copper; the detectors are placed in a copper box; copper bricks then surround the copper box as the outer shield. In the other two experiments the outer shield is lead, not copper.

    So the question is if there is a novel property of the transition metal, copper where a sufficient mass is needed to observe the DAMA signal? This would suggest control experiments. Replace copper bricks with lead to see if the signal disappears or replace lead with copper to acquire the signal.

    Perhaps there are other differences that need to be tested. There remains the question if the DAMA results are due to an as yet undiscovered systematic that passes muster of the Bernabei list.

    It should be noted that from the perspective of Classical MOND (1983) neither the outer nor inner MOND radius could play a role in the DAMA signal because of the relatively strong gravity due to the Earth, Moon, Sun, and even Jupiter would suppress or screen the MOND acceleration that announces the Dark Matter Effect. Even though the EFE of the galactic field into the stronger solar system has been discussed by Milgrom (2009), it is very small, on order of 10^-15m/sec ^2 at the extreme of MICROSCOPE’s sensitivity, this would have no bearing on DAMA.

    Should control experiments implicate copper as having a role in the DAMA signal other than just shielding this would be rather remarkable. It would be needed to be discovered how much and how distributed and whether this varies due to potential such as on the space station compared to near Earth surface.

    To implicate a MOND-like connection between the inner MOND radius and DAMA via a novel copper role might suggest the ability to descreen a field within the copper enclosure. The outer radius would still be screened and mass interior to the enclosure would regenerate sufficient acceleration to exceed a_0. At DAMA you have a thick layer of copper bricks but the interior copper box containing the detectors are too massive; interior to the copper box the detectors exceed 250 Kg which is too massive; each detector is enclosed in copper which is around 10 Kg which would also be too massive except for the central .117 millimeter radius slightly adjusted due to the fact that the crystals are cylinders rather than spheres.

  5. #65
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    In that summary from Borman, the data set in question is from scintillation (light) emitted by particles hitting the detectors which are shielded by rock underground, and massive metal faraday cages. The variation is measured as the Earth orbits the sun, and is a tiny signal. The experiment must presume the particles that can get through all that shielding (WIMPS or Neutralinos or ?) come from a dominant direction (our galactic centre?) . If these are the mysterious dark matter, why do we expect scintillation to occur? Conversely can we identify these particles by other experiments? It is interesting to speculate as Borman does about the shield nature. I have seen electrons tunnel through solid copper, they set up self focussing fields, but these would be higher energy electrons, and I do not know what secondary effects would be expected, apart from x rays. Lead is better at absorbing x rays but again I do not know the secondary radiation from that absorption. i do not offer any solutions, just musing on the questions raised by these conflicting experiments.
    Last edited by profloater; 2021-Mar-03 at 09:44 AM.
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  6. #66
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    Quote Originally Posted by profloater View Post
    If these are the mysterious dark matter, why do we expect scintillation to occur?
    If the are WIMPs then they interact via the weak force. Hence the scintillation detectors work the same way as for neutrinos. The difference is in the energy transfer per interaction - it should be larger for massive particles. Detection methods invlving momentum should be universal for weakly interacting particles. Other interactions may not be.
    https://en.wikipedia.org/wiki/Neutri...ion_techniques

    Note that this is only if they are WIMPS - which are one candidate for dark matter.

  7. #67
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    Probing Extragalactic Planets Using Quasar Microlensing

    https://iopscience.iop.org/article/1...41-8213/aaa5fb

    This is an about of quasar microlensing. A quasar viewed through an intervening galaxy shows many gravitational lensing episodes consistent with planetary-mass bodies. This is not the only study which has found this either. Quasars with no intervening galaxy do not show this phenomenon, indicating the microlensing is due to the intervening galaxy and not the quasar itself.

    This paper ascribes these events to unbound planets, at least 2000 unbound planets, Moon to Jupiter mass, per star. That 2000 is a lower bound, not an estimate of the actual figure.

    I think there is a problem with this unbound planet explanation. In active star formation regions, there have been censuses (?) of planetary-mass objects (PMOs) sensitive down to Jupiter mass. The PMOs are much less common than stars in all these studies.

    For smaller planets, the expectation is these would be formed by the planet formation mechanism, i.e. in orbit of a star (or brown dwarf). Models of planetary system formation often show that planets are ejected in the early days of the system. However I don't think any of them show that at least 2000 planets would be ejected from each system on average. More likely it is one or two.

    So that is my problem, microlensing showing thousands of unbound planets per star in a distant galaxy, but the evidence from our own galaxy saying that number is not feasible.

    Some say these unbound planets are actually the small gas clouds I mentioned upthread. At extragalactic distances they act as gravitational microlenses, like a planet. Closer to home they do not, because they are extended objects, and so microlensing is not detected at closer range.

    If they are not these small gas clouds, is it feasible there are thousands of unbound planets for every visible star in our galaxy?

  8. #68
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    So, what about this fifth force of nature?

    https://www.bbc.co.uk/news/56643677

    A fifth fundamental force might help explain some of the big puzzles about the Universe that have exercised scientists in recent decades.

    Could this be effectively MOND under another name?

  9. #69
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    Give it time, and weíll see, but remember the fundamental problem with MOND is that nobody has managed to come up with a reasonable modification of gravity that fits all the evidence and works as well as just assuming matter that mostly interacts through gravity (dark matter).

    Incidentally, Iíve mentioned this in other threads, but there are fifth force claims every so many years. I was excited the first two or three times I heard such a claim - discovery of new physics would be wonderful - but the claims havenít worked out so far and now I just wait and see if they come up with something that is actually confirmed. If they do, thatís when Iíll get excited.

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  10. #70
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    Quote Originally Posted by kzb View Post
    So, what about this fifth force of nature?

    https://www.bbc.co.uk/news/56643677

    A fifth fundamental force might help explain some of the big puzzles about the Universe that have exercised scientists in recent decades.

    Could this be effectively MOND under another name?
    Not really - this is the old muon magnetic dipole issue. It's been around for at least a decade, this is just a much better measurement. There are several ways it could be explained - the 'fifth force' one is usually a force more akin to the weak force that changes the higher order hadronic contributions to the dipole moment (which is why we don't see this issue with predictions of the electron dipole moment).

    This result really doesn't have much, if anything, to do with low energy physics or the kinds of macroscale forces required to generate MOND like accelerations.

    Edit to add: Essentially they are conflating two completely different things in the article. There are 'fifth force' suggestions for cosmological problems as well but they are unlikely to be the same things as something that affects the magnetic dipole of the muon. If the force talked about in the article is real then the cosmological ones will have to be a sixth force.

  11. #71
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    More on the DAMA signal

    Cosine-100 released a paper on the arXiv yesterday:

    Strong constraints from COSINE-100 on the DAMA dark matter results using the same sodium iodide target
    https://arxiv.org/abs/2104.03537

    They do not see the DAMA signal.

    While the annual modulation hypothesis seemed consistent with the DAMA NaI and phase 1 DAMA LIBRA data, an issue arose with the phase 2 DAMA LIBRA data with respect to the 1-2 Kev range:

    Dark Matter implications of DAMA/LIBRA-phase2 results

    https://arxiv.org/abs/1804.01231

    With both ANAIS and COSINE not supporting the annual modulation, it may be time to review the basic data from DAMA with respect to whether the signal is a sine or a sawtooth suggesting the signal might be processing artifact.

    Annual modulations from secular variations: relaxing DAMA?

    https://arxiv.org/abs/2002.00459

    Perhaps the same approach can be used in support of the mis modeling hypothesis for the quasi annual (355 day) signal of the Pioneer spacecraft.

    Meanwhile, a couple weeks ago,in version 2, a possible role for Copper appears in the Eotvos Pattern. A re-analysis of the 1922 paper suggests a non-zero slope. If not a WEP violation, perhaps a WIMP wind is being sensed as a hypothesis.

    Significance of Composition-Dependent Effects in Fifth-Force Searches
    https://arxiv.org/abs/2012.02862

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