Indirect Darkness

So I’ve been hanging out at the Indirect and Direct Detection of Dark Matter conference this week, and been struck by several things.

It is a good meeting, enthusiastic crowd, definite excitement in the air.
It would have read much better if the title had been “Direct and Indirect Detection of Dark Matter”, but that would have been wrong…

This is not my usual turf, though I was on a couple of papers on the adiabatic contraction of collisionless matter during growth of supermassive black holes, which is a way to get very high dark matter densities (QHS95 and SHQ95).

Basically a “spike” in the density of dark matter develops around the black hole, if the growth of the black hole is suitably non-violent in a technical and plausible sort of way. And, actually, even if the black hole growth is violent the spike is still there, just not as sharp, and from a lower base density.

What really matters for the strength of the spike is what the “initial” distribution function of the dark matter is, “before” the black hole, if there is a “before”, and that goes back to cosmology and the formation of early structure. It also is tightly coupled to any dark matter physics.

One of the great hopes in dark matter indirect detection is that if cold dark matter is “simple” in some rigorous sense, and it has some internal physics, then there might be (self)annihilation of the dark matter.
This could show up as a gamma ray signature, somewhere up in the multi-GeV energy range:
cf.

simulation of possible γ-ray emission signature of annihilating CDM from
Article in Physics World

This depends on the dark matter having some finite cross-section for interaction, and a finite branching ration via Z0, or some such, to photon pair emission.

So, physics.

The simplest such physics have the γ-ray signal proportional to the density of the dark matter squared, so the spikes in dark matter density around the supermassive black holes can make a big difference in the prospect for detection. Many orders of magnitude stronger signals.

There is a lot of assumptions here, but it makes for fun and easy models to play with, which provide formal constraints on CDM mass, cross-sections and branching ratios, as detection limits get squeezed.
And, there could be actual detection for not-unreasonable simple CDM candidates…

So… what I have learned is:

1) CDM modelers do not generally have good perspective on which astronomical observations are robust to more than one signficant figure, if that.

2) CDM modelers like to take wildly optimistic scenarios for the astrophysical processes to optimize their estimates for likelihood of detection

3) If you do a lot of experiments looking for detections, including post hoc analysis of archival data, then you get a lot of 2.x σ signals.
Any one of which might be interesting individually, but are collectively clearly noise.

And

4) There is actually reasonably prospect for either indirect or direct detection of cold dark matter in the finite future, possibly within graduate student lifetimes, if nature is kind and CDM is relatively simple with no hidden nastinesses which forbid detection.

I now want to revisit some of the crazier ideas I had about CDM in years past which got blown away as too wild back when…

I still think the True Insight is hexapodia low surface density dwarf galaxies, but then I have always had a peculiar fondness for these.

PS: Fermi really is unreasonably good at what it does.
I am sooooooooooooooo jealous.

Comments

  1. #1 Alex Besogonov
    February 9, 2011

    Hexapodia? Should you be banned from the Relay?

  2. #2 tbird49er
    February 9, 2011

    Ya may have “been struck by several things”, but not measurable, definitive Dark Matter, apparently! hehehe lol

  3. #3 Steinn Sigurdsson
    February 9, 2011

    Well, I ought to have been struck by a lot of dark matter, unless it is more clumped then we think, but none of it stuck apparently.

    The Relay repairs itself and relays the messages. Even if they have to go round the long way. Word.

  4. #4 Dan Echegoyen
    February 9, 2011

    BLACK HOLES, EXPANSION, AND DARK ENERGY

    In the continuum of space and time, exists the dichotomy of matter and energy. All things exist as both matter and energy, but are experienced as one or the other.
    As energy, all things exist as wave patterns. Most wave patterns are interferences of simpler wave patterns. The simplest wave forms are those that do not interfere with other waves. These simplest wave forms hold their shape as they propagate. There are three such wave forms.
    The first such wave form is seen in three dimensions as the spherical expansion wave of a bomb blast, and in two dimensions as the circular wave of expansion on the water where a rock was tossed in. The second wave form is seen in three dimensions as the cone of sonic boom following an aircraft traveling faster than sound, and in two dimensions as the V-wake on the water where the boat is traveling faster than the water wave. The third wave form is seen in three dimensions as the propagation torus of a smoke ring and is seen in two dimensions as the double vortexes of an oar stroke on the water.
    The Torus is a particle of discrete exchange, from one point to another. The object exchanges position and momentum. While the spherical wave shows position, and the conic wave shows momentum, the torus shows both at the same time, and has a dynamic finite unbounded reality. The volumes of the cone, sphere, and torus are mathematically related as static objects.
    The Universe is a local density fluctuation. (a wave pulse) On this local density fluctuation wave, lesser wave forms may exist. All simple wave forms are also local density fluctuations, and as such are indeed universes in their own right, where other waves may exist.
    Consider the torus as a universe. Einstein said that gravity is indistinguishable from acceleration. There is both linear acceleration and angular acceleration. Although the torus as a whole travels in a straight line, every local point on the torus travels in a circle and experiences angular acceleration.
    The rubber sheet model of gravity and curved space translates directly to the propagating torus with angular acceleration. Acceleration is downward on the rubber sheet and outward on the torus. The tension field that separates the inside of the torus from the outside holds its shape as a simple two dimensional field of space and time just as the rubber sheet does.
    Experimentally verifiable is that a big fat slow smoke ring generated in a room with very still air will eventually possess a bulge that travels in a circle on the surface of the smoke ring. This bulge, being a gravitational depression, gathers more of the energy of the field toward itself. Finally the bulge gathers enough material to collapse the field and eject a new, smaller smoke ring out in the same direction as the first torus. This collapse is a black hole to the first torus, and a white hole to the second torus, where the axes of space and time in that second torus have reversed.
    While gravity tends to draw depressions together locally on a dynamic torus, even to the point of field collapse, other areas on a torus expand and contract globally as the torus propagates along without regard to local phenomenon on the surface. This is quintessence. The inertia of the torus to propagate is its dark energy. This is a two-dimensional example of the process that we experience in three dimensions.

    From structureofexistence.com by Dan Echegoyen 951-204-0201


    Dan Echegoyen
    author of StructureOfExistence.com
    (951) 204-0201

  5. #5 Andrew Shevchuk
    February 9, 2011

    This was a very convenient post. Thinking you might be in Aspen, I was just wondering yesterday if I should email you to inquire about any exciting news.

    Does anybody know if we’ll see XENON100 results at the particle physics conference next week? I admit to being an impatient grad student that has gained a new appreciation for those who have waited decades for these dark matter experiments.

  6. #6 Steinn Sigurdsson
    February 10, 2011

    Hm, McKinsey is talking here tomorrow, but I think that is the Xenon10 results and, I presume, LUX status.
    I don’t see any Xenon100 presentations scheduled, though there are some TBAs and I wouldn’t know all the X100 names.
    McKinsey is also presenting next week at the LHC conference on Xenon detectors.

    CDMS is also presenting tomorrow.

  7. #7 Alan
    February 10, 2011

    Way, way, way offtopic but while reading the article the black spot in the center of the graphic appears to pulsate and if I stare at either of the bottom corners of the graphic’s frame then the central black spot vanishes in my blind spot and the whole thing looks blue.

    The pulsating effect is the best accidental optical illusion I’ve seen in a long time, if you want to try and reproduce it you need to be at slightly less than arms length from the monitor in a dark room, as your eye moves from word to word in the text above the graphic it should start to pulsate.