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Dark Matter: Flashes Beneath the Earth

Dark matter is interesting in its own right, a mysterious ‘something’ that according to WMAP data must account for 23 percent of the universe (the breakdown now thought to be 72 percent dark energy, 23 percent dark matter, 4.6 percent atoms and less than 1 percent neutrinos). From a propulsion standpoint, dark matter intrigues us because it may represent a reaction mass conceivably useful for future space flight. It’s also Nobel Prize territory for the team that identifies it, which is why so many teams are looking, with one team’s provocative results drawing criticism.

The Italian and Chinese physicists on the DAMA Project have held out since 2000 for their claim that they are detecting dark matter beneath the Gran Sasso mountain in Italy. The modulation is yearly and could represent the Earth’s motion through a dark matter stream as it orbits the Sun. The larger DAMA/LIBRA experiment now reaffirms the phenomenon, which appears as flashes in the team’s sodium iodide detector. With the rate of flashes highest in June and lowest in December, the findings are provocative.

Such flashes could signal WIMPs (weakly interacting massive particles), which pass through most matter as if it were not there. But are the flashes DAMA/LIBRA is seeing enough to claim a detection of dark matter, or do they merely open up a range of possibilities? Cosmic Variance recently let Juan Collar (University of Chicago), himself a member of a dark matter team, loose on the question. Collar believes the modulation the team is finding is unmistakable, but disputes the team’s conclusions:

…to conclude from something this mundane that the experiment “confirms evidence of Dark Matter particles in the galactic halo with high confidence level” or that there is “an evidence for the presence of dark matter particles in the galactic halo at 8.2 sigma confidence level” is simply delusional. There is evidence for a modulation in the data at 8.2 sigma, stop. Compatible with what would be expected from some dark matter particles in some galactic halo models, full stop. Anything beyond this is wanting to believe, and it smears on the rest of us in the field. Of course, of course… there is no other observed process in nature that peaks in the summer and goes through a low in winter, so this must be dark matter, right? (Occam is turning in his grave, rusty razor still in hand. He is thinking a remake of that opening scene in “Un chien andalou”, with help from this little lady. I am channeling him loud and clear).

Collar is obviously a lively guy with eclectic tastes. I had to look up Un chien andalou, which turns out to be a surrealist film by Luis Buñuel and Salvador Dalí, one whose Wikipedia summation leaves me inclined to avoid it. He may be right about Occam, though. What about the possibility of experimental error in the DAMA/LIBRA experiments? Collar thinks we can’t rule it out, and is critical of the team’s attempts thus far to do so.

But this is not a slash and burn job on a particular experiment. Collar calls the work of DAMA/LIBRA ‘phenomenal’ on many fronts, and finds much to admire in it. But his appraisal is leavened with deep skepticism, and it’s one I wanted to call to your attention because of Collar’s high visibility in this area (he’s quoted in this New York Times article on the difficulty of dark matter detection) and because his lengthy post is a great example of what weblogs can do to spread good science from the source.

Centauri Dreams takes no position at all on DAMA/LIBRA other than to report the ongoing controversy, which all dark matter watchers will follow with interest. As I say, whoever does confirm a dark matter detection is easily in Nobel range. On that score, be aware as well of the Large Underground Xenon detector (LUX), which will look for evidence of dark matter in an abandoned South Dakota goldmine. Here we’re talking about 600 pounds of liquid xenon suspended in a huge water tank, some 4800 feet underground in the Homestake mine near Lead, South Dakota. The signature of dark matter would again be the flashes given off by WIMPs as they hit xenon atoms. Expect this experiment to start coming together later in the year as the mine is prepared to receive its equipment.

Comments on this entry are closed.

  • Athena April 26, 2008, 17:48

    Un Chien Andalou is a famous (notorious) film and, like all of Buñuel’s, it makes for uncomfortable watching.

    From Dr. Collar’s post, it’s clear that he’s on the MACHO, rather than the WIMP, side of the debate (*laughs*). Seriously, though, I detect a note of jealousy in his scorched-earth post — he is, after all, a direct competitor of the DAMA team. On the third hand, Ithe claims of the DAMA team do sound a bit grand, but independent observations should help reach a consensus.

  • James M. Essig April 26, 2008, 17:58

    Hi Paul;

    This is an outstanding article! Dark matter’s potential as a reaction mass definately might outdo baryonic matter since it would on average exist in 5.5 fold greater concentration within our universe. It occurred to me that some dark matter reactions might be more rest mass specific energetic than pure conversion of general relativistic baryonic mass into energy according to the famous relationship E = M(C EXP 2). If there existed any form of confinable dark matter with rest mass specific reaction energy of E = aM(C EXP 2) where a is much much greater than unity, perhaps we would have a fantastic reaction mass and otherwise energy supply with which to reach extraordinarilly high gamma factors with large manned interstellar space craft thus allowing humans from the current era of the cosmos to potentially travel into the cosmically distant future as a result of relativistic time dilation.

    Perhaps, as has been the subject of much speculation, there are multple forms of Cold Dark Matter. Since, baryonic matter makes up only 4.6 percent of the matter of the universe or about 1/5 the matter of the universe, one might speculate whether or not there are roughly 5 types of Cold Dark Matter. Perhaps there are even more types of Cold Dark Matter some of which have a reduced gravitational coupling to the space time and mass-energy within our universe. Accordingly, the amount of mass, for lack of a better word, might be greater than the amount that would exist if only purely general relativistic mass-gravity dynamics was at play here.

    Either way, even if the above speculations have no basis in reality, we can expect novel physics to be discovered with the systematic and theoretical study of dark matter and, at the least, we should have on average potentially 5.5 times the amount of reaction mass to use in interstellar space propulsion. I will be happy with any additional mattery supply that helps us, at the very least, attain ever highter gamma factors in sub C interstellar and God willing intergalactic travel. I think the fun is only just beginning.



  • Administrator April 26, 2008, 21:01

    Athena, right you are about Un Chien Andalou! Although a true old movie buff, I know very little about Buñuel. Interesting work at all the dark matter projects; I have the feeling we’re getting close, but reading Juan Collar’s thoughts really illuminated how tricky this investigation is.

  • James M. Essig April 26, 2008, 22:28

    Hi Folks;

    The possibility according the the Many World’s interpretation of quantum mechanics of the constant formation of huge if not infinite numbers of parallel histories wherein an entire branch or history forms for every act of quantum decoherence intreagues me as a way to perhaps generate all the more territory for humanity to inhabit and explore providing that there is some way to access and/or to artificially produce parallel histories with the right characteristics. I can imagine a whole ensemble of parallel Earths with highways running between them. Anyone for stopping at exit 123,456,789 along I-95!

    The idea that there may be multiple, perhaps even an ensemble of parallel universes that occupy some sort of overarching space time in which our universe is, for lack of a better word, embedded intregues me also. Perhaps any such parallel worlds might best be viewed as additional or alternate aspects or facets of what we know as baryonic matter, dark matter, and dark energy in a simmilar manner that a diamond cut and fashioned into a gem stone has many identical facets in terms of geometric facet shape and facet area. Perhaps there is much more than meets the eye in terms of the metaphorical diamond material that is located between the facets and for which the facets exist as accidental forms which subsist within the bulk base material we call diamond.

    As has been the subject of speculation, perhaps some of the effects we see as cold dark matter are in reality the effects of some nearby parallel universe(s) although the existence of weakly interacting matter might in reality effectively be such paralell universes in the sense that multiple cosmic structures would inhabit the same space-time. I often wonder, as is common in speculations about cold dark matter and socalled shadow matter whether whole CDM stars and planets might exist with ETI whose bodies are composed of CDM wherein all of the CDM would be natural as opposed to some effect that the ETI may have brought about by technological manipulation of matter and fields.



  • Adam April 27, 2008, 1:42

    Hi Jim

    I do wonder what the CMB will be like at high gamma-factors. If we push a gamma of 1,000 that means the CMB is blue-shifted into visible frequencies at 2735 K, and the sky is focussed to directly forward of the vehicle. The light pressure would be ~ 0.08 Newtons for every square metre facing forward. Increase the speed 10-fold and the force is ~ 800 N, a hundred fold and it’s 8 MPa. Those might seem like ludicrous gamma-factors, but the latter pressure is reached after just 97,000 light years at 1 gee. Intergalactic travel might only happen at low gamma-factors or only after the CMB has sufficiently declined to allow travel.

    Another curiosity is that to counteract the “CMB drag” at gamma 100,000 one’s engines would need to be blasting at the equivalent of 40 gees just to maintain speed, assuming a 1,000 ton ship with a 50 sq.m cross-section. Absorbing and re-emitting it rearwards would reduce that, but I’ve no idea what could interact with such a photon barrage and remain coherent matter. Perhaps very tricky x-ray light-pipes?

  • Ron S April 27, 2008, 10:05

    I was recently reading about experiments and theories surrounding high-gamma factor particles with the CMB – specifically, cosmic rays interacting with CMB photons. Considering Jim’s and Adam’s comments perhaps there is some interest here on this.


    There is a predicted limit to cosmic ray energy from extra-galactic sources due to these interactions. There are some theorists trying to tie this threshold to quantum gravity theories.

  • James M. Essig April 27, 2008, 10:44

    Hi Adam;

    Thanks for the insight and comments on drag verses high gamma factor.

    Perhaps one way to deal with drag at visible light to x ray frequencies would be to include so-called negative refraction index materials in the front of the ship that are greatly heat and radiation tolerant. Materials with a negative refraction index are now under investigation by a number of institutions including the U.S. Department of Defense and Duke University of Chapel Hill North Carolina. Negative index of refraction materials have the unusual property of being pulled in the direction of incident light rather than being pushed

    The caveat here would be to produce negative refraction index materials that would be operative over a wide range of energetic frequences. Negative refractive index materials as they are currently being researched are so-called meta-materials that get their overall global properties from the combined effect of aggregated microscopic or nanoscale structures. For the negative index of refraction materials being studied, I believe the tiny structures are electrically conducting loops or coil like arrangements.

    Obviously, to handle the light influx associated with 40 Gs would require one heck of a rapid heat dump which might be provided in part by some turboelectric system to power an ion, electron, or photon rocket or some other mechanism.

    Perhaps somehow, negative index of refraction materials can oneday be made of solid nuetronium, quarkonium, or simmilar material that is capable of negatively refracting hard gamma rays. The other option might be to build huge accelleration tubes wherein the outerwalls of the tubes would be composed of CMBR reflecting superconducting materials wherein a thermal gradient would be set up between the inside of the tubes and the outside to reduce black-body emmissions inside the tube.

    Another option would be to include a very very elongated cone-like structure in front of the craft such that the incomming photons would be scattered at an angle off the cone thus effectively reducing their momentum transfer to the ship. The cone could be elongated as the ship increased its gamma factor to account for Lorenz contraction.



  • dad2059 April 28, 2008, 7:08

    This is pretty exotic physics for me to grok so forgive me for asking dumb questions about this topic, but here goes.

    Is dark matter the same as ‘negative matter’? It has been posited that negative matter is needed to keep wormhole mouths open (if they exist). So couldn’t dark matter , if it can be manipulated, be used as scaffolding to hold wormholes open?

    Yeah, I know it’s FTL wishful thinking, but I had to give it a shot!

  • Administrator April 28, 2008, 7:44

    Not a dumb question at all, dad2059, and believe me, this stuff is exotic for all of us. In the context of wormholes, let’s start with negative energy rather than negative matter. Negative energy is thought necessary to keep a wormhole’s mouth open. Needless to say, it’s quite tricky, and we have no idea how to manipulate it other than to study it at the smallest levels, as in the Casimir effect. Negative matter has never actually been observed, but if it exists, it’s exotic indeed, different from antimatter in that it would not fall in a gravitational field but move away. It would be repelled by normal matter, and would thus be hard to locate, if indeed it does exist. It could have interesting ramifications in terms of wormholes as well.

    Dark matter, at least as we understand it thus far, wouldn’t help with a wormhole — it’s doesn’t seem to act like negative matter. But if we can somehow learn to work with negative energy (and perhaps negative matter, assuming we do find it somewhere) in the future, perhaps in the presence of large gravitational fields, we may be able to do some interesting things! Others here know much more about negative matter and energy, so you’ll doubtless be getting better responses than mine, either here or via e-mail.

  • david lewis April 28, 2008, 8:52

    If dark matter exists and is so much more common than normal matter then I wonder how that would affect a craft moving at high speeds. Would the result of a vessel moving at 10 percent light speed colliding with dark matter be the same as such a vessel hitting normal matter? Would dark matter be distributed between the stars in much the same way as normal matter – a few atoms per cubic centimeter, with some clustered in in comets and wandering planets.

    Those might seem like ludicrous gamma-factors, but the latter pressure is reached after just 97,000 light years at 1 gee.

    Wow. So a craft trying to cross the intergalactic gulf would not be able to accelerate continuously to the half way point. At least not without some serious improvements in our materials science.

  • Ron S April 28, 2008, 10:37

    There’s lots of material out there about negative matter etc., so I’ll suggest this reference to an overview. It’s concise and seems to be correct.


  • Administrator April 28, 2008, 12:21

    david, dark matter as we currently view it seems unlikely to pose a problem to a fast moving craft, at least if we follow the WIMP (weakly interacting massive particle) paradigm. These are thought to be so exquisitely hard to detect because they pass through normal matter as if it weren’t there. Obviously, any true conclusions on this await a deepening of our understanding of what dark matter is, something these various projects should eventually help us with.

  • Hans Bausewein April 28, 2008, 14:56

    A detector on another solar system body would also help a lot. Then it would become sure (or falsified) that the periodic change is caused by movement through the interstellar medium and not by something local to earth.

  • James M. Essig April 28, 2008, 16:58

    Hi Folks;

    This thread is turning out to be popular. Very interesting topic indeed.

    I was reading a textbook in sub-atomic physics early this morning when I stumbled accross a brief statement about the proposed Rare Isotope Collider or RIC which will collide rare isotopes, presumably including with those of very high atomic number and atomic mass in an attempt to produce yet to be discovered isotopes and elements.

    Such a machine can only help us understand the strong nuclear force and the interaction of gluons and qaurks under the process of quantum-chromo-dynamics or QCD and, who knows, perhaps shed light on any other aspects of sub-atomic structure, perhaps even finding evidence of additional nuclear forces, one or more of which just might be stronger than the strong nuclear force.

    With the resumption of the activities of the upgraded CERN facility of the LHC, the proposed upgrade of the Relativistic Heavy Ion Collider, and the RIC, and other proposed machines, I think we are bound to discover new particles, perhaps those predicted by super-symmetry as candidates for Cold Dark Matter.

    I think particle physics is going to get real interesting again very soon.



  • James M. Essig May 1, 2008, 0:09

    Hi Folks;

    We are all well familiar with the composite nature of matter such as the molecular composition of our bodies, the atomic composition of our molecules, and the nucleonic and electronic composition of atoms and the sub-composition of quarks and gluons. We are even familiar with concepts such as the fine grained discreetization of space time from quantum field theories all the way to modern loop quantum gravity, holographic information theory, etc..

    Now what if there existed a material that was completely continuous, absolutely continuous with no sub-structure, in fact no substructure other than regions defined by differential distance, area, or volumetric elements as purely a mathematical concern. Moreover, one could imagine such materials as extending into, or having any of the shapes which could be definable in terms of, abstract mathematical space.

    One wonders if there could be any aspect of creation, anyform of universe or multiverse, or any aspect of the cosmos from either the physical or spiritual stand point where such materials might exist. I wonder if there could be ETI beings or somehow purely spiritual beings that are discarnate but wherein these purely spiritual beings would percieve themselves as having shape or size in the purely imaginative sense. Perhaps such beings would not perceive themselves as having any shape, size, or extention but rather as having bodies that are made out of pure emotional qualities or of pure abstract conscious thought of abstact concept elemental form.

    I bring these concepts up not to try to impress anyone nor to try to promote spiritualism, but rather as a legitament object of enquiry as we all contemplate this vaste realm we know as the cosmos, or creation, for lack of a better word. But for now, I will settle with just finding some WIMPS or other dark matter candidates when the LHC goes on line.



  • ljk May 1, 2008, 10:30

    Charge amplification concepts for direction-sensitive dark matter detectors

    Authors: D.Dujmic, P.Fisher, G.Sciolla, S.Ahlen, V.Dutta, S.Henderson, A.Kaboth, G.Kohse, R.Lanza, J.Monroe, A.Roccaro, N.Skvorodnev, H.Tomita, R.Vanderspek, H.Wellenstein, R.Yamamoto

    (Submitted on 30 Apr 2008)

    Abstract: Direction measurement of weakly interacting massive particles in time-projection chambers can provide definite evidence of their existence and help to determine their properties.

    This article demonstrates several concepts for charge amplification in time-projection chambers that can be used in direction-sensitive dark matter search experiments.

    We demonstrate reconstruction of the ‘head-tail’ effect for nuclear recoils above 100keV, and discuss the detector performance in the context of dark matter detection and scaling to large detector volumes.

    Comments: 15 pages, 9 figures

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0804.4827v1 [astro-ph]

    Submission history

    From: Denis Dujmic [view email]

    [v1] Wed, 30 Apr 2008 13:54:51 GMT (2305kb,D)


  • James M. Essig May 1, 2008, 20:07

    Hi Folks;

    It would be interesting if we could alter the zero point virtual fields in such a manner that a preponderance of net electrically charged virtual particle matter would exist such that an electrodynamic propulsion system could use the net virtual charge as a reaction mass or as a virtual reaction mass. I could well imagine that the strength of the repulsive and/or attactive electric fields generated by a ship using the virtual fields as a reaction mass would need to be extraordinarilly high to manifest rapid accelleration or for even accelleration on the order of 1 G.

    If the net virtual charge patterns could be set up so that a virtual electric field gradient would extend orthogonally into higher dimensional space from any or all of the three dimensional axes of space in which the ship is located, perhaps the ship could be pulled into the higher dimensional space, or for lack of a better word, hyperspace.

    One can imagine that higher dimensional travel including space time shortcuts into remote spatial-temporal locations within our universe, other universes, paralell universes, etc., might be facilitated by such exotic technology.

    The caveat to using such biased zero point fields is: 1) How to produce them and 2): How to make their interaction with the ships field strong enough for useful repulsion. I hold out some hope that we can learn how to react against the zero point fields by the fact that we can detect the force set up in Casimar experimental setups which results from an embalance within reflected zero point electromagnetic fluctuations.

    I will have more to say on this and related concepts in the days ahead.



  • David Wall May 3, 2008, 12:07

    How can dark matter be useful as reaction mass if it
    interacts with us only gravitationally? Wouldn’t a
    chemical or nuclear explosion just pass right through

  • Administrator May 3, 2008, 12:47

    It’s a good question, David, and the answer is that we just don’t know enough about dark matter to be sure if it has potential uses in propulsion. It may well not, but let’s keep the possibility open as we explore its characteristics. You’re right, I think, that from where we stand now, the idea seems unlikely.

  • James M. Essig May 3, 2008, 20:05

    Hi Folks;

    One can imagine using any of what is appearing to become a wide variety of fields to use as repulsive and/or attractive media for interstellar propuslion.

    If the virtual zero point mass of the zero point massive particles could somehow be enhanced, then we might have an excellent medium with which to react against with say an artificially produced gravity field or antigravity field, perhaps produced electrogravatically. I won’t comment much about this concept because the open literature is repleat which theories of gravatic field effect propulsion schemes, some of which most probably merit good investigation.

    I thought that I would comment about using real and/or virtual zero point vacuum field dark matter particles and fields for propulsion. Just as we have the electrically charged particles such as the charged leptons and the quarks and the electromagnetic photon, we also may have the selectrons and squarks and the photino. We may have gravitinoes, gluinos, and the weak force supersymmetric analogue particles to work with as well.

    My thinking is that if we can set up fields involving the reaction between squarks, sleptons, and the photino, we might have the supersymmetric analogue of electrodynamic propulsion. If we can bias the zero point virtual fields and use them as supersymmetic based reaction masses or for field effect propulsion that would be good also.

    The use of the LHC to try to find supersymmetric particles I hope will yield some real interesting results. The more we learn, the better we will be equiped to study how to apply related fields for any useful interstellar travel purposes.



  • george scaglione May 4, 2008, 11:05

    jim as david says above wouldn’t it be kind of hard to use dark matter,that is “harness” dark matter for any purpose of ours!? heck,we don’t even really know yet what the stuff is!now…having said that…good ideas!!! those aliens we like to speak of who are a million years advanced in science on us had to start someplace too. and i have a feeling that it was,would have been,something just like this! thank you your friend george ps paul agree with your comments also! but i hope for the best.we never really know what it is that we might learn! ;) g

  • ljk May 4, 2008, 23:36

    Mirror dark matter and the new DAMA/LIBRA results: A simple explanation for a beautiful experiment

    Authors: R. Foot

    (Submitted on 29 Apr 2008)

    Abstract: Recently, the DAMA/LIBRA experiment has convincingly confirmed the DAMA/NaI annual modulation signal, experimentally demonstrating the existence of non-baryonic dark matter in the halo of our galaxy. Meanwhile, in another part of town, other (higher threshold) experiments such as CDMS and XENON10 have not detected any evidence for dark matter.

    One promising dark matter candidate which can reconcile the positive DAMA annual modulation signal with the null results from the other experiments, is mirror dark matter. We re-analyse the mirror matter interpretation of the DAMA annual modulation signal utilizing a) the new data from DAMA/LIBRA, including the measured energy dependence of the annual modulation signal b) an updated quenching factor which takes into account the channeling effect in $NaI$ crystals and c) the latest constraints from CDMS/Ge, CDMS/Si and XENON10 experiments.

    We show that the simplest possibility of a $He’$ (and/or $H’$) dominated halo with a small $O’$ component is sufficient to fully explain all of the dark matter experiments. We also point out that a certain class of hidden sector dark matter models, although theoretically less appealing and less constrained, can mimic the success of the mirror dark matter model and hence are also viable.

    Comments: about 20 pages, 6 figures

    Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph)

    Cite as: arXiv:0804.4518v1 [hep-ph]

    Submission history

    From: Robert Foot [view email]

    [v1] Tue, 29 Apr 2008 06:27:18 GMT (29kb)


  • ljk May 5, 2008, 22:55

    A New Channel for Detecting Dark Matter Substructure in Galaxies: Gravitational Lens Time Delays

    Authors: Charles R. Keeton (Rutgers), Leonidas A. Moustakas (JPL/Caltech)

    (Submitted on 2 May 2008)

    Abstract: We show that dark matter substructure in galaxy-scale halos perturbs the time delays between images in strong gravitational lens systems. The variance of the effect depends on the subhalo mass function, scaling as the product of the substructure mass fraction and a characteristic mass of subhalos (namely /). Time delay perturbations therefore complement gravitational lens flux ratio anomalies and astrometric perturbations by measuring a different moment of the subhalo mass function.

    Unlike flux ratio anomalies, “time delay millilensing” is unaffected by dust extinction or stellar microlensing in the lens galaxy. Furthermore, we show that time delay ratios are immune to the radial profile degeneracy that usually plagues lens modeling. We lay out a mathematical theory of time delay perturbations and find it to be tractable and attractive.

    We predict that in “cusp” lenses with close triplets of images, substructure may change the arrival-time order of the images (compared with smooth models). We discuss the possibility that this effect has already been observed in RX J1131-1231.

    Comments: version 2 submitted to ApJ

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.0309v1 [astro-ph]

    Submission history

    From: C. R. Keeton [view email]

    [v1] Fri, 2 May 2008 20:01:59 GMT (290kb)


  • ljk May 7, 2008, 8:47

    Direct dark matter identification with a hybrid detection technique

    Authors: A Bueno, M C Carmona, A J Melgarejo

    (Submitted on 6 May 2008)

    Abstract: In the quest to understand the ultimate nature of WIMPs, we propose the use of a hybrid detection technique: cylinders filled with liquefied noble gasses, acting as targets, are immersed inside a tank of Gd-doped ultra-pure water that provides an active and efficient veto against neutrons.

    The evaluation of the background rejection capabilities and physics potential of this instrument have been carried out through a full GEANT4 simulation, assuming the detector will be located at the Canfranc underground laboratory (in the Spanish Pyrenees). Our results compare very favourably with existing or planned experiments in the field. This technique is scalable and will allow to reach target masses of few tonnes in the next future.

    Comments: 15 pages, 5 figures

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.0694v1 [astro-ph]

    Submission history

    From: Antonio Bueno [view email]

    [v1] Tue, 6 May 2008 16:14:14 GMT (100kb)


  • ljk May 7, 2008, 8:49

    WMAP5 constraints on the unified model of dark energy and dark matter

    Authors: T. Barreiro, O. Bertolami, P. Torres

    (Submitted on 6 May 2008)

    Abstract: We derive constraints on the parameter space of the unified model of dark energy and dark matter, the Generalized Chaplygin Gas (GCG), from the amplitudes and positions of the first few peaks and first trough of the cosmic microwave background radiation (CMBR) power spectrum, using the latest WMAP five year data.

    Comments: 5 pages, 6 figures

    Subjects: Astrophysics (astro-ph)

    Report number: DF/IST-3.2006

    Cite as: arXiv:0805.0731v1 [astro-ph]

    Submission history

    From: Tiago Barreiro [view email]

    [v1] Tue, 6 May 2008 14:23:09 GMT (707kb)


  • ljk May 21, 2008, 11:27

    Limits on spin-dependent WIMP-nucleon cross-sections from the XENON10 experiment

    Authors: J. Angle, E. Aprile, F. Arneodo, L. Baudis, A. Bernstein, A. Bolozdynya, P. Brusov, L.C.C. Coelho, C.E. Dahl, L. DeViveiros, A.D. Ferella, L.M.P. Fernandes, S. Fiorucci, R.J. Gaitskell, K.L. Giboni, R. Gomez, R. Hasty, L. Kastens, J. Kwong, J.A.M. Lopes, N. Madden, A. Manalaysay, A. Manzur, D.N. McKinsey, M.E. Monzani, K. Ni, U. Oberlack, J. Orboeck, G. Plante, R. Santorelli, J.M.F. dos Santos, P. Shagin, T. Shutt, P. Sorensen, S. Schulte, C. Winant, M. Yamashita, for the XENON10 Collaboration

    (Submitted on 19 May 2008)

    Abstract: XENON10 is an experiment to directly detect weakly interacting massive particle (WIMPs), which may comprise the bulk of the non-baryonic dark matter in our Universe. We report new results for spin-dependent WIMP-nucleon interactions with 129-Xe and 131-Xe from 58.6 live-days of operation at the Laboratori Nazionali del Gran Sasso (LNGS).

    Based on the non-observation of a WIMP signal in 5.4 kg of fiducial liquid xenon mass, we exclude previously unexplored regions in the theoretically allowed parameter space for neutralinos. We also exclude a heavy Majorana neutrino with a mass in the range of 10 GeV -2 TeV as a dark matter candidate under standard assumptions for its density and distribution in the galactic halo.

    Comments: 4 pages, 4 figures; submitted to PRL

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.2939v1 [astro-ph]

    Submission history

    From: Laura Baudis [view email]

    [v1] Mon, 19 May 2008 20:32:58 GMT (38kb)


  • ljk May 22, 2008, 21:29

    Testing for no dark matter

    You might recall a while back we reported on a prediction for peculiar event
    that takes place on the two equinoxes…


  • ljk May 27, 2008, 11:48

    Dark Matter Densities during the Formation of the First Stars and in Dark Stars

    Authors: Katherine Freese, Paolo Gondolo, J. A. Sellwood, Douglas Spolyar

    (Submitted on 22 May 2008)

    Abstract: The first stars in the universe form inside $\sim 10^6 M_\odot$ dark matter (DM) haloes whose initial density profiles are laid down by gravitational collapse in hierarchical structure formation scenarios. During the formation of the first stars in the universe, the baryonic infall compresses the dark matter further.

    The resultant dark matter density is presented here, using an algorithm originally developed by Young to calculate changes to the profile as the result of adiabatic infall in a spherical halo model; the Young prescription takes into account the non-circular motions of halo particles. The density profiles obtained in this way are found to be within a factor of two of those obtained using the simple adiabatic contraction prescription of Blumenthal et al.

    Our results hold regardless of the nature of the dark matter or its interactions and rely merely on gravity. If the dark matter consists of weakly interacting massive particles, which are their own antiparticles, their densities are high enough that their annihilation in the first protostars can indeed provide an important heat source and prevent the collapse all the way to fusion. In short, a “Dark Star” phase of stellar evolution, powered by DM annihilation, may indeed describe the first stars in the universe.

    Comments: 14 pages, 3 figures, and 1 table

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.3540v1 [astro-ph]

    Submission history

    From: Douglas Spolyar [view email]

    [v1] Thu, 22 May 2008 21:10:45 GMT (139kb)


  • ljk May 29, 2008, 12:53

    Dark matter annihilation effects on the first stars

    Authors: F. Iocco, A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara, P. Marigo

    (Submitted on 26 May 2008)

    Abstract: We study the effects of WIMP dark matter (DM) on the collapse and evolution of the first stars in the Universe. Using a stellar evolution code, we follow the pre-Main Sequence (MS) phase of a grid of metal-free stars with masses in the range 5-600 solar mass forming in the centre of a 1e6 solar mass halo at redhisft z=20.

    DM particles of the parent halo are accreted in the proto-stellar interior by adiabatic contraction and scattering/capture processes, reaching central densities of order 1e12 GeV/cm3 at radii of the order of the AU: energy release from annihilation reactions can effectively counteract the gravitational collapse. This induces a transient stalling phase (i.e. a “dark” star) lasting from 2.1e3 yr (M=600 solar mass) to 1.8e4 yr (M=9 solar mass). Later in the evolution, DM scattering/capture rate becomes high enough that energy deposition from annihilations significantly alters the pre-MS evolution of the star in a way that depends on DM (i) velocity dispersion, (ii) density, (iii) elastic scattering cross section with baryons.

    For our fiducial set of parameters (10 km/s, 1e11 GeV/cm3, 1e-38 cm2) we find that the evolution of stars of mass lower than 40 solar masses “freezes” on the HR diagram before reaching the ZAMS. Stars with bigger masses manage to ignite nuclear reactions; however, DM “burning” prolonges their lifetimes by a factor 2 (5) for a 600 (40) solar mass star.

    Comments: Comments welcome

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0805.4016v1 [astro-ph]

    Submission history

    From: Fabio Iocco [view email]

    [v1] Mon, 26 May 2008 20:06:09 GMT (147kb)


  • ljk June 3, 2008, 23:41

    Dark matter and the LHC

    Authors: Howard Baer, Xerxes Tata

    (Submitted on 13 May 2008 (v1), last revised 29 May 2008 (this version, v2))

    Abstract: An abundance of astrophysical evidence indicates that the bulk of matter in the universe is made up of massive, electrically neutral particles that form the dark matter (DM). While the density of DM has been precisely measured, the identity of the DM particle (or particles) is a complete mystery. In fact, within the laws of physics as we know them (the Standard Model, or SM), none of the particles have the right properties to make up DM.

    Remarkably, many new physics extensions of the SM — designed to address theoretical issues with the electroweak symmetry breaking sector — require the introduction of new particles, some of which are excellent DM candidates. As the LHC era begins, there are high hopes that DM particles, along with their associated new matter states, will be produced in pp collisions.

    We discuss how LHC experiments, along with other DM searches, may serve to determine the identity of DM particles and elucidate the associated physics. Most of our discussion centers around theories with weak-scale supersymmetry, and allows for several different DM candidate particles.

    Comments: 25 two-column pages with 11 EPS figures. Invited book chapter for volume on LHC physics to celebrate the Platinum Jubilee of the Indian National Science Academy, edited by Amitava Datta, Biswarup Mukhopadhyaya and Amitava Raychaudhuri. Latex file needs style file insa.sty

    Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics – Experiment (hep-ex)

    Cite as: arXiv:0805.1905v2 [hep-ph]

    Submission history

    From: Howard Baer [view email]

    [v1] Tue, 13 May 2008 18:52:41 GMT (685kb)

    [v2] Thu, 29 May 2008 17:48:40 GMT (586kb)


  • ljk June 11, 2008, 23:14

    Two components of dark matter in the DAMA data

    Authors: Yukio Tomozawa

    (Submitted on 9 Jun 2008)

    Abstract: It is shown that the DAMA data indicate two dark matter components, one that circulates around the galactic center (GC) and another that is emitted from the GC. From the location of the maximum yearly variation, one can compute the ratio of the two components.

    Comments: 4 pages, no figure

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.1501v1 [astro-ph]

    Submission history

    From: Yukio Tomozawa [view email]

    [v1] Mon, 9 Jun 2008 17:28:38 GMT (6kb)


  • ljk June 17, 2008, 17:19

    Sun might hold secret of dark matter – USA Today


    By Jeanna Bryner, SPACE.com

    June 17, 2008

    The identity of the mysterious dark matter thought to
    pervade the universe has eluded astrophysicists for decades.
    Now, for the first time a team hopes to look inside the sun for
    one of the prime candidates….

    Two hypothetical particles have become the prime suspects
    to explain the fundamental make-up of dark matter: so-called
    axions and WIMPs (Weakly Interacting Massive Particles).

    Tens of teams are on the hunt for the heavyweight WIMPs,
    such as the GLAST team, which hopes to detect the gamma rays
    produced when, hypothetically, WIMPs and their antimatter
    selves annihilate each other….

    A team led by X-ray ASTRONOMER HUGH HUDSON OF UC
    BERKELEY says, however, that they are onto a promising and
    new way to search for the axion: Looking inside the sun.

    Hudson presented his research at a recent meeting of the
    American Astronomical Society (AAS) in St. Louis….

    For Hudson, solar axions hold another prize, a window inside
    the sun.

    “It would be revolutionary for solar and stellar physics to be
    able to make use of the axions, if real, to see inside the sun,”
    Hudson said, “and also to study the coronal magnetic field via
    the conversion process [of axions to photons].”

    Axions could help astrophysicists to make more accurate
    measurements of the temperature of the sun’s core, for instance.

  • ljk June 24, 2008, 11:13

    The EDELWEISS-II experiment

    Authors: S. Scorza (IPNL)

    (Submitted on 19 Jun 2008)

    Abstract: EDELWEISS is a direct dark matter search situated in the low radioactivity environment of the Modane Underground Laboratory. The experiment uses Ge detectors at very low temperature in order to identify eventual rare nuclear recoils induced by elastic scattering of WIMPs from our Galactic halo. The commissioning of the second phase of the experiment, involving more than 7 kg of Ge, has been completed in 2007. Two new type of detectors with active rejection of events due to surface contamination have demonstrated the performances required to achieve the physics goal of the present phase.

    Comments: 43rd Rencontres de Moriond – Electroweak Interactions and Unified Theories, La Thuile : Italie (2008)

    Subjects: Astrophysics (astro-ph); Instrumentation and Detectors (physics.ins-det)

    Report number: LYCEN 2008-08

    Cite as: arXiv:0806.3147v1 [astro-ph]

    Submission history

    From: Sylvie Flores [view email] [via CCSD proxy]

    [v1] Thu, 19 Jun 2008 07:49:21 GMT (766kb)


  • ljk June 26, 2008, 16:50

    Dark Matter in the Solar System

    Authors: X. Xu, E. R. Siegel

    (Submitted on 23 Jun 2008)

    Abstract: We determine the density and mass distribution of dark matter within our Solar System. We explore the three-body interactions between dark matter particles, the Sun, and the planets to compute the amount of dark matter gravitationally captured over the lifetime of the Solar System. We provide an analytical framework for performing these calculations and detail our numerical simulations accordingly.

    We find that the local density of dark matter is enhanced by between three and five orders of magnitude over the background halo density, dependent on the radial distance from the Sun. This has profound implications for terrestrial direct dark matter detection searches.

    We also discuss our results in the context of gravitational signatures, including existing constraints, and find that dark matter captured in this fashion is not responsible for the Pioneer anomaly.

    We conclude that dark matter appears to, overall, play a much more important role in our Solar System than previously thought.

    Comments: 7 pages, 3 figures, submitted to PRD

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.3767v1 [astro-ph]

    Submission history

    From: Ethan Siegel [view email]

    [v1] Mon, 23 Jun 2008 20:43:37 GMT (165kb)


  • ljk July 1, 2008, 12:49

    DAMA and WIMP dark matter

    Authors: Frank Petriello, Kathryn M. Zurek

    (Submitted on 25 Jun 2008)

    Abstract: We study whether spin-independent scattering of weakly-interacting massive particles (WIMPs) with nuclei can account for the annual modulation signal reported by DAMA. We consider both elastic and inelastic scattering processes.

    We find that there is a region of WIMP parameter space which can simultaneously accommodate DAMA and the null results of CDMS, CRESST, and XENON. This region corresponds to an ordinary, elastically-scattering WIMP with a standard Maxwell-Boltzmann distribution, a mass 3 GeV < m_{DM} <8 GeV, and a spin-independent cross section with nucleons 3 \times 10^{-41} cm^2 < \sigma_p^{SI} < 5 \times 10^{-39} cm^2.

    This new region of parameter space depends crucially on the recently discovered effect of channeling on the energy threshold for WIMP detection in the DAMA experiment; without the inclusion of this effect, the DAMA allowed region is essentially closed by null experiments. Such low-mass WIMPs arise in many theories of Beyond the Standard Model physics, from minimal extensions of the MSSM to solutions of the baryon-dark matter coincidence problem.

    We find that inelastic scattering channels do not open up a significant parameter region consistent with all experimental results. Future experiments with low energy thresholds for detecting nuclear recoils, such as CDMSII-Si and those utilizing ultra-low energy germanium detectors, will be able to probe the DAMA region of parameter space.

    Comments: 19 pages, 10 figures

    Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics – Experiment (hep-ex)

    Cite as: arXiv:0806.3989v1 [hep-ph]

    Submission history

    From: Frank J. Petriello [view email]

    [v1] Wed, 25 Jun 2008 19:47:44 GMT (176kb)


  • ljk July 1, 2008, 13:35

    Interpreting the recent results on direct search for dark matter particles in terms of relic neutralino

    Authors: A. Bottino, F. Donato, N. Fornengo (Torino U. & INFN, Turin), S. Scopel (KIAS, Seul)

    (Submitted on 25 Jun 2008)

    Abstract: The most recent results from direct searches for dark matter particles in the galactic halo are examined in terms of an effective Minimal Supersymmetric extension of the Standard Model at the electroweak scale without gaugino masses unification. We show that the annual modulation effect at 8.2 $\sigma$ C.L. recently presented by the DAMA Collaboration, as the result of a combined analysis of the DAMA/NaI and the DAMA/LIBRA experiments for a total exposure of 0.82 ton yr, fits remarkably well with what expected for relic neutralinos for a wide variety of WIMP distribution functions. Bounds derivable from other measurements of direct searches for dark matter particles are analyzed.

    We stress the role played by the uncertainties affecting the neutralino–quark couplings arising from the involved hadronic quantities. We also examine how present data on cosmic antiprotons can help in constraining the neutralino configurations selected by the DAMA effect, in connection with the values of the astrophysical parameters.

    Perspectives for measurement of antideuterons possibly produced in the galactic halo by self–annihilation of neutralinos belonging to the DAMA configurations are examined. Finally, we discuss how findings at LHC would impact on these issues.

    Comments: 18 pages, 10 figures

    Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph)

    Cite as: arXiv:0806.4099v1 [hep-ph]

    Submission history

    From: Fiorenza Donato [view email]

    [v1] Wed, 25 Jun 2008 14:01:27 GMT (380kb)


  • ljk August 6, 2008, 23:50

    Placing direct limits on the mass of earth-bound dark matter

    Authors: Stephen L. Adler

    (Submitted on 6 Aug 2008)

    Abstract: We point out that by comparing the total mass (in gravitational units) of the earth-moon system, as determined by lunar laser ranging, with the sum of the lunar mass as independently determined by its gravitational action on satellites or asteroids, and the earth mass, as determined by the LAGEOS geodetic survey satellite, one can get a direct measure of the mass of earth-bound dark matter lying between the radius of the moon’s orbit and the geodetic satellite orbit. Current data show that the mass of such earth-bound dark matter must be less than $4 \times 10^{-9}$ of the earth’s mass.

    Comments: Latex, 5 pages

    Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics – Phenomenology (hep-ph); Space Physics (physics.space-ph)

    Cite as: arXiv:0808.0899v1 [astro-ph]

    Submission history

    From: Stephen Adler [view email]

    [v1] Wed, 6 Aug 2008 18:34:47 GMT (5kb)


  • ljk August 6, 2008, 23:51

    Using the Energy Spectrum at DAMA/LIBRA to Probe Light Dark Matter

    Authors: Spencer Chang, Aaron Pierce, Neal Weiner

    (Submitted on 1 Aug 2008)

    Abstract: A weakly interacting massive particle (WIMP) weighing only a few GeV has been invoked as an explanation for the signal from the DAMA/LIBRA experiment. We show that the data from DAMA/LIBRA are now powerful enough to strongly constrain the properties of any putative WIMP.

    Accounting for the detailed recoil spectrum, a light WIMP with a Maxwellian velocity distribution and a spin-independent (SI) interaction cannot account for the data. Even neglecting the spectrum, much of the parameter space is excluded by limits from the DAMA unmodulated signal at low energies. Significant modifications to the astrophysics or particle physics can open light mass windows.

    Comments: 5 pages, 5 figures

    Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics – Experiment (hep-ex)

    Report number: MCTP-08-5

    Cite as: arXiv:0808.0196v1 [hep-ph]

    Submission history

    From: Spencer Chang [view email]

    [v1] Fri, 1 Aug 2008 22:39:24 GMT (1372kb,D)


  • ljk August 21, 2008, 22:22

    In the dark about dark matter

    Has a European satellite detected dark matter?