The cusp in the dark matter distribution required to explain the recently found excess in the gamma-ray spectrum at energies of 130 GeV in terms of the dark matter annihilations cannot survive the tidal forces if it is offset by 1.5° from the Galactic center as suggested by observations.From Dmitry Gorbunov, Peter Tinjakov, "On the offset of a DM Cusp and the interpretation of the 130 GeV line as a DM signal" via Tommasso Dorigo's blog.
One of the strongest bits of experimental data favoring WIMP (weakly interacting massive particle) dark matter with particle masses at the electroweak scale is the Fermi line, i.e. 130 GeV photon signals detected by the Fermi Gamma-Ray Space Telescope that have no understood astronomical process as its source.
These signals have been hypothesized by theorists to be evidence of the annihilation of matter and antimatter dark matter particles of about 130 GeV mass with each other. But, even if these signals are evidence of such annihilations, they can only be the dark matter that everyone is looking for as the biggest gap in fundamental physics today if the signals come mostly from the right direction. The latest study indicates that they do not. Thus, the Fermi line grows an ever lengthening list of possible direct detections of dark matter or dark matter annihilation signals that have been ruled out as true dark matter signals.
The Fermi line could still be real; it just can't be dark matter
The study still doesn't tell us if the Fermi line is "real" or just some sort of statistical or systematic error in the observations. So far, no plausible explanation that could explain the Fermi line as an experimental error has been identified.
But, for example, suppose there was a supersymmetric particle with that mass or a second kind of Higgs boson of slightly different mass than the one already discovered, that was highly unstable. If this particle existed, its annihilation could produce this signal in some unknown process, such as some kind of high energy interactions near the Milky Way's central black hole's event horizon, even though such an unstable particle can't be an important source of the phenomena attributed to dark matter.
A true SUSY optimist could see both the Fermi line and the ASM-02 positron excess as signatures of SUSY particle annihilations. But, even for a SUSY optimist, the likelihood that a canonical sparticle or SUSY Higgs boson can provide a dark matter candidate that fits the experimental evidence is rapidly waning.
The best hope in a SUSY theory for a dark matter candidate is now the same as it is in minimal Standard Model extensions - some sort of sterile (i.e. right handed) neutrino with a mass on the other of 2 keV (i.e. warm dark matter). These models are highly constrained and it hasn't been fully established that they can really reproduce all observed dark matter phenomena. But, these particles are the only game in town using the dark matter particle paradigm that hasn't been pretty definitively ruled out by observational evidence to date.
Independent lines of experimental evidence disfavor WIMP dark matter
This isn't too surprising.
Multiple lines of evidence disfavor weakly interacting dark matter particles with masses of 10 GeV or so or more. For example, heavy WIMPs are disfavored by (1) the small scale structure of the universe (i.e. the fact that there aren't enough dwarf satellite galaxies), (2) the exclusion ranges in multiple direct dark matter detection experiments at cross-sections of interactions many orders of magnitude weaker than those of neutrinos, (3) the "cuspy halo" problem (that heavy wimp dark matter doesn't naturally distribute itself in the shapes necessary to match observed galactic rotation curves), and (4) the non-detection of particles in the appropriate mass ranges at particle accelerators like the LHC.
A determination that the directional source of the Fermi line gamma-rays is inconsistent with dark matter just adds one more independent line of experimental data to the others.
While the refutation of the ASM-02 positron excess as a possible dark matter annihilation signal at 300 GeV or more isn't yet complete, the astronomy data problems with cold dark matter apply to particles this heavy with especially great force, and there is other circumstantial evidence (such as the fact that other things we would expect to discovery at the same time as the annihilation of a dark matter particle that heavy) have not been seen. Cosmic rays from quasars continue to be a more plausible source for this signal.
A personal conjecture
For what it is worth, my own intuition, informed by studies that disfavor dark matter models with more than one kind of dark matter particle in any significant frequency, is that a warm dark matter sterile neutrino, if there is one, is not a right handed neutrino in the usual sense, but is instead a singlet particle that is taxonomically part of the gravity sector in a gravi-weak unification theory or some other particle outside the domain of the three Standard Model forces and their interactions, rather than a missing piece within the SU(3)*SU(2)*U(1) group structure of the Standard Model that has almost nothing to do with any Standard Model particle other than the Higgs boson (which might interact with dark matter since it seems to couple to mass).
Also, while warm dark matter is the best prospect in the dark matter paradigm, I believe that it is still hasty to rule out theories outside that paradigm. The best runner up would be some sort of gravity modification, possibly rooted in quantum gravity effects or limitations on the wavelengths of gravity waves as a result of the finite size of the universe. Another would be that the phenomena attributed to dark matter actually consist, at least in part, of multiple kinds of "dim matter" phenomena consisting of ordinary matter, quite possibly maintained in some sort of dynamic equilibrium by ill understood astronomy processes, particularly in galactic clusters and/or galaxy formation, about which we have the least solid understanding.
4 comments:
The Milky Way's halo is curved spacetime
Aether has mass. Aether physically occupies three dimensional space. Aether is physically displaced by matter. There is no such thing as non-baryonic dark matter anchored to matter. Matter moves through and displaces the aether.
'NASA's Voyager Hits New Region at Solar System Edge'
http://www.nasa.gov/home/hqnews/2011/dec/HQ_11-402_AGU_Voyager.html
"Voyager is showing that what is outside is pushing back. ... Like cars piling up at a clogged freeway off-ramp, the increased intensity of the magnetic field shows that inward pressure from interstellar space is compacting it."
It is not the particles of matter which exist in quantities less than in any vacuum artificially created on Earth which are pushing back and exerting inward pressure toward the solar system.
It is the aether, which the particles of matter exist in, which is the interstellar medium. It is the aether which is displaced by the matter the solar system consists of which is pushing back and exerting inward pressure toward the solar system.
'Galactic Pile-Up May Point to Mysterious New Dark Force in the Universe'
http://www.wired.com/wiredscience/2013/01/musket-ball-dark-force/
"The reason this is strange is that dark matter is thought to barely interact with itself. The dark matter should just coast through itself and move at the same speed as the hardly interacting galaxies. Instead, it looks like the dark matter is crashing into something — perhaps itself – and slowing down faster than the galaxies are. But this would require the dark matter to be able to interact with itself in a completely new an unexpected way, a “dark force” that affects only dark matter."
A 'new dark force' is more speculative than understanding space itself has mass. What is occurring is analogous to the bow waves of two boats which pass by each other. The aether displaced by the galaxies interacts and 'piles-up' as the galaxies pass by each other.
'Ether and the Theory of Relativity by Albert Einstein'
http://www-groups.dcs.st-and.ac.uk/~history/Extras/Einstein_ether.html
"the state of the [ether] is at every place determined by connections with the matter and the state of the ether in neighbouring places"
The state of the aether at every place determined by connections with the matter and the state of the aether in neighboring places is the state of displacement of the aether.
'Hubble Finds Ghostly Ring of Dark Matter'
http://www.nasa.gov/mission_pages/hubble/news/dark_matter_ring_feature.html
"Astronomers using NASA's Hubble Space Telescope got a first-hand view of how dark matter behaves during a titanic collision between two galaxy clusters. The wreck created a ripple of dark mater, which is somewhat similar to a ripple formed in a pond when a rock hits the water."
The 'pond' consists of aether. The analogy are two boats which pass by each other very closely. Their bow waves slosh back and forth and create a ripple in the water.
The Milky Way's halo is what is referred to as the curvature of spacetime.
The Milky Way's halo is the state of displacement of the aether.
The geometrical representation of gravity as curved spacetime physically exists in nature as the state of displacement of the aether.
Displaced aether pushing back and exerting inward pressure toward matter is gravity.
@mpc755
I am not going to criticize or affirm the accuracy of your aether hypothesis on the merits. Professional physicists come up with hypotheses at least as radical in published theory all the time.
I will, however, make a couple of observations.
* First, from a P.R./marketing/credibility perspective, it is hard to imagine a worse choice of name for the medium of space-time than aether which is associated very strongly with a late 19th century/early 20th century hypothesis that has long since been definitively disproven with experimental evidence. While many "new physics" modern gravitation/dark energy/dark matter theories proposed by professional physicists (and indeed GR itself) treat the fabric of space-time of something that has properties rather than "nothing", using the term "aether" for that medium is the rhetorical equivalent of calling yourself a crackpot, which is a perception that I not believe that you are intentionally attempting to broadcast to people who read about your hypothesis. Sometimes is makes sense to embrace a word that has become a slur (e.g. "gay" and "lesbian"), but this is not one of those times.
When professional physicists wish to express the notion that space-time itself may give rise to gravitational or inertia effects or consider other foundational re-thinkings of the mechanism of these effects they generally speak of the "inherent curvature of space-time", the cosmological constant, "vacuum energy", "dark energy", "quintessence", scalar fields such as the Higgs field and the inflaton, "superfluid vaccum theory", "Le Sage gravity," "Bose-Einstein condensates" and "Mach's principal". "Aether" has connotations that make it basically a dirty word in reputable discussions physics. Using it in a physics paper is a bit like writing an official government report in 2013 that uses the word "Nigger" describe African-Americans and "Gook" to describe Asian Americans. It has been many decades since anyone would ever do that and destroys your credibility before you have a chance to make a point about the legitimate physics idea that you want to express.
* Second, I owe it to my readers to make clear that the aether hypothesis you propose does not, by any name, have any notable adherents among professional scientists at this time. Dark matter, the quintessence version of "dark energy", various loop quantum gravity theories, and several versions of modified gravity theories all have significant numbers of adherents among professional scientists. Verlinde's entropic gravity hypothesis has some vague similarities to your idea, but it too is not really an aether theory.
*Third, the Voyager phenomena that was observed is well understood and is electro-magnetic rather than gravitional in origin. It is completely different in kind from the musket ball cluster and dark ring phenomena that have been observed by astronomers in the popular press articles that you cite.
You don't consider Robert B. Laughlin, Nobel Laureate in Physics, endowed chair in physics, Stanford University a professional scientist?
"It is ironic that Einstein's most creative work, the general theory of relativity, should boil down to conceptualizing space as a medium when his original premise [in special relativity] was that no such medium existed [..] The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum. . . . Relativity actually says nothing about the existence or nonexistence of matter pervading the universe, only that any such matter must have relativistic symmetry. [..] It turns out that such matter exists. About the time relativity was becoming accepted, studies of radioactivity began showing that the empty vacuum of space had spectroscopic structure similar to that of ordinary quantum solids and fluids. Subsequent studies with large particle accelerators have now led us to understand that space is more like a piece of window glass than ideal Newtonian emptiness. It is filled with 'stuff' that is normally transparent but can be made visible by hitting it sufficiently hard to knock out a part. The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo." - Robert B. Laughlin, Nobel Laureate in Physics, endowed chair in physics, Stanford University
"If a hidden sub-quantum medium is assumed, knowledge of its nature would seem desirable. It certainly is of quite complex character. It could not serve as a universal reference medium, as this would be contrary to relativity theory." - Louis de Broglie, Nobel Laureate in Physics
"According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense." - Albert Einstein, Nobel Laureate in Physics
The relativistic ether referred to by Laughlin is the hidden sub-quantum medium referred to by de Broglie is the ether which propagates light referred to by Einstein.
'Comment on the higher derivative Lagrangians in relativistic theory'
http://arxiv.org/pdf/1305.5759.pdf
"The relativistic theory of an Aether was discussed several time, see for e.g. [8], [9]. In this paper, our hypothesis is different and gives a relativistic theory of the deformation of continuous media (for which the geometry is described by the metric field)."
The Milky Way's halo is the deformation of continuous media. The Milky Way's halo is curved spacetime. The Milky Way's halo is evidence of the correctness of relativity. The Milky Way's halo is the state of displacement of the aether.
'Fluidic Electrodynamics: On parallels between electromagnetic and fluidic inertia'
http://arxiv.org/abs/1202.4611
"It is shown that the force exerted on a particle by an ideal fluid produces two effects: i) resistance to acceleration and, ii) an increase of mass with velocity. ... The interaction between the particle and the entrained space flow gives rise to the observed properties of inertia and the relativistic increase of mass. ... Accordingly, in this framework the non resistance of a particle in uniform motion through an ideal fluid (D’Alembert’s paradox) corresponds to Newton’s first law. The law of inertia suggests that the physical vacuum can be modeled as an ideal fluid, agreeing with the space-time ideal fluid approach from general relativity."
The relativistic mass of an object is the mass of the object and the mass of the aether connected to and neighboring the object which is displaced by the object. The faster an object moves with respect to the state of the aether in which it exists the greater the displacement of the aether by the object the greater the relativistic mass of the object.
The relativistic mass of the Milky Way is the mass of the Milky Way and the mass of the aether connected to and neighboring the Milky Way which is displaced by the matter the Milky Way consists of.
The relativistic mass of the Milky Way accounts for the speed at which the matter in the Milky Way moves.
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