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Physicists may need new theories to explain how dark matter works

Supersymmetry, or SUSY for short, has been a popular physics theory used to explain away quirks in the Standard Model.  But recent findings from CERN's Large Hadron Collider cast serious doubts on traditional SUSY theory, sending physicists back to the drawing board.

I. Dark Matter -- Does SUSY Offer an Explanation?

When it comes to SUSY, the theory began with a fundamental question -- why were galaxies spinning so fast?

Physicists in the 1900s began to predict the mass of galaxies based on the light of stars within.  What they found was surprising -- the galaxies were spinning faster than they would be if merely adhering to a vanilla version of the Standard Model.

So physicists theorized that the galaxies contained large amounts of so-called "dark matter".  This type of matter is thought to behave in fundamentally different ways from standard matter.  The question facing physicists was how does dark matter behave; physicists sought to solve that question with the theory of super-symmetry, a theory which grew increasingly popular in the particle physics world over the years, spawning several variants.

Dark matter
SUSY is a leading theory to explain the existence of dark matter. [Image Source: NASA]

Under one version of the theory -- the Minimal Supersymmetric Standard Model or MSSM for short -- physicists Howard Georgi (Harvard University) and Savas Dimopoulos (Stanford University) proposed that dark matter consisted of super-particles of masses between 100 GeV and 1 TeV.

The question was how to observe the presence or lack of these high-energy super-particles.  At the time (the 1980s), no particle collider was powerful and sensitive enough to create and detect such pairs.  Then the Large Hadron Collider (LHC) came along.

II. Signs Point to Many SUSY Models Being Flat-Out Wrong

While the LHC is best known for the Higgs boson hunt (scientists currently think they may have observed signs of this much-sought-after particle), the LHC is powerful enough to probe other major unconfirmed physics theories.

SUSY is a perfect example.

The LHC has seven built in particle detectors.  These include flashy detectors like ATLAS and CMS, which have been used in the Higgs boson hunt.

Many popular version of SUSY predict that the "strange" B-meson -- a short-lived 0.5 TeV (in mass) particle that oscillates between a matter and antimater state -- will decay to muons at a far greater rate than the extremely low rate predicted by the vanilla Standard Model.  The source of this shift stems from decay loops such as the chargino and Charged Higgs boson, which SUSY predicts [source] will enhance muon decay rates, by about an order of magnitude.

But it turns out the decay was not as frequent as SUSY expected.  

Bs decay
Bs mu-mu decays occur less frequently than SUSY generally predicts. [Image Source: CERN]

Most detectors failed to observe that kind of decay at all.  And when the LHCb detector finally did spot it, it estimated that only three out of every billion decay results in muon production.

III. Door Opens to New Theories

This at first blush seems an intuitive conclusion -- it would indeed seem odd that the mid-size meson would produce the relatively massive muons on a frequent basis.  But the result does raise major questions -- if SUSY is wrong, what is dark matter made of?

An important thing to note is that while CERN physicists say the new data "squeezes" super-symmetry models, it does not say it invalidates all of them.  For example the so-called AKM model -- theorized by professors Ambrosanio, Kane, Kribs, Martin and Mrenna -- appears to encompass the results in its fringe reaches.

As Prof. Chris Parkes describes to the BBC News, "Supersymmetry may not be dead but these latest results have certainly put it into hospital."
Susy v. SM
SUSY v. SM 2

The observation pushes SUSY to its fringes, raising questions of its validity.
[Image Source: CERN]

Even if the AKM model can accomodate the new results, the fact that they blow up many alternate SUSY models (most of which have over 100 fittable parameters) opens the door to fundamentally different solutions than SUSY to try to explain away symmetry violations.

In other words, the possible fall of SUSY sets the stage for a renaissance of new theory, the kind that equally delights physicists and gives the average member of the public at large a painful headache.

Sources: CERN, BBC News



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Dark matter is a poor basis to start a theory on
By DopeFishhh on 11/13/2012 2:29:48 AM , Rating: 0
I've never liked the dark matter concept, It seems like an idea to explain mismatches between observations and proven theories that got out of hand.

People talk about it like as though it must be there but we don't have much in the way of theories or direct observations to prove or even hint at its existence, kind of like god.




By AnnihilatorX on 11/13/2012 7:50:13 AM , Rating: 1
What is wrong with trying to fix theory when it doesn't explain observation? What else are they going to do? Find some obscure Mathematics plucked out of the blue, make predictions and hope one would fit all reality and hence theory of everything?

So you do not like Newtonian physics, general relativity either because Newton's law was based on observation and general relativity came about because Eistein saw Newton's law did not fit reality?


By bug77 on 11/13/2012 9:34:23 AM , Rating: 2
The guy said the attempt to reconcile theory with observation is what might have gotten out of hand.

I'm not convinced that's he case, but it happened before. In the 19th century, while trying to explain the propagation of light (thought to be just a wave) through the vacuum. A new medium was proposed to explain this: aether. Throughout its existence, this medium earn all sort of crazy properties, in an attempt to match theories and observation. We all know how that ended: there was no aether, but light wasn't just a wave either. Right now, we think dark matter must exist because our observations seem to point to the fact that galaxies should really be much heavier. Just as in the case of light, the correct explanation could be entirely different - but we don't know that yet.

For a reading on aether: http://en.wikipedia.org/wiki/Luminiferous_aether


By drycrust3 on 11/13/2012 10:05:50 AM , Rating: 2
quote:
What is wrong with trying to fix theory when it doesn't explain observation?

What is wrong isn't the "trying to fix" bit, but that the theory "doesn't explain [the] observation" bit. A good theory explains the observation, and it enables predictions that turn out to be true. In fact, one could argue that if you can't make fairly accurate predictions with a theory then it isn't much use.


By inko1nsiderate on 11/13/2012 5:23:36 PM , Rating: 2
Full stop. SUSY was not proposed to solve the Dark Matter problem. SUSY was introduced to solve the Hierarchy problem, or essentially cancel out the quadratic divergences in the Higgs mass to protect the mass of the Higgs from higher energy physics. The Dark Matter candidates in SUSY come from trying to solve the Proton decay problem SUSY brings up. SUSY, without R parity, allows the decay of the Proton to be very large (~15 minutes) and so by introducing R parity this problem was solved. By introducing R parity it also happens to allow a natural description for Dark Matter because odd R parity particles cannot decay into even R parity particles, leading to a potentially stable neutral particle. The breaking of SUSY then allows these odd R parity neutral particles to become WIMPs, and thus potentially explain cosmological Dark Matter.

Now, if we are going to say there is no theoretical understanding of Dark Matter, then we are also going to say something that is flat out wrong. It is very easy to make a model with Dark Matter. Exceedingly easy. So much so that pretty much any given model of physics beyond that Standard Model can have additional Dark Matter particles inserted. For instance, you can make Dark Matter that also leads to Neutrino mass. You can also have Dark Matter from SUSY (coming from R parity), and then add on extra Dark Matter particles (as in other species of Dark Matter or just potential Dark Matter particles with the lightest mass particle of all candidates being the cosmological Dark Matter).


By maugrimtr on 11/13/2012 8:32:33 AM , Rating: 2
Proven theories like Gravity got out of hand? You serious?

The notion is really simple. If you measure all the visible/detectable matter in a Galaxy, you end up being unable to explain that Galaxies gravitational forces and rotation. The only viable solution is to add more matter (i.e. mass) so that our standard models now align correctly with reality. In this case, Gravity and Motion. Two very basic and simple theories which high school physics covers in detail. It's THAT simple which is why the theories themselves are rarely questioned (we can experiment on both exhaustively and those theories unfailingly hold true).

So, where is the missing matter? It must be there. We just can't see it. This is where Dark Matter enters the equation. It's a mumbo-jumbo term for something we don't understand but which we know must exist. It was "invented" in the 1930s by the way! That's when the matter deficit in galaxies was first noticed and written about.

That missing something could be a single form of matter, but it's far more likely to be a whole population of particles we have yet to discover. Since the 1930's we've even discovered some of what the original proportion of required Dark Matter was, e.g. non-emitting bodies (hunks of normal matter which don't emit radiation are effectively invisible to telescopes unless their presence can be inferred indirectly) and neutrinos (teeny tiny particles - countless bazillions of them).

Finally, your whole final paragraph makes no sense. We can observe galaxies, measure them, see their rotations and gravitational effects. Of course, there is evidence that Dark Matter (whatever it actually is) exists. The evidence has existed since 1932 - it's not even remotely controversial.


RE: Dark matter is a poor basis to start a theory on
By Ringold on 11/13/12, Rating: 0
By Stuka on 11/13/2012 5:53:21 PM , Rating: 2
quote:
It's just arrogance, though, to pretend we've got some solid grasp on the basics.


Not to be harsh, but I am highly amused by the notion that science had too much BS, so you went into business. ROFL

Business is rife with vastly more BS and arrogance, VASTLY. Stock prices bounce around based on various and innumerable emotions and social disorders. A ball bounces around based on clearly attainable formulas and definable variables. Science can tell you within a minute variance where an asteroid is going to be 10000 years from now. Business can only give you a 50/50 guess if your restaurant will be profitable in 10 years.

Thanks for the laughs. Good luck to ya out there.


By JediJeb on 11/13/2012 10:20:45 PM , Rating: 2
quote:
Heh, well, don't get too ahead of yourself. Yes, we all know gravity exists and can, with a high degree of accuracy until one starts to get to the quantum level or the scales seen in astronomy, predict how it works.


This is along the lines of what I have been thinking lately about this problem. We try to solve the discrepancy by adding enough mass to make the equations balance out, but what if our measurements of mass are more accurate than we think and it is gravity that still eludes us for explanation? Gravity works well on a planet/moon size system and also on a solar system scale, but we see problems when going smaller to the molecular scale or larger to the galactic scale. I haven't studied it enough so I ask, has anyone even tried to propose that gravity varies with scale, or at least much differently than what has been thought in the past? Maybe the effect of gravity over galactic distances differs by more than 1/D^2, maybe it is much more complex than that. Has anyone tried to make a model that holds mass at what is observed and solves the ratio of gravitational attraction to fit what is observed? Then take this equation down to the molecular level and see if it fits there too?

When looking at gravity as a curvature of spacetime, maybe we have not looked into making the equation to model the curve of the spacetime in a complex enough manner. Does spacetime curve in a linear, quadratic, parabolic, exponent or hyperbolic fashion? Or does it morph from one type to another as distance changes?

Would it not make just as much sense to vary gravity to solve the problem as it does to vary mass, especially since we still do not know exactly what gravity is?


By maugrimtr on 11/14/2012 7:11:52 AM , Rating: 2
What is Gravity? It's one of the fundamental forces of the Universe. It can be reliably measured at almost any scale where it conforms to our current theories each and every time. It's less reliable at the quantum scale because Gravity is, for reasons currently unknown, the weakest fundamental force (it's believed that all fundamental forces were once unified at the Big Bang and of roughly equal strength) and is significantly weaker than the forces acting on an atomic scale. Its weakness is mystifying.

That doesn't explain what it is! Scientists are not that arrogant.

We know it exists, how it works, how to measure it, and how to predict its behavior but we can't quite get that same understanding at the quantum scale - actually, that is one of the greatest mysteries in Physics today. So indeed, science does not actually claim to know what Gravity is. To actually think Scientists are running around arrogantly spinning lies about Gravity is itself arrogance...and ignorance of how the Scientific Method works in real life.

If you want real arrogance, pick a religion and have at it. Independent of whether God exists (I'm Catholic), they've been denying reality for centuries in the face of overwhelming scientific evidence. Once it was whether the Earth was the center of the Universe but these days it's over how life evolved across 3+ Billion years on planet in a 14+ Billion year old Universe.


By tng on 11/14/2012 10:07:29 AM , Rating: 2
quote:
We know it exists, how it works, how to measure it, and how to predict its behavior but we can't quite get that same understanding at the quantum scale - actually, that is one of the greatest mysteries in Physics today.
Exactly!

quote:
To actually think Scientists are running around arrogantly spinning lies about Gravity is itself arrogance...and ignorance of how the Scientific Method works in real life.
Yet many people here on these pages will rate you down for saying that there may be no such thing as Dark Matter, it may still be a function of gravity that is not understood at a larger scale.


RE: Dark matter is a poor basis to start a theory on
By PaFromFL on 11/13/2012 8:42:28 AM , Rating: 1
SUSY is not necessarily threatened by the lack of high-energy dark matter particles. Dark matter may just be some macro-scale cosmological effect better explained by a new general relativity term. SUSY is extremely threatened by a much slower than expected decay rate that suggests intermediate particles may not exist or additional symmetry constraints are needed. With all the adjustable parameters, it may take quite a while to bend SUSY to fit the new data.


By Jaybus on 11/13/2012 4:33:04 PM , Rating: 2
Yes, exactly. Supermassive black holes are being detected in nearly every galaxy looked at. Large stars orbiting very close to M87's black hole will be observed at their closest over the next few years. M87 has jets of plasma emitted from its central black hole, meaning it is spinning. Not just spinning, but calculated to be spinning at over half the speed of light. General relativity predicts that the black hole should be dragging on space-time itself near the spinning black hole. If true, this should have an observable affect on the orbit of these nearby stars. The orbits of these stars around the central black hole should give a much better approximation of the mass of the black hole. Could the missing mass simply be the previously unobservable black hole?

Also, perhaps better observation of galactic black holes will lead to a refined relativity theory. After all, the gravitational singularity, zero volume and infinite density, is by definition the point at which general relativity breaks down and most likely fails to model black holes correctly. We should get a better idea of the mass of the galactic black holes before we decide that there must be a mysterious dark matter aether.


By inko1nsiderate on 11/13/2012 5:29:00 PM , Rating: 1
Full stop. SUSY was not proposed to solve the Dark Matter problem. SUSY was introduced to solve the Hierarchy problem, or essentially cancel out the quadratic divergences in the Higgs mass to protect the mass of the Higgs from higher energy physics. The Dark Matter candidates in SUSY come from trying to solve the Proton decay problem SUSY brings up. SUSY, without R parity, allows the decay of the Proton to be very large (~15 minutes) and so by introducing R parity this problem was solved. By introducing R parity it also happens to allow a natural description for Dark Matter because odd R parity particles cannot decay into even R parity particles, leading to a potentially stable neutral particle. The breaking of SUSY then allows these odd R parity neutral particles to become WIMPs, and thus potentially explain cosmological Dark Matter.

Now, if we are going to say there is no theoretical understanding of Dark Matter, then we are also going to say something that is flat out wrong. It is very easy to make a model with Dark Matter. Exceedingly easy. So much so that pretty much any given model of physics beyond that Standard Model can have additional Dark Matter particles inserted. For instance, you can make Dark Matter that also leads to Neutrino mass. You can also have Dark Matter from SUSY (coming from R parity), and then add on extra Dark Matter particles (as in other species of Dark Matter or just potential Dark Matter particles with the lightest mass particle of all candidates being the cosmological Dark Matter).


By bh192012 on 11/13/2012 7:12:41 PM , Rating: 2
Time to take another look at MOND? (Modified Newtonian dynamics)


"Young lady, in this house we obey the laws of thermodynamics!" -- Homer Simpson














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