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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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RE: Dark matter is a poor basis to start a theory on
By Ringold on 11/13/2012 1:54:00 PM , Rating: 0
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.

But what is gravity? Have we detected gravitons -- or whatever it is? No. We've got theories, and NASA and ESA are still developing new generations of probes to make further observations, but at the end of the day you can try to make gravity sound like a simple open and shut case but the reality is we see its effects but don't at all know for sure whats going on.

It's why I ended up not doing physics in college and went in to business. The more I scratched the surface, the more I realized physics was a lot of observations that allowed us to estimate the end result of how things interact, but fundamentally we were just bullshitting ourselves and don't know quite a lot.

Not to disparage physics; it's an awesome field of study, extremely important, etc. It's just arrogance, though, to pretend we've got some solid grasp on the basics. Look at the last year; turns out the universe has a maximum resolution, might be a giant hologram. Walk away for 5 years, and everything might change again. (Which is good, but again, we don't have solid answers)


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.


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