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Matthew Tamsett | USLHC | USA

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Why Frank loves SUSY

This week I’ve been in Arlington Texas, attending the excellent south western ATLAS analysis jamboree. As a special treat the jamboree dinner was held in conjunction with an event at Southern Methodist University just to the north of Dallas.

The key speaker at this event was Frank Wilczek, the 2004 winner of the Nobel prize in physics. Frank won this prize for work he began during his Ph.D. studies (take note all you students) concerning the nature of the strong force. Tonight though, he did not talk about this, instead he focused on the LHC and on its ability to discover Supersymmetry (SUSY).

 

Me and Frank Wilczek

Me and Frank Wilczek

 

I’ve name dropped SUSY before, and once again explaining SUSY is way beyond the scope of what I intend to say today. In brief, SUSY solves a number of problems present in the Standard Model by introducing a new symmetry to the theory which allows the transformation of force particle (bosons) into matter particles (fermions). Essentially presenting these as two facets of the same thing.

SUSY has a lot of interesting and beautiful implications. It brings a greater level of symmetry to the Standard Model and by doing so explains all of the known particles and forces in a concise and elegant way.

Frank’s favourite property of SUSY is its ability to explain the strong, weak and electromagnetic forces each as manifestations of a single “grand-unified” force. These forces then only appear to be different to us as we’re forced to study them at the exceptionally low energies available in everyday life. However, if we were to look at these forces more closely, that is to say at much much higher energy, then SUSY predicts that we’d see that they are all one and the same thing.

The motivation for this grand-unification claim comes from, among other things, studying the how the strengths of these forces change with increasing energy. The idea being that if they are all the same force, then at some energy their strengths should all be the same.

If the Standard Model is the final word then this doesn’t happen. But, if we throw SUSY into the equation then, miraculously, it does. Moreover it happens at an energy that fits nicely(-ish) into our understanding of the universe.

 

The evolution of the strengths of the forces with energy in the Standard Model (1).

 

 

The evolution of the strengths of the forces with energy in the Minimal Supersymmetric Standard Model (1). Gravity is also shown in red.

 

Unfortunately even with the LHC studying the unification energy is way way out of reach. But, if SUSY is able to provide grand unification, then we’ll certainly be able to see it at the LHC.

Whether you buy this as a suitable motivation for SUSY or not is a matter of taste. Not everyone is convinced, one of the reason being that to get to the unification scale you have to extrapolate the strengths of the various forces over thirteen orders of magnitude. Yet, to date, we’ve only measured them over the first three.

Frank, however, doesn’t seem to feel this is an issue and as he’s the one with the Nobel prize maybe you should listen to him.

References:

[1] Anticipating a New Golden Age, Frank Wilczek, arXiv:0708.4236v3.

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One Response to “Why Frank loves SUSY”

  1. Luboš Motl says:

    The number of SUSY-related articles from collider insiders today has recorded a 2.5-sigma excess which could indicate that they know something new – linked to the total luminosity which has surpassed 300/pb per detector. See also the promotion of Jay Wacker et al. SUSY methods in the Symmetry Breaking Magazine.

    Too bad that there also exist hints to think that it is just a fluke, indeed. ;-)

    Otherwise, the big desert needed for the extrapolation of couplings to work – and implicitly believed by Wilczek – is a totally sensible qualitative hypothesis. It’s far from obvious that there should be “something” in the observable spectrum in between MSSM and GUT. Well, it’s also far from obvious that there shouldn’t be anything.

    A fair Bayesian treatment must surely assign comparable prior probabilities to both of these qualitatively distinct, not-excluded possibilities. When it’s done, the gauge coupling unification itself is a nontrivial argument that strengthens the probability of the big desert.

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