December 3rd, 2012 by Michael Ricciardi
It was perhaps particle physics’ most elegant and aesthetically appealing theory of (almost) everything: Super Symmetry (SUSY). SUSY, a type of gauge theory developed over the past thirty years, was an ambitious attempt to integrate elementary particle physics with a broader theoretical understanding of the cosmos — an attempt to approach a ‘Theory of Everything.’
The theory posited ‘super partner particles’ — exotic particles that accompany every known particles and what provide the ‘symmetry’ in super symmetry — that would indirectly confirm such controversial ‘New Physics’ theories as String Theory.
But with recent high energy collision experiments at the Large Hadron Collider (LHC) producing (most likely) the fabled Higgs Boson — but none of the partner particles expected to appear within the energies ranges utilized — physicists are now having to reconsider one of their most prized theoretical models of the universe.
SUSY Fails the Test
According to physicist Mikhail Shifman, a once enthusiastic advocate of SUSY and author of an essay published on arXiv.org,, “…nature apparently doesn’t want it. At least, not in its original form.” [quote source]
Shifman’s comment would seem to leave the door open for modifications of the theory.
Indeed, with the failure of the LHC to find any of these “exotic particles” — which might have upended the Standard Model — many physicists have been seeking ways to modify SUSY to account for these failures, while trying to preserve the more powerful features of SUSY.
Reluctance to abandon SUSY is understandable, as it provides explanations for three lasting question in cosmology and theoretical physics: it posits a class of particles that may comprise dark matter*, it unifies three of the fundamental forces (weak, strong, electromagnetism) at high energies, and it solves the Hierarchy Problem — a long-standing physics conundrum involving differences in parameters between mathematical prediction and experimental outcome.
But in his essay, Shifman is critical of these efforts to developed “contrived baroque-like aesthetically unappealing modifications”. The reality is that the theory has failed the experimental tests. Shifman thus urges his colleagues to “start thinking and developing new ideas.”
* called neutralinos, a type of Weakly-interacting Massive Particle (WiMP)
Where to go from here?
With the Standard Model of Physics (virtually) certainly confirmed with the tentative discovery of the Higgs boson*, the fears of many physicists — that there is nothing more to find beyond the Standard Model — have become real.
The disappointing results form the latest collider experiments were presented recently at the Hadron Collider Physics conference in Kyoto, Japan, and with them went many cherished theories that might have “unified the fields”, or some of them.
These results eliminated yet another class of (newer) super symmetry models as well as other theories of the “new physics” (which would include much of String Theory, alas).
Few theories have so dominated physics beyond the Standard Model as SUSY; so much intellectual effort has gone into developing its concepts and equations — and so many other theories have ridden its coat tails — that many physicists see no better theoretical model on the horizon (to build a newer “new physics”)..
From the sound of things, high energy particle physics has come to standstill, of sorts, or perhaps a crossroads.
What is for sure is that these negative findings for SUSY will have wide-ranging impact on the entire field and future of particle physics
In an interview with Sci Am, Dr. Shifman stated “Of course, it is disappointing. We’re not gods. We’re not prophets. In the absence of some guidance from experimental data, how do you guess something about nature?”
The question that now lies before modern physics – and the newest crop of young physicists — is whether to continue forging ahead with the SUSY framework and attempts to modify it, or, to blaze some new theoretical path…to boldly go…
* Three is some new evidence that physicists at the LHC may have discovered two HIggs bosons, at least, they have detected signals at two different energy levels.
Top Photo: (construction of the CMS detector of the LHC and CERN) email@example.com ; CC-By-SA 3.0
Diagram: (Feynman Diagram) VermillionBird ; CC – By 3.0
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