![]() The others are Nima Arkani-Hamed of the Institute for Advanced Study (who is also a Perimeter Distinguished Visiting Research Chair), Jacob Bourjaily of Harvard, Alexander Goncharov of Yale, Alexander Postnikov of MIT, and Jaroslav Trnka of Princeton. “Is it possible to describe the interaction of physical particles using only physical particles? The new answer is: yes.”Ĭachazo is part of a small group of mathematical physicists who have developed a new scheme to do just that. “It is natural to ask if virtual particles are strictly necessary,” says Cachazo. ![]() Instead, they are said to represent virtual particles – particles whose momenta are physically impossible. But the internal lines in Feynman diagrams – the ones tracing “particles” that are neither input nor output – do not actually represent physical particles. Anyone looking at a Feynman diagram might get the impression that the diagram is telling a story of particles interacting. Where does the redundancy in Feynman diagrams come from? In a nutshell: virtual particles. Calculating scattering amplitudes is central to that prediction – and the redundancy in the Feynman diagram approach to scattering amplitudes has, until now, been a major stumbling block. In order to discover new phenomena, though, it is necessary to first precisely calculate what current theoretical models predict about particle interactions at very high energies – you can’t spot the unusual unless you know exactly what the usual looks like. At CERN and elsewhere, researchers smash together subatomic particles at high energies, looking for new particles and forces not accounted for in the Standard Model of physics. These problems can now only be handled using powerful computers – and for complex collisions, like the ones happening at the LHC supercollider, they are beyond the reach of the best supercomputers.Ī more efficient process for calculating scattering amplitudes is, therefore, at the top of every particle physicists’ wish list. Calculating what happens when massless particles such as gluons collide, for example, requires hundreds of Feynman diagrams even in simple events where just two gluons interact to produce a few more.Įach of these hundreds of diagrams produces many terms in the formula this makes it infeasible to do these calculations by hand. ![]() The trouble is “all possible diagrams” can be many, many diagrams. You have to add up all the possible diagrams to show that the probability for those physically impossible states is actually zero. But all this comes at a cost: Feynman diagrams contain a large amount of redundancy.”ĭiagram by diagram, Feynman diagrams can produce as final states particles that are physically impossible. Also, they make locality, one of the two pillars of quantum field theory, manifest along the computation. “They work very well they have allowed us to test the predictions of quantum field theory to incredible accuracy. “Feynman diagrams were and are a dream come true,” says Cachazo. Visual and simple, Feynman diagrams have become the standard way to get an intuitive handle on what would otherwise be a rather abstruse calculation. Generations of researchers since have used Feynman diagrams to help them calculate what happens when two or more particles collide, a process generally known as scattering. It was 65 years ago that Richard Feynman introduced his diagrams to the world, simplifying the way physicists model particle interactions. “Well,” Perimeter Faculty member Freddy Cachazo modestly replies, “That’s a provocative question. ![]() Is this the new face of Feynman diagrams? ![]()
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