In QED these two processes have to be added because they correspond to two distinct Feynman diagrams, while, according to DHS duality, each one provides, for strong interactions, the whole story. In the other process the pair a+c exchanges a virtual particle with the pair b+d. In one process, a+b fuse to form a metastable state (a resonance) which, after a characteristic lifetime, decays into c+d. It relates two apparently distinct processes contributing to an elementary reaction, say a+b → c+d. The basic idea was to impose on the S-matrix a property now known as Dolen–Horn–Schmid (DHS) duality. Not at all! I was taking a bottom-up approach to understand the strong interaction. Is it true that your “eureka” moment was when you came across the Euler beta function in a textbook? It was also looking very conventional but, eventually, led to something even more revolutionary than QCD – the idea that hadrons are actually strings. The S-matrix, which relates the initial and final states of a quantum-mechanical process, allows one to directly calculate the probabilities of scattering processes without solving a quantum field theory such as QED. No one was ready for such a logical jump, so we tried something else: an S-matrix approach. The highly non-trivial jump from QED to QCD meant having the guts to write a theory for entities (quarks) that nobody had ever seen experimentally. (Image credit: CERN-PHOTO-201807-183-1.)īut things weren’t so clear back then. Veneziano, photographed at CERN in July, worked at CERN for more than 30 years and led the theory division between 19. But even more disturbing was that there were so many (and ever growing in number) different species of hadrons that we felt at a loss with field theory – how could we cope with so many different states in a QED-like framework? We now know how to do it and the solution is called quantum chromodynamics (QCD). One reason was the strength of the strong coupling compared to the electromagnetic one. We had an example of a relativistic quantum theory that worked: QED, the theory of interacting electrons and photons, but it looked hopeless to copy that framework for the strong interactions. ![]() In the mid-1960s we theorists were stuck in trying to understand the strong interaction. What led you to the 1968 paper for which you are most famous? He was trying to explain the strong interaction, but his paper wound up marking the beginning of string theory. ![]() In the summer of 1968, while a visitor in CERN’s theory division, Gabriele Veneziano wrote a paper titled “Construction of a crossing-symmetric, Regge behaved amplitude for linearly-rising trajectories”.
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