6 strings theory6/15/2023 ![]() What happens in such a world? What do the equations of the corresponding quantum field theory predict? Fig. The only difference is that instead of having three “flavors” of low-mass quarks - up, down and strange - imagine a world that has eight. Modifying the Strong Nuclear Force: Additional Low-Mass Quarksįirst, let’s talk about a case very similar to the imaginary world of Figure 1. To illustrate some of the issues, I’m going to give you some examples of imaginary worlds described by quantum field theories that don’t appear in the Standard Model, and tell you something of what we do and don’t know about them. Theories of a similar type have a role to play in “condensed matter” physics, and if we understood quantum field theory thoroughly, it might allow for a number of the most difficult puzzles in that subject to be resolved. But at a certain level, we already know the answer is “no, it’s not academic”. Is this merely an academic problem of no interest for the real world? That is partly a question of whether any of these poorly understood quantum field theories actually is playing a role in particle physics… which is something we may not know until we complete our study of nature many centuries hence. As far as we can tell, much (if not most) of quantum field theory remains deeply mysterious. But this would be far, far from the truth. Our success with the Standard Model might give you the impression that we basically understand quantum field theory and how to make predictions using it, with a few exceptions. ![]() But that only works if you know what those objects are in the real world we know from experiment that those objects are pions and other low-mass hadrons, but generally we don’t know what they are. Fig 1: The idealized, imaginary world whose quantum field theory is used to make computer simulations of the real-world strong-nuclear force.Īnother method I mentioned involves the use of an effective quantum field theory which describes the “objects” that the original theory produces at low energy. Unfortunately, computer simulations still are nowhere near powerful enough for the calculation of some of the most interesting processes in nature… and won’t be for a long time. And their results allow us, for instance, to understand why quarks and anti-quarks and gluons form the more complex particles called hadrons, of which protons and neutrons are just a couple of examples. (See Figure 4 of Part 4 for more details.) This makes the calculations a lot simpler. the three heavier types of quarks are also ignored.the electron, muon, tau, neutrinos, W, Z and Higgs particles are ignored.the weak nuclear force and the electromagnetic force are turned off,.More precisely, we simulate in a simplified version of the real world, the imaginary world shown in Figure 1 below, where ![]() One class of methods involves directly simulating, using a computer, the behavior of the quantum field theory equations for the strong nuclear force. Specifically, for processes involving the strong nuclear force, in which the distances involved are larger than a proton and the energies smaller than the mass-energy of a proton, some other method is needed. When forces are very “strong”, however, this method doesn’t work. When forces are “weak”, in the technical sense, calculations can generally be done by a method of successive approximation (called “perturbation theory”). I’ve explained in earlier posts how we can calculate many things in the quantum field theory that is known as the “Standard Model” of particle physics, itself an amalgam of three, simpler quantum field theories.
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