Sunday, August 28, 2022

Antipodes of the standard model

The Feynman diagrams employed in perturbation theory represent particular contributions to the quantum sum over histories. Mathematically, they are integrals full of zeta functions and "polylogarithms" and many other interesting numbers and functions. There is even an algebra of ways to combine the diagrams, since particles exiting one scattering process can enter another; this allows two or more diagrams to be combined into one... In recent decades, this hidden world of mathematical relationships has been intensively studied, under the name of amplitudeology. 

One tool used to simplify these very complicated integrals is the "symbol" of the integral. This is something like a list of the elementary variables and functions appearing in the integral. From this list alone, one can reconstruct a significant part of the integral. 

Late last year, it was discovered that the symbol of one scattering process is the reverse of the symbol of another scattering process. That is, the variables and functions appearing in the path integral of the first process, appear in reverse in the path integral of the second process. This was deeply unexpected. The operation of reversing a symbol is formally a part of the "Hopf algebra" of the Feynman diagrams - there is an "antipode" operator that does this - but no one had envisaged that it might be physically meaningful

The scattering processes involved come from supersymmetric Yang-Mills theory. However, they have counterparts in the standard model, and the standard model counterparts of the antipodally dual amplitudes are also perplexing. One process is just gluons in, gluons out, but the other one has a Higgs involved along with the gluons. Gluons come from QCD, but the Higgs is associated with the electroweak sector and doesn't carry color charge - what is it doing in there? 

At this point I have nothing to say about the pure math of the antipodal duality, but I shall record a few thoughts about the appearance of the Higgs. 

First, let me clear about how this works in super-Yang-Mills theory. The fields in the "N=4" (fourfold extended supersymmetry) super-Yang-Mills theory studied by the amplitudeologists, can be called gluon, gluino, and sgluon. The gluon is a vector field, the gluino is a fermion field, and the sgluon is a scalar field. When this is mapped to the standard model, I assume that gluinos correspond to quarks, and that it's the sgluon which corresponds to the Higgs. 

Second, I'll mention how a Higgs boson is produced by "gluon fusion", in actual interactions that occur in the hadron collider. Basically, gluons fuse to create one side of a top quark loop, and a Higgs is emitted from the opposite vertex... One may approximate this interaction via a direct "gluon-gluon-Higgs" vertex, and I believe this corresponds to a gluon-gluon-sgluon vertex in super-Yang-Mills. \

OK, so, why would an amplitude with a Higgs in it, have a relationship to a pure QCD process? 

In this blog, I have occasionally touched on ways that strong interaction may be related to the electroweak interaction (in ways different from the usual grand unification of both gauge symmetries into a larger simple group). The idea that electroweak interactions could come from gauging the chiral symmetry of the strong interactions, and that this might naturally be so from a higher-dimensional perspective, is one of which I'm very fond. 

Another possibility is that the Higgs is actually toponium, top quark and top antiquark bound by something. Alejandro Rivero's observation that Z0 decay behaves a little like pion decay may be a point in favor of this, given that the Z0 gets its mass from a component of the Higgs field. 

Matti Pitk√§nen has suggested that the apparent color/electroweak duality implied by antipodal duality, might have something to do with the famous electric-magnetic duality of super-Yang-Mills. In this regard, I would draw attention to another idea of Alejandro's that has been mentioned many times in this blog, the "sBootstrap" which aims to derive all the fermions of the standard model, as fermionic superpartners of mesons and diquarks made of the five light flavors of quark. 

Out of many attempts to implement this combinatorial idea within a robust theoretical framework, one of my favorites has been Seiberg duality, in which high-energy N=1 super-QCD, resolves at low energies to a different N=1 gauge theory, in which an extra meson superfield has emerged. The idea here is something like this, that at high energies one has N=1 super-QCD with one heavy quark (the top) and five massless quarks, and that at low energies one has six massive quarks, and an emergent electroweak sector, with the leptons arising as mesino components of the meson superfield... But Seiberg duality is itself a form of electric-magnetic duality. 

All of these might serve as starting points, in a quest to confirm and understand, the possible presence of antipodal duality within the standard model.