Recently I read in an essay by Wilczek:
"Photons are mixtures of weak B3 and hypercharge C mesons. It is those objects, not the emergent photon, whose properties are ideally simple."
Until now I thought that photons are elementary massless spin-1 bosons that arise as gauge bosons for the $U(1)$ symmetry in (quantized) electrodynamics. They can be described by a four-vector $A_\mu$ including two unphysical degrees of freedom that can be eliminated by introducing the gauge-invariant four-rotation $F_{\mu\nu} := \partial_\mu A_\nu - \partial_\nu A_\mu$ so that only the two polarisations (helicity $h = \pm 1$) remain.
Where does the emergence of the photon come from? Is this related to electroweak symmetry breaking and the Higgs field? Why are mesons (hadrons) mentioned??
Answer
Is this related to electroweak symmetry breaking and the Higgs field?
Yes. There is a particular mixture of the $W^0$ and $B$ bosons that propagates freely in the Higgs field condensate; this freely propagating state is the photon.
Why are mesons (hadrons) mentioned??
There was a time when the weak intermediate vector bosons were referred to as "W mesons". For example, see this APS paper from 1964, Mass and Interactions of the W Meson
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