Abstract
In a non-perturbative gauge-invariant formulation of grand-unified theories all low energy vector states need to be composite with respect to the high-scale gauge group, including the photon. We investigate this by using lattice methods to spectroscopically analyze the vector channel in a toy grand-unified theory, an SU(2) adjoint Higgs model. Our results support indeed the existence of a massless composite vector particle.
Highlights
Observable particles need to be described by manifestly gauge-invariant operators
BRST symmetry is insufficient to ensure this in nonAbelian gauge theories
We find the massless composite vector state, which would act as the photon in a grand unified theories (GUTs) scenario
Summary
Observable particles need to be described by manifestly gauge-invariant operators. Due to a combination of the Brout-Englert-Higgs (BEH) effect together with the Fröhlich-Morchio-Strocchi (FMS) mechanism [1,2] this happens effectively, up to corrections suppressed by powers of the Higgs vacuum expectation value. This has been confirmed in lattice calculations [3,4,5], including subleading contributions [6,7,8], and has potentially experimentally observable consequences [6,8,9,10]. For a review see Ref. [3]
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