Gauge Symmetries Emerging from Extra Dimensions
  We argue that extra dimensions with a properly chosen compactification scheme could be a natural source for emergent gauge symmetries. Actually, some proposed vector field potential terms or polynomial vector field constraints introduced in five-dimensional Abelian and non-Abelian gauge theory is shown to smoothly lead to spontaneous violation of an underlying 5D spacetime symmetry and generate pseudo-Goldstone vector modes as conventional 4D gauge boson candidates. As a special signature, there appear, apart from conventional gauge couplings, some properly suppressed direct multi-photon (multi-boson, in general) interactions in emergent QED and Yang-Mills theories whose observation could shed light on their high-dimensional nature. Moreover, in emergent Yang-Mills theories an internal symmetry G also occurs spontaneously broken to its diagonal subgroups once 5D Lorentz violation happens. This breaking origins from the extra vector field components playing a role of some adjoint scalar field multiplet in the 4D spacetime. So, one naturally has the Higgs effect without a specially introduced scalar field multiplet. Remarkably, when being applied to Grand Unified Theories this results in a fact that the emergent GUTs generically appear broken down to the Standard Model just at the 5D Lorentz violation scale M.   PACS numbers: 11.15.-q, 11.30.Cp, 11.30.Pb, 11.10.Kk 
J.L. Chkareuli and Z. Kepuladze
hep-th hep-ph