Extra Dimensions and the strong CP problem.
In higher dimensional theories, such as brane world models with quasilocalized non-Abelian gauge fields, the vacuum structure turns out to be trivial. Since the gauge theory behaves at large distances as a 4 + delta dimensional, thus the topology of the infinity is that of S(3+delta) rather than S(3). This topology does not support finite action instantonic configurations and thus the CP violating theta term vanishes on the brane world volume. As well there are no contributions to the straight theta term from the higher dimensional solitonic configurations. In this way, the strong CP problem is absent in the models with quasilocalized gluons.
Chaichian
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High Energy Physics Division, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014 Helsinki, Finland. Masud.Chaichian@helsinki.fi
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