Speaker
Description
The strong CP problem arises from the apparent smallness of the QCD theta parameter, which is experimentally constrained to satisfy |theta| <~ 10^-10 despite being allowed by the local symmetries of the Standard Model. In this talk I revisit the conceptual assumptions underlying the theta-dependent formulation of QCD, with particular emphasis on the role of topology, global gauge structure, and the definition of topological charge in the continuum theory.
I discuss the distinction between local topological-density correlations, which are essential for known nonperturbative QCD phenomena such as the eta-prime mass and topological susceptibility, and the stronger assumption that the continuum functional integral must be fundamentally decomposed into globally classified smooth topological sectors. The analysis suggests that a vanishing theta parameter is consistent with a formulation of QCD based only on local gauge invariance and causal locality, while the conventional form of the strong CP problem arises after introducing additional global structure.
The implications for axion physics and nonperturbative QCD will also be briefly discussed.