Alex Kalloniatis
CSSM
Adelaide
Tuesday, March 22, 3.00pm
Seminar Room, First Floor Physics Building, University of Adelaide
Solving the strong CP problem
Abstract:
Quantum chromodynamics permits an additional CP violating term with a free parameter, theta, which does not contribute in any order of perturbation theory but can only have non-perturbative significance. Using chiral perturbation theory one can show that this theta term leads to CP-violating processes such as the decay of eta mesons to two pions, or an electric dipole moment for the neutron. However the tiny measured bound on this dipole moment sets a correspondingly narrow range for values of the theta parameter in nature, of the order 10^(-9). It seems extraordinary that nature could conspire to tune such a small number unless it were exactly zero. The strong CP problem is thus the question as to why strong interactions generate no detectable CP violation. Two main scenarios exist: either that the lightest quark mass is exactly zero (which seems unlikely), and theta can be rotated out, or that there exist (as yet undetected) non-standard model particles, spinless bosons called "axions".I will show that the domain model which we have developed in recent years, and which accounts for confinement, spontaneous chiral symmetry breaking and resolves the axial U(1) problem, also solves the strong CP problem within QCD. Along the way, I will show that the domain model satisfies numerous other constraints on nonperturbative QCD, such as the anomalous Ward identity of Crewther, and the Witten-Veneziano mechanism for giving the eta-prime meson its mass.
A practical consequence of this is an elegant new formula which can replace the usual anomalous term in effective chiral Lagrangians and which correctly encodes all of the symmetry properties of low energy QCD.