arXiv subjects

Chuan-Tsung Chan

Publications and source records attributed to Chuan-Tsung Chan.

39 records · Page 3Linked to original sources

arXiv1999

Nucleon Electric Dipole Moments from QCD Sum Rules

The electric dipole moments of nucleons (NEDM, d_N) are calculated using the method of QCD sum rules. Our calculations are based on the parity and time reversal violating parameter $\thetabar$ in QCD and establish a functional dependence of the NEDM on $\thetabar$, without assuming a perturbative expansion of this symmetry breaking parameter. The results obtained from the QCD sum rules approach are shown to be consistent with the general symmetry constraints on CP violations in QCD, including the necessity of: (1) finite quark masses, (2) spontaneous chiral symmetry breaking, and (3) the U_A(1) anomaly. Given the current experimental upper bound on the neutron electric dipole moment (nEDM), d_n < 10^(-25) e-cm, we find | \thetabar | < 10^(-9). This result is compatible with previous calculations of nEDM using different techniques and excludes the possibility of solving the strong CP problem within QCD via a dynamical suppression mechanism.

hep-ph↗

arXiv1997

On the Symmetry Constraints of CP Violations in QCD

Three symmetry constraints on the CP violations in QCD are discussed in this paper. In order to generate CP violating observables from QCD, these constraints require: (1) spontaneous chiral symmetry breaking, (2) explicit chiral symmetry breaking, e.g., finite quark masses, (3) $U_A(1)$ anomaly, in addition to a nonzero $\thetabar$ parameter. A pictorial illustration is used to unify and elucidate these constraints and indicate a dual relation between quark mass and the quark condensate. Based on the symmetry constraints, a dynamical suppression scenario to solve the strong CP problem within QCD is examined. We conclude that a solution of the strong CP problem has to involve physics beyond the standard model.

hep-ph↗

arXiv1994

Pi- Eta Mixing from QCD Sum Rules

The $q^2$ dependence of the $π$-$η$ mixing amplitude is examined with the use of QCD sum rules. The linear slope of the mixing function $θ(q^2)$ is found to be much smaller than that for $ρ$-$ω$ mixing. Thus the mixing amplitude is approximately the same in the space-like region as in the time-like one, and one may neglect the $q^2$ dependence of the mixing. A comparison between a hadron-meson, an effective chiral model, and the QCD sum rules approaches is made.

hep-ph↗