The electron electric dipole moment (EDM) d_e is a representation of the charge distribution within an electron. Within the standard model of elementary particle physics, such a dipole is predicted to be of smaller than 10⁻⁴⁰ e·cm^[1], where e stands for the elementary charge. The existence of a nonzero electron electric dipole moment would imply a violation of both parity invariance and time reversal invariance.^[2] The Particle Data Group publishes its value as 0.07±0.07×10⁻²⁶ e·cm. The most recent experiment performed at the University of California at Berkeley placed an upper bound on (with a 90% confidence level) of |d_e| < 1.6×10⁻²⁷ e·cm.^[3]

Many extensions to the Standard Model have been proposed in the past two decades. These extensions generally predict larger values for the electron EDM. For instance, the various technicolor models predict d_e that ranges from 10⁻²⁷ to 10⁻²⁹ e·cm.^{[citation needed]} Supersymmetric models predict that |d_e| < 10⁻²⁶ e·cm.^[4] The present experimental limit is therefore close to eliminating some of these theories. Further improvements, or a positive result, would place further limits on which theory takes precedence.

[edit] References

1. ^ Hoogeveen, F. (1990). "The standard model prediction for the electric dipole moment of the electron". Nuclear Physics B 341: 322. doi:10.1016/0550-3213(90)90182-D. 
2. ^ Khriplovich, I. B.; Lamoreaux, S. K. (1997). CP Violation Without Strangeness: Electric Dipole Moments of Particles, Atoms, and Molecules. Springer-Verlag. 
3. ^ Regan, B. C.; Commins, E. D.; Schmidt, C. J.; Demille, D. (2002). "New Limit on the Electron Electric Dipole Moment". Physical Review Letters 88: 071805. doi:10.1103/PhysRevLett.88.071805. 
4. ^ Arnowitt, R.; Dutta, B.; Santoso, Y. (2001). "Supersymmetric phases, the electron electric dipole moment and the muon magnetic moment". Physical Review D 64: 113010. doi:10.1103/PhysRevD.64.113010.