Electron electric dipole moment
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The electron electric dipole moment (EDM) <math> d_e </math> is, roughly speaking, a measure 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 <math>10^{-40} \mathrm{\ e\ cm}</math>, 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.
At present time, experimental searches for the electron electric dipole moment have yielded negative results. The most recent experiment performed at the university of California at Berkeley placed an upper bound on (with a 90% confidence level) of:
<math> |d_e| < 1.6 \times 10^{-27}\ \mathrm{e\ cm} </math>
Many extensions to the standard model have been proposed in the past two decades. These extensions genereally predict larger values for the electron EDM. For instance, the various technicolor models predict <math> |d_e| </math> that ranges from <math> 10^{-27} - 10^{-29}\mathrm{e} \ \mathrm{cm} </math>. Supersymmetric models predict that <math> |d_e| \sim < 10^{-26} \mathrm{e} \ \mathrm{cm} </math>.
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 is correct.
Ref. B. Regan, E. Commins, S. Schmidt and D. Demille, Phys. Rev. Lett. 88, 071805 (2002).
