The Electron Anomalous Magnetic Moment as a Bound on Torsion Couplings

The electron anomalous magnetic moment is the most precisely measured and calculated quantity in physics, and it is natural to ask what it says about torsion. An axial torsion background along the axis of a Penning trap shifts the electron's spin precession while leaving its cyclotron motion unchanged, so a fraction of any torsion signal appears as a shift of the measured anomaly. This paper performs the conversion. The comparison of measurement and theory for the electron anomaly, at an absolute uncertainty of 3e-13, corresponds to a spin-precession shift of 0.283 radians per second at a cyclotron frequency of 1.5e11 Hz, and hence to a bound on an axial torsion background of 9.43e-10 per metre. The muon anomaly, known absolutely to 2e-10 at a ring frequency of 1.5e09 Hz, gives 6.29e-09 per metre. These bounds are ten orders of magnitude weaker than comagnetometer bounds on the same quantity, and the paper explains why: the anomaly is a ratio taken against an enormous orbital frequency, so its celebrated relative precision converts into a modest absolute precession sensitivity. The exercise also yields a methodological warning: the torsion sourced by the trap's own materials is zero in Einstein-Cartan theory, so the g-2 bound applies only to background or extension fields, never to the contact torsion of the minimal theory. Computed from stated assumptions, not measured.