A Chern-Simons Coefficient Bound from Polarisation Rotation over the Distance to Last Scattering

This paper examines what value of a timelike Chern-Simons coefficient, of the kind introduced in the Carroll-Field-Jackiw modification of electrodynamics, would produce the reported rotation, and how tightly the measurement restricts that coefficient. The calculation is performed from stated assumptions and published polarisation measurements, using the deposited script so that every quoted number can be reproduced. The headline outputs are: beta deg = 0.30; k AF eV = 2.41e-36; k AF err eV = 8.83e-37; k AF GeV = 2.41e-45; upper95 eV = 4.14e-36. The treatment separates what the published measurements supply from what a theoretical framework must additionally provide; where a required quantity is not supplied, that absence is reported plainly as a negative result rather than replaced by an assumed value. The study is computed from stated assumptions and published inputs; it is not a new measurement. SIMULATED, NOT MEASURED in the sense that all derived quantities are calculated, not observed.