Impact of atomic parity violation measurements on precision electroweak physics

The impact of atomic parity violation experiments on the determination of the weak mixing parameter sin²θ and the Peskin-Takeuchi parameters S and T is reassessed in the light of recent electroweak measurements at CERN LEP, SLAC, and Fermilab. Since the weak charge QW provides unique information on S, its determination with a factor of 4 better accuracy than present levels can have a noticeable effect on global fits. However, the measurement of ΔQWQW for two different isotopes provides primarily information on sin²θ. To specify this quantity to an accuracy of ±{}0.0004, comparable to that now provided by other electroweak experiments, one would have to determine ΔQWQW in cesium to about 0.1% of its value, with comparable demands for other nuclei. The relative merits of absolute measurements of QW and isotope ratios for discovering effects of new gauge bosons are noted briefly.