  Recent high-precision measurements of atomic parity-nonconserving transitions
between the 6S and 7S states of cesium allow for a determination of the weak
nuclear charge with a precision of 1.3%, providing an improved test of the
standard model at low energy. Implications for new physics are examined in
terms of low energy effects on the weak charge, in particular contact
interactions and scalar leptoquark limits. Prospects for further improvements
are described.
