  A theory of low temperature (T) electron spin resonance (ESR) in half-integer
spin antiferromagnetic chains is developed using field theory methods and
avoiding previous approximations. It is compared to experiments on Cu benzoate.
Power laws are predicted for the line-width broadening due to various types of
anisotropy. At T -> 0, zero width absorption peaks occur in some cases. The
second ESR peak in Cu benzoate, observed at T<.76K, is argued not to indicate
Neel order as previously claimed, but to correspond to a sine-Gordon "breather"
excitation.
