Dynamical Structure Factor in Cu Benzoate and other spin-1/2 antiferromagnetic chains

Recent experiments of the quasi-one-dimensional spin-1/2 antiferromagnet Copper Benzoate established the existence of a magnetic field induced gap. The observed neutron scattering intensity exhibits resolution limited peaks at both the antiferromagnetic wave number and at incommensurate wave numbers related to the applied magnetic field. We determine the ratio of spectral weights of these peaks within the framework of a low-energy effective field theory description of the problem.