  We study the excitation spectrum and dynamical response functions for several
quasi-one-dimensional spin systems in magnetic fields without dipolar spin
order transverse to the field. This includes both nematic phases, which harbor
"hidden" breaking of spin-rotation symmetry about the field and have been
argued to occur in high fields in certain frustrated chain systems with
competing ferromagnetic and antiferromagnetic interactions, and spin density
wave states, in which spin-rotation symmetry is truly unbroken. Using
bosonization, field theory, and exact results on the integrable sine-Gordon
model, we establish the collective mode structure of these states, and show how
they can be distinguished experimentally.
