Spin-1/2 XX chains with three-spin interactions

We consider a spin-1/2 XX chain with three-spin interactions which is equivalent to a system of noninteracting spinless fermions. We examine some dynamic quantities of the spin model. In particular,we calculate analytically the dynamic transverse (zz) structure factor which is governed by a two-fermion excitation continuum. Moreover,we compute numerically the dynamic xx structure factor which, is a many-fermion dynamic quantity. We illustrate how the three-spin interactions manifest themselves in the dynamic probes.