Dynamical density correlation function of 1D Mott insulators in a   magnetic field
  We consider the one dimensional (1D) extended Hubbard model at half filling in the presence of a magnetic field. Using field theory techniques we calculate the dynamical density-density correlation function $\chi_{nn}(\omega,q)$ in the low-energy limit. When excitons are formed, a singularity appears in $\chi_{nn}(\omega,q)$ at a particular energy and momentum transfer. 
Davide Controzzi (Trieste) and Fabian H.L. Essler (BNL)