Upper bounds on the charge susceptibility of many-electron systems   coupled to the quantized radiation field
  We extend the Kubo-Kishi theorem concerning the charge susceptibility of the Hubbard model in the following way: (i) The electron-photon interaction is taken into account. (ii) Not only on-site but also general Coulomb repulsion is considered. 
Tadahiro Miyao
math-ph math.MP