Lateral projection as a possible explanation of the nontrivial boundary   dependence of the Casimir force
  We find the lateral projection of the Casimir force for a configuration of a sphere above a corrugated plate. This force tends to change the sphere position in the direction of a nearest corrugation maximum. The probability distribution describing different positions of a sphere above a corrugated plate is suggested which is fitted well with experimental data demonstrating the nontrivial boundary dependence of the Casimir force. 
G.L.Klimchitskaya, S.I.Zanette, and A.O.Caride