Quantum vacuum interaction between two sine-Gordon kinks
  We calculate the quantum vacuum interaction energy between two kinks of the sine-Gordon equation. Using the $TGTG$--formula, the problem is reduced to the known formulas for quantum fluctuations in the background of a single kink. This interaction induces an attractive force between the kinks in parallel to the Casimir force between conducting mirrors. 
M. Bordag and J. M. Munoz-Castaneda
hep-th