  Bond-percolation graphs are random subgraphs of the d-dimensional integer
lattice generated by a standard bond-percolation process. The associated graph
Laplacians, subject to Dirichlet or Neumann conditions at cluster boundaries,
represent bounded, self-adjoint, ergodic random operators with off-diagonal
disorder. They possess almost surely the non-random spectrum [0,4d] and a
self-averaging integrated density of states. The integrated density of states
is shown to exhibit Lifshits tails at both spectral edges in the
non-percolating phase. While the characteristic exponent of the Lifshits tail
for the Dirichlet (Neumann) Laplacian at the lower (upper) spectral edge equals
d/2, and thus depends on the spatial dimension, this is not the case at the
upper (lower) spectral edge, where the exponent equals 1/2.
