  We construct 2-solitons of any speed of the focusing energy-critical
nonlinear wave equation in dimension 5. The existence result also holds for the
case of K-solitons, for any K >2, assuming that the speeds are collinear. The
main difficulty of the construction is the strong interaction between the
solitons due to the slow spatial decay of the single soliton. This is in
contrast with previous constructions of multi-solitons for other nonlinear
models (like generalized KdV and nonlinear Schrodinger equations in energy
subcritical cases), where the interactions are exponentially small in time due
to the exponential decay of the solitons.
