  Weak interaction of temporal cavity solitons due to gain saturation and
recovery in a delay differential model of a long cavity semiconductor laser is
studied numerically and analytically using an asymptotic approach. It is shown
that in addition to the usual soliton repulsion leading to a harmonic
mode-locking regimes a soliton attraction is also possible in a laser with
nonzero linewidth enhancement factor. It is shown numerically that this
attraction can lead either to a pulse merging or to a pulse bound state
formation.
