  Bogoliubov's description of Bose gases relies on the linear dynamics of
noninteracting quasiparticles on top of a homogeneous condensate. Here, we
theoretically explore the weakly-nonlinear regime of a one-dimensional photon
superfluid in which phonon-like elementary excitations interact via their
backreaction on the background flow. The generalized dispersion relation
extracted from spatiotemporal intensity spectra reveals additional branches
that correspond to bound Bogoliubov quasiparticles -- phase-locked collective
excitations originating from nonresonant harmonic-generation and wave-mixing
processes. These mechanisms are inherent to fluctuation dynamics and highlight
non-trivial scattering channels other than resonant interactions that could be
relevant in the emergence of dissipative and turbulent phenomena in
superfluids.
