  The effective description of the weak interaction between an emitter and a
bosonic field as a sequence of two-body collisions provides a simple intuitive
picture compared to traditional quantum optics methods as well as an effective
calculation tool of the joint emitter-field dynamics. Here, this collisional
approach is extended to many emitters (atoms or resonators), each generally
interacting with the field at many coupling points ("giant" emitter). In the
regime of negligible delays, the unitary describing each collision in
particular features a contribution of a chiral origin resulting in an effective
Hamiltonian. The picture is applied to derive a Lindblad master equation (ME)
of a set of giant atoms coupled to a (generally chiral) waveguide field in an
arbitrary white-noise Gaussian state, which condenses into a single equation
and extends a variety of quantum optics and waveguide-QED MEs. The effective
Hamiltonian and jump operators corresponding to a selected photodetection
scheme are also worked out.
