  Multi-particle thermal Casimir interactions are investigated, mostly in terms
of the Casimir entropy, from the point of view based on multiple-scattering
processes. The geometry of the scattering path is depicted in detail, and the
contributions from different types of channels, namely the transverse,
longitudinal and mixing channels, are demonstrated. The geometry of the path
can strongly influence the weight of each channel in the path. Negativity and
nonmonotonicity are commonly seen in the multi-particle Casimir entropy, the
sources of which are diverse, including the geometry of the path, the types of
polarization mixing, the polarizability of each particle, etc. Thermal
contributions from multi-particle scatterings can be significant in the system,
while the zero-temperature multi-particle scattering effects are insignificant.
Limiting behaviors from a multi-particle configuration to a continuum are
briefly explored.
