It has been assumed that it is possible to approximate the interactions of
quantized BPS solitons by quantising a dynamical system induced on a moduli
space of soliton parameters. General properties of the reduction of quantu
m systems by a Born-Oppenheimer approximation are described here and applie
d to sigma models and their moduli spaces in order to learn more about this
approximation. New terms arise from the reduction procedure, some of them
geometrical and some of them dynamical in nature. The results are generalis
ed to supersymmetric sigma models, where most of the extra terms vanish. (C
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