Abstract
Fermion compositeness and other new physics can be signalled by the presence of a strong four-fermion contact interaction. Here we present a study of ℓℓqq and ℓℓℓ′ℓ′ contact interactions using the reactions: ℓ+ℓ−→ℓ′+ℓ′−,bb¯,cc¯ at future e+e− linear colliders with s√=0.5−5 TeV and μ+μ− colliders with s√=0.5,4 TeV. We find that very large compositeness scales can be probed at these machines and that the use of polarized beams can unravel their underlying helicity structure