Polarisation in sfermion decays:: determining tan β and trilinear couplings

The basic parameters of supersymmetric theories can be determined at future e(+)e(-) linear colliders with high precision. We investigate in this report how polarisation measurements in (tau) over tilde and (t) over tilde or (b) over tilde decays to tau leptons and t quarks plus neutralinos or charginos can be used to measure beta (in particular for large values) and to determine the trilinear couplings A(tau), A(t) and A(b) in sfermion pair production.