Physics impact of a precise determination of the top quark mass at an e+e- linear collider -: art. no. 075

At a prospective e(+)e(-) Linear Collider (LC) a very precise determination of the top quark mass with an accuracy of deltam(t) less than or similar to 100 MeV will be possible. This is to be compared with the envisaged accuracy of deltam(t) = 1-2 Gev at the Tevatron and the LHC. We discuss the physics impact of such a precise determination of m(t), focusing on the Standard Model (SM) and its minimal supersymmetric extension (MSSM). In particular, we show the importance of a precise knowledge of m(t) for electroweak precision observables, and for Higgs physics and the scalar top sector of the MSSM. Taking the mSUGRA model as a specific example, we furthermore demonstrate the importance of a precise m(t) value for the prediction of sparticle masses and for constraints on the parameter space allowed by the relic density. The uncertainty in m(t) also significantly affects the reconstruction of the supersymmetric high scale theory. We find that going from hadron collider to LC accuracy in m(t) leads to an improvement of the investigated quantities by up to an order of magnitude.