Effective lagrangian description of top production and decay

We propose a rather general description of residual New Physics (NP) effects on the top quark couplings. These effects are described in terms of 20 gauge invariant dim = 6 operators involving gauge and Higgs bosons as well as quarks of the third family. We compute their implications for the γtt̄, Ztt̄ and tbW vertices and study their observability in the process e−e+ → tt̄ with t → bW → blνl. We present results for the integrated cross section, the angular distribution and various decay distribution and polarization asymmetries for NLC energies of 0.5 − 2 TeV . Observability limits are discussed and interpreted in terms of the NP scales associated to each operator through the unitarity constraints. The general landscape of the residual NP effects in the heavy quark and bosonic sectors is also presented. Partially supported by the EC contract CHRX-CT94-0579 and by Ministry of Education, Science and Culture, Japan, under Grant-in-Aid for International Scientific Research Program (No.07044097).