Top quark interactions and the search for new physics

A complete characterization of all the possible effective interactions up to dimension five of the top and bottom quarks with the electroweak gauge bosons have been made within the context of the nonlinear chiral Lagrangian. The dimension-five operators (19 in total) can contribute to the $V_L{V}_L\to t\overline{t}$ or $t\overline{b}$ amplitudes with a leading energy power of $E^3$ ${(E}^2)$ for fermion pairs with same (opposite) sign helicities. Because of the equivalence between the longitudinal weak boson and the corresponding would-be Goldstone boson in high energy collisions (Goldstone equivalence theorem), they are sensitive to the electroweak symmetry-breaking sector. We also show the top quark production rates at the CERN LHC and the LC via $V_L{V}_L$ fusion processes. At the LC, if no anomalous production rate is found, these coefficients can be bound (based on the naive dimensional analysis) to be of order ${10}^{-1}$. This is about an order of magnitude more stringent than the bounds for the next-to-leading-order bosonic operators commonly studied in $V_L{V}_L\to V_L{V}_L$ scatterings. The effects on a $\mathrm{CP}$-odd observable are also briefly discussed.