A bstract The purely on-shell approach to effective field theories requires the construction of
independent contact terms. Employing the little-group-covariant massive-spinor formalism,
we present the first systematic derivation of independent four-point contact terms involving
massive scalars, spin-1/2 fermions, and vectors. Independent three-point amplitudes are
also listed for massive particles up to spin-3. We make extensive use of the simple relations
between massless and massive amplitudes in this formalism. Our general results are …

The purely on-shell approach to effective field theories requires the construction of
independent contact terms. Employing the little-group-covariant massive-spinor formalism,
we present the first systematic derivation of independent four-point contact terms involving
massive scalars, spin-1/2 fermions, and vectors. Independent three-point amplitudes are
also listed for massive particles up to spin-3. We make extensive use of the simple relations
between massless and massive amplitudes in this formalism. Our general results are …