Bootstrapping multiparton loop amplitudes in QCD

We present a new method for computing complete one-loop amplitudes, including their rational parts, in nonsupersymmetric gauge theory. This method merges the unitarity method with on-shell recursion relations. It systematizes a unitarity-factorization bootstrap approach previously applied by the authors to the one-loop amplitudes required for next-to-leading order QCD corrections to the processes e⁺e^-→Z,γ*→4 jets and pp→W+2 jets. We illustrate the method by reproducing the one-loop color-ordered five-gluon helicity amplitudes in QCD that interfere with the tree amplitude, namely A5;1(1^-,2^-,3⁺,4⁺,5⁺) and A5;1(1^-,2⁺,3^-,4⁺,5⁺). Then we describe the construction of the six- and seven-gluon amplitudes with two adjacent negative-helicity gluons, A6;1(1^-,2^-,3⁺,4⁺,5⁺,6⁺) and A7;1(1^-,2^-,3⁺,4⁺,5⁺,6⁺,7⁺), which uses the previously-computed logarithmic parts of the amplitudes as input. We present a compact expression for the six-gluon amplitude. No loop integrals are required to obtain the rational parts.