TTP04-01 Next-to-leading mass singularities in two-loop electroweak singlet form factors

We consider virtual electroweak corrections to the form factors for massless chiral fermions coupling to an SU(2)xU(1) singlet gauge boson in the asymptotic region $s\gg M_W^2\sim M_Z^2$, where the invariant mass $s$ of the external gauge boson is much higher than the weak-boson mass scale. Using the sector-decomposition method we compute mass singularities, which arise as logarithms of $s/M_W^2$ and $1/\epsilon$ poles in $D=4-2\epsilon$ dimensions, to one- and two-loop next-to-leading logarithmic accuracy. In this approximation we include all contributions of order $\alpha^l\epsilon^{k}\log^{j+k}(s/M_W^2)$, with $l=1,2$ and $j=2l,2l-1$. We find that the electroweak two-loop leading- and next-to-leading-logarithmic mass singularities can be written in a form that corresponds to a generalization of Catani's formula for massless QCD.