  We use renormalization-group methods in effective field theory to improve the
theoretical prediction for the cross section for Higgs-boson production at
hadron colliders. In addition to soft-gluon resummation at NNNLL, we also resum
enhanced contributions of the form (C_A\pi\alpha_s)^n, which arise in the
analytic continuation of the gluon form factor to time-like momentum transfer.
This resummation is achieved by evaluating the matching corrections arising at
the Higgs-boson mass scale at a time-like renormalization point \mu^2<0,
followed by renormalization-group evolution to \mu^2>0. We match our resummed
result to NNLO fixed-order perturbation theory and give numerical predictions
for the total production cross section as a function of the Higgs-boson mass.
Resummation effects are significant even at NNLO, where our improved
predictions for the cross sections at the Tevatron and the LHC exceed the
fixed-order predictions by about 13% and 8%, respectively, for m_H=120 GeV. We
also discuss the application of our technique to other time-like processes such
as Drell-Yan production, e^+ e^- --> hadrons, and hadronic decays of the Higgs
boson.
