Li Lin Yang

Renormalization-group improved predictions for top-quark pair production at hadron colliders

Precision predictions for phenomenologically interesting observables such as the

Two-loop divergences of massive scattering amplitudes in non-abelian gauge theories

t\bar{t}

Higgs boson self-coupling measurements using ratios of cross sections

invariant mass distribution and forward-backward asymmetry in top-quark pair production at hadron colliders require control over the differential cross section in perturbative QCD. In this paper we improve existing calculations of the doubly differential cross section in the invariant mass and scattering angle by using techniques from soft-collinear effective theory to perform an NNLL resummation of threshold logarithms, which become large when the invariant mass M of the top-quark pair approaches the partonic center-of-mass energy

Higgs boson pair production at the LHC in the

\sqrt {{\hat{s}}}

b \bar{b} W^+ W^-

. We also derive an approximate formula for the differential cross section at NNLO in fixed-order perturbation theory, which completely determines the coefficients multiplying the singular plus distributions in the variable

channel

\left( {1 - {{{{M^2}}} \left/ {{\hat{s}}} \right.}} \right)

Origin of the Large Perturbative Corrections to Higgs Production at Hadron Colliders

. We then match our results in the threshold region with the exact results at NLO in fixed-order perturbation theory, and perform a numerical analysis of the invariant mass distribution, the total cross section, and the forward-backward asymmetry. We argue that these are the most accurate predictions available for these observables at present. Using MSTW2008NNLO parton distribution functions (PDFs) along with αs(MZ) = 0.117 and mt = 173.1 GeV, we obtain for the inclusive production cross sections at the Tevatron and LHC the values

Two-loop divergences of QCD scattering amplitudes with massive partons.

{{{\sigma }}_{\text{Tevatron}}} = \left( {6.30\pm 0.19_{ - 0.23}^{ + 0.31}} \right){\text{pb}}

RG-improved single-particle inclusive cross sections and forward-backward asymmetry in

and σLHC = (149 ± 7 ± 8) pb, where the first error results from scale variations while the second reflects PDF uncertainties.

t\bar t

The infrared divergences of QCD scattering amplitudes can be derived from an anomalous dimension Γ, which is a matrix in color space and depends on the momenta and masses of the external partons. It has recently been shown that in cases where there are at least two massive partons involved in the scattering process, starting at two-loop order Γ receives contributions involving color and momentum correlations between three (and more) partons. The three-parton correlations can be described by two universal functions F1 and f2. In this paper these functions are calculated at two-loop order in closed analytic form and their properties are studied in detail. Both functions are found to be suppressed like (m4/s2) in the limit of small parton masses, in accordance with mass factorization theorems proposed in the literature. On the other hand, both functions are (1) and even diverge logarithmically near the threshold for pair production of two heavy particles. As an application, we calculate the infrared poles in the q → t and gg → t scattering amplitudes at two-loop order.