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Register a new userContribution of third generation quarks to two-loop helicity amplitudes for W boson pair production in gluon fusion
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Christian Br{\\o}nnum-Hansen
Publication date
2020
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English
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We compute the contribution of third generation quarks ($t, b$) to the two-loop amplitude for on-shell $W$ boson pair production in gluon fusion $gg to WW$. We present plots for the amplitude across partonic phase space as well as reference values for two kinematic points. The master integrals are efficiently evaluated by numerically solving a system of ordinary differential equations.
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We compute the top quark contribution to the two-loop amplitude for on-shell $Z$ boson pair production in gluon fusion, $gg to ZZ$. Exact dependence on the top quark mass is retained. For each phase space point the integral reduction is performed numerically and the master integrals are evaluated using the auxiliary mass flow method, allowing fast computation of the amplitude with very high precision.
We present a complete set of analytic helicity amplitudes for top quark pair production via gluon fusion at two-loops in QCD. For the first time, we include corrections due to massive fermion loops which give rise to integrals over elliptic curves. We present the results of the missing master integrals needed to compute the amplitude and obtain an analytic form for the finite remainders in terms of iterated integrals using rationalised kinematics and finite field sampling. We also study the numerical evaluation of the iterated integrals.
We present a precise and efficient computation of the two-loop amplitudes entering the Higgs boson pair production process via gluon fusion. Our approach is based on the small-Higgs-mass expansion while keeping the full dependence on the top quark mass and other kinematic invariants. We compare our results to the up-to-date predictions based on a combination of sector decomposition and high-energy expansion. We find that our method provides precision numeric predictions in the entire phase space, while at the same time is highly efficient as the computation can be easily performed on a normal desktop or laptop computer. Our method is valuable for practical phenomenological studies of the Higgs boson pair production process, and can also be applied to other similar processes.
We compute the radiative corrections to the four-point amplitude $g+g rightarrow A+A$ in massless Quantum Chromodynamics (QCD) up to order $a_s^4$ in perturbation theory. We used the effective field theory that describes the coupling of pseudo-scalars to gluons and quarks directly, in the large top quark mass limit. Due to the CP odd nature of the pseudo-scalar Higgs boson, the computation involves careful treatment of chiral quantities in dimensional regularisation. The ultraviolet finite results are shown to be consistent with the universal infrared structure of QCD amplitudes. The infrared finite part of these amplitudes constitutes the important component of any next to next to leading order corrections to observables involving pair of pseudo-scalars at the Large Hadron Collider.
We study vector boson pair production at $LHC$ and $SSC$, taking into account the effects generated by the anomalous vector boson and Higgs couplings induced by the operators ${cal O}_W$ and ${cal O}_{UW}$, which are the only dim=6 operators preserving $SU(2)_c$. These operators lead to enhanced production of transverse vector bosons, as opposed to the enhanced production of longitudinal gauge bosons, induced in case $M_Hgsim 1 TeV$, by dim=4 terms already existing in the Standard Model lagrangian. For vector boson pair masses larger than $1 TeV$, we establish very simple approximate expressions for the standard as well as the non-standard helicity amplitudes for $qbar q$ annihilation and vector boson fusion, which accurately describe the physics. These expressions should simplify the experimental search for such interactions. We finally discuss the observability and the disentangling of these interactions.
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