Two-loop QCD corrections to gluon-gluon scattering

We present the virtual QCD corrections to gluon–gluon scattering due to the interference of tree- and two-loop amplitudes. We work in conventional dimensional regularisation and give analytic expressions renormalised in the scheme. The structure of the infrared divergences agrees with that predicted by Catani while formulae for the finite remainder are given in terms of logarithms and polylogarithms that are real in the physical region. These results, together with those previously obtained for quark–quark and quark–gluon scattering, complete the two-loop matrix elements needed for the next-to-next-to-leading order contribution to inclusive jet production at hadron colliders

The on-shell massless planar double box diagram with an irreducible numerator

Using a Mellin-Barnes representation, we compute the on-shell massless planar double box Feynman diagram with an irreducible scalar product of loop momenta in the numerator. This diagram is needed in calculations of two loop corrections to scattering processes of massless particles, together with the double box without numerator calculated previously by Smirnov. We verify the poles in epsilon of our result by means of a system of differential equations relating the two diagrams, which we present in an explicit form. We verify the finite part with an independent numerical check.Comment: 6 pages, latex, npb.sty, 2 figures (one in postscript); contributed to proceedings of "Loops and Legs in Quantum Field Theory", Bastei, Germany, April 9-14, 200

NLO corrections to differential cross sections for pseudo-scalar Higgs boson production

We have computed the full next-to-leading (NLO) QCD corrections to the differential distributions $d^2\sigma/(dp_T~dy)$ for pseudo-scalar Higgs (A) production at large hadron colliders. This calculation has been carried out using the effective Lagrangian approach which is valid as long as the mass of the pseudo-scalar Higgs boson $m_{\rm A}$ and its transverse momentum $p_T$ do not exceed the top-quark mass $m_t$. The shape of the distributions hardly differ from those obtained for scalar Higgs (H) production because, apart from the overall coupling constant and mass, there are only small differences between the partonic differential distributions for scalar and pseudo-scalar production. Therefore there are only differences in the magnitudes of the hadronic differential distributions which can be mainly attributed to the unknown mixing angle $\beta$ describing the pseudo-scalar Higgs coupling to the top quarks.Comment: 9 pages, LaTeX, 3 Postscript figures In the previous version we have forgotten to include contributions which arrise from interferences between graphs containing vertices corresponding to the operator $O_2(x)$ in Eq. (3) with graphs originating from the operator $O_1(x)$. These interferences occur because of the prescription for the Levi-Civita tensor given in our paper. These extra contributions are added to Eqs. (19) and (20). Numerically they are completely negligible so that the figures are not altere

Two-loop QCD corrections to the scattering of massless distinct quarks.

We present the two-loop virtual QCD corrections to the scattering of distinct massless quarks, , in conventional dimensional regularisation. The structure of the infrared divergences agrees with that predicted by Catani while expressions for the finite remainder are given for each of the s-, t- and u-channels in terms of polylogarithms. The results presented here form a vital part of the next-to-next-to-leading order contribution to inclusive jet production in hadron colliders and will play a crucial role in improving the theoretical prediction for jet cross sections in hadron-hadron collisions

One loop QCD corrections to gluon-gluon scattering at NNLO

We present the O(alphas^4) virtual QCD corrections to gluon-gluon scattering due to the self-interference of the one-loop amplitude. We give analytic expressions renormalised in the MSbar scheme and work in conventional dimensional regularisation. We write the structure of the infrared divergences from direct Feynman diagram evaluation in terms of the Catani formalism for infrared divergences. Formulae for the finite remainder are given in terms of logarithms that are real in the physical region. These results, together with those previously obtained for quark-quark and quark-gluon scattering complete the one-loop matrix elements for 2 to 2 processes needed for the next-to-next-to-leading order contribution to inclusive jet production at hadron colliders.Comment: 17 pages, JHEP clas

Two loop QCD helicity amplitudes for massless quark massless gauge boson scattering

We present the two-loop helicity amplitudes for the scattering of massless quarks and massless gauge bosons in QCD. We use projector techniques to compute the coefficients of the general tensor describing the two-quark two-boson amplitude in conventional dimensional regularisation and use these coefficients to derive the helicity amplitudes in the 't Hooft-Veltman scheme. The structure of the infrared divergences agrees with that predicted by Catani while expressions for the finite remainders for q qbar -> gluon gluon, q qbar -> gluon gamma, q qbar -> gamma gamma and the processes related by crossing symmetry are given in terms of logarithms and polylogarithms that are real in the physical region. We have checked that the interference of tree and two-loop helicity amplitudes, summed over helicities and colours, reproduces the previous results for the finite remainders for interference of tree and two-loop amplitudes given in Refs. [1,2]. We also find agreement with the two-loop helicity amplitudes for quark-gluon scattering presented in Ref. [3]

Two loop QED and QCD corrections to massless fermion boson scattering

We present the NNLO QCD virtual corrections for qurak-antiquark -> gluon photon, quark-antiquark -> photon photon and the NNLO QED virtual corrections for electron positron -> photon photon and all processes related by crossing symmetry. We perform an explicit evaluation of the two-loop diagrams in conventional dimensional regularisation, and our results are renormalised in the MSbar scheme. The infrared pole structure of the amplitudes is in agreement with the prediction of Catani's general formalism for the singularities of two-loop amplitudes, while expressions for the finite remainder are given for all processes in terms of logarithms and polylogarithms that are real in the physical region.Comment: 36 pages, 2 postscript figures, LaTeX, JHEP clas

Two-loop QCD corrections to the scattering of massless distinct quarks

We present the two-loop virtual QCD corrections to the scattering of distinct massless quarks, , in conventional dimensional regularisation. The structure of the infrared divergences agrees with that predicted by Catani while expressions for the finite remainder are given for each of the s-, t- and u-channels in terms of polylogarithms. The results presented here form a vital part of the next-to-next-to-leading order contribution to inclusive jet production in hadron colliders and will play a crucial role in improving the theoretical prediction for jet cross sections in hadron-hadron collisions

Two-loop QCD corrections to the scattering of massless distinct quarks

We present the two-loop virtual QCD corrections to the scattering of distinct massless quarks, , in conventional dimensional regularisation. The structure of the infrared divergences agrees with that predicted by Catani while expressions for the finite remainder are given for each of the s-, t- and u-channels in terms of polylogarithms. The results presented here form a vital part of the next-to-next-to-leading order contribution to inclusive jet production in hadron colliders and will play a crucial role in improving the theoretical prediction for jet cross sections in hadron-hadron collisions

One loop QCD corrections to quark scattering at NNLO

We present the O(as^4) virtual QCD corrections to unlike-quark and like-quark scattering due to the interference of one-loop amplitudes with one-loop amplitudes. The structure of the infrared divergences agrees with that predicted by Catani. The results are expressed in an analytic form so that the relevant expressions for crossed scattering processes can be obtained in a straightforward manner. The one-loop contributions presented here, together with the interference of tree with two-loop amplitudes given recently, complete the 2 to 2 virtual QCD corrections at NNLO for the massless quark scattering processes.Comment: 11 pages, LaTeX using JHEP.cl