T. Binoth

An automatized algorithm to compute infrared divergent multi-loop integrals

Abstract We describe a constructive procedure to separate overlapping infrared divergences in multi-loop integrals. Working with a parametric representation in D=4−2ϵ dimensions, adequate subtractions lead to a Laurent series in ϵ , where the coefficients of the pole and finite terms are sums of regular parameter integrals which can be evaluated numerically. We fully automatized this algorithm by implementing it into algebraic manipulation programs and applied it to calculate numerically some nontrivial 2-loop 4-point and 3-loop 3-point Feynman diagrams. Finally, we discuss the applicability of our method to phenomenologically relevant multi-loop calculations such as the NNLO QCD corrections for e + e − → 3 jets.

A Full next-to-leading order study of direct photon pair production in hadronic collisions

Abstract. We discuss the production of photon pairs in hadronic collisions, from fixed target to LHC energies. The study which follows is based on a QCD calculation at full next-to-leading order accuracy, including single and double fragmentation contributions, and implemented in the form of a general purpose computer program of “partonic event generator” type. To illustrate the possibilities of this code, we present a comparison with observables measured by the WA70 and D0 collaborations, and some predictions for the irreducible background to the search of Higgs bosons at LHC in the channel

Reduction formalism for dimensionally regulated one-loop N-point integrals

h rightarrow gamma gamma

Next-to-leading order QCD corrections to pp --> b b_bar b b_bar + X at the LHC: the quark induced case

. We also discuss theoretical scale uncertainties for these predictions, and examine several infrared sensitive situations which deserve further study.

Next-to-leading order QCD corrections to pp --> b anti-b b anti-b + X at the LHC: the quark induced case

Abstract We consider one-loop scalar and tensor integrals with an arbitrary number of external legs relevant for multi-parton processes in massless theories. We present a procedure to reduce N-point scalar functions with generic 4-dimensional external momenta to box integrals in (4−2ϵ) dimensions. We derive a formula valid for arbitrary N and give an explicit expression for N=6. Further a tensor reduction method for N-point tensor integrals is presented. We prove that generically higher dimensional integrals contribute only to order ϵ for N≥5. The tensor reduction can be solved iteratively such that any tensor integral is expressible in terms of scalar integrals. Explicit formulas are given up to N=6.

New developments in the 1/N expansion and non-perturbative Higgs physics

Abstract The production of two b b ¯ pairs is a prominent background for Higgs and New Physics searches in various extensions of the Standard Model. We present here the next-to-leading order QCD corrections to the quark induced subprocess using the GOLEM approach for the virtual corrections. We show that our result considerably improves the prediction and conclude that the inclusion of next-to-leading order effects is indispensable for reliable studies of b b ¯ b b ¯ observables in hadronic collisions.

Higgs mass saturation effect and the LHC discovery potential

Abstract The production of two b b ¯ pairs is a prominent background for Higgs and New Physics searches in various extensions of the Standard Model. We present here the next-to-leading order QCD corrections to the quark induced subprocess using the GOLEM approach for the virtual corrections. We show that our result considerably improves the prediction and conclude that the inclusion of next-to-leading order effects is indispensable for reliable studies of b b ¯ b b ¯ observables in hadronic collisions.

A compact representation of the 2 photon 3 gluon amplitude

Abstract We show in this paper that the 1/N expansion is a reliable tool to calculate the properties of a heavy Higgs boson. The 1/N expansion sums up all orders in perturbation theory, and therefore avoids the renormalization scheme dependence of the conventional perturbative approach. It is explained how effects due to the Landau pole of the Higgs sector are isolated and subtracted, and how to perform actual calculations, by computing the Higgs line shape for the processes f f → H → ZZ, f′ f′ at next-to-leading order in the 1/N expansion. The results are compared to the perturbative results to show the agreement between the perturbative and the non-perturbative approach for Higgs masses up to 1 TeV. We conclude that the theoretical predictions for resonant production of a heavy Higgs boson at the LHC are well under control.

A compact representation of the ggg 0 amplitude

Abstract In view of recent perturbative and nonperturbative evidence that the peak of the Higgs resonance saturates as the coupling increases, we examine the potential of the future Large Hadron Collider to discover a heavy Higgs resonance by gluon fusion.

Next-to-leading order QCD corrections to pp -> b(b)over-barb(b)over-bar + X at the LHC: The quark induced case

A compact representation of the loop amplitude gamma gamma ggg -> 0 is presented. The result has been obtained by using helicity methods and sorting with respect to an irreducible function basis. We show how to convert spinor representations into a field strength representation of the amplitude. The amplitude defines a background contribution for Higgs boson searches at the LHC in the channel H -> gamma gamma + jet which was earlier extracted indirectly from the one-loop representation of the 5-gluon amplitude.