We introduce a framework, based on an effective field theory approach, that allows one to perform characterisation studies of the boson recently discovered at the LHC, for all the relevant channels and in a consistent, systematic and accurate way. The production and decay of such a boson with various spin and parity assignments can be simulated by means of multi-parton, tree-level matrix elements and of next-to-leading order QCD calculations, both matched with parton showers. Several sample applications are presented which show, in particular, that beyond-leading-order effects in QCD have nontrivial phenomenological implications.

The first results on next-to-leading order QCD corrections to graviton-induced processes in hadron collisions in models of TeV-scale gravity are presented focusing on the case of dilepton pair production inpp and pp collisions. Distributions in the invariant mass Q, the longitudinal fraction x F , the rapidity Y and the forward-backward asymmetry of the lepton pair are studied. The quantitative impact of the QCD corrections for searches of extra dimensions at hadron colliders is investigated. It turns out that at the LHC ( √ S = 14 TeV) the K-factor is rather large (K = 1.6) for large invariant mass Q of the lepton pair, indicating the importance of accounting for these QCD corrections in the experimental search for TeV-scale gravity. At the Tevatron, the K-factor does not substantially deviate from the Standard Model value. However, its inclusion is necessitated to make the cross-section stable with respect to scale variations.PACS numbers: 11.10. Kk, 13.60.Hb. contributions to SM processes strongly suggests that the LO corrections at hadronic colliders are quiet unreliable [6,7]. The standard Drell-Yan (DY) processes and Higgs production at hadron colliders, for example, not only get large corrections but the theoretical uncertainties get reduced significantly from NLO corrections.It is with this motivation that the present paper presents the results of the computation of NLO-QCD corrections to the DY process, P 1 + P 2 → µ + µ − + X, where P 1 , P 2 are initial hadrons and X is an arbitrary hadronic final state. This process takes place via the exchange of γ, Z and graviton. These NLO results are used to study the impact of the QCD correction for this process at the present Tevatron collider and the future LHC which is planned to operate at centre-of-mass energies around 14 TeV. This process had been considered earlier to LO [8,9] in the ADD model.The results we present here are for the ADD model, but since the QCD corrections, presented here, are model-independent they may equally be used for studying the Randall-Sundrum model of warped compactification [10].This paper is organised as follows. In Sec. 2 we describe additional graviton vertices needed to perform the NLO QCD corrections. We study the distributions in the invariant mass Q (Sec. 3), the longitudinal fraction x F (Sec. 4), the rapidity Y (Sec. 5) and the forward-backward asymmetry (Sec. 6) of lepton pair. Finally in Sec. 7 we present the discussion and summarise the results. In Appendix A and B we present the detailed expressions needed for x F and Y distributions in Sec. 4 and Sec. 5 respectively.

The coupling of a pseudo-scalar Higgs boson to gluons is mediated through a heavy quark loop. In the limit of large quark mass, it is described by an effective Lagrangian that only admits light degrees of freedom. In this effective theory, we compute the threeloop massless QCD corrections to the form factor that describes the coupling of a pseudoscalar Higgs boson to gluons. Due to the axial anomaly, the pseudo-scalar operator for the gluonic field strength mixes with the divergence of the axial vector current. Working in dimensional regularization and using the 't Hooft-Veltman prescription for the axial vector current, we compute the three-loop pseudo-scalar form factors for massless quarks and gluons. Using the universal infrared factorization properties, we independently derive the three-loop operator mixing and finite operator renormalisation from the renormalisation group equation for the form factors, thereby confirming recent results in the operator product expansion. The finite part of the three-loop form factor is an important ingredient to the precise prediction of the pseudo-scalar Higgs boson production cross section at hadron colliders. We discuss potential applications and derive the hard matching coefficient in soft-collinear effective theory.

We consider the production of a pseudo-scalar particle A at the LHC, and present accurate theoretical predictions for its inclusive cross section in gluon fusion. The prediction is based on combining fixed-order perturbation theory and all-order threshold resummation. At fixed order we include the exact next-to-next-to-leading order (NNLO) plus an approximate next-to-next-to-next-to-leading order (NLO) which is based on the recent computation at this order for the scalar case. We then add threshold resummation at next-to-next-to-next-to leading logarithmic accuracy (NLL). Various forms of threshold resummation are considered, differing by the treatment of subleading terms, allowing a robust estimate of the theoretical uncertainties due to missing higher orders. With particular attention to pseudo-scalar masses of 200 and 750 GeV, we also observe that perturbative convergence is much improved when resummation is included. Additionally, results obtained with threshold resummation in direct QCD are compared with analogous results as computed in soft-collinear effective theory, which turn out to be in good agreement. We provide precise predictions for pseudo-scalar inclusive cross section at 13 TeV LHC for a wide range of masses. The results are available through updated versions of the public codes ggHiggs and TROLL.