V. Ravindran

NNLO corrections to the total cross section for Higgs boson production in hadron–hadron collisions

Abstract We present the next-to-next-to-leading order (NNLO) corrections to the total cross section for (pseudo-) scalar Higgs boson production using an alternative method than those used in previous calculations. All QCD partonic subprocesses have been included and the computation is carried out in the effective Lagrangian approach which emerges from the standard model by taking the limit mt→∞ where mt denotes the mass of the top quark. Our results agree with those published earlier in the literature. We estimate the theoretical uncertainties by comparing the K-factors and the variation with respect to the mass factorization/renormalization scales with the results obtained by lower order calculations. We also investigate the dependence of the cross section on several parton density sets provided by different groups.

Next-to-leading order QCD corrections to differential distributions of Higgs boson production in hadron-hadron collisions

We present the full next-to-leading order corrected differential distributions d 2 σ/dpT /dy, dσ/dpT and dσ/dy for the semi-inclusive process p + p → H + ′ X ′ . Here X denotes the inclusive hadronic state and pT and y are the transverse momentum and rapidity of the Higgs-boson H respectively. All QCD partonic subprocesses have been included. The computation is carried out in the limit that the top-quark mass mt → ∞ which is a very good approximation as long as mH, pT < 200 GeV. Our calculations reveal √

A framework for Higgs characterisation

A bstractWe 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.

Higher-order threshold effects to inclusive processes in QCD

Abstract We present threshold enhanced QCD corrections to inclusive processes such as deep inelastic scattering, Drell–Yan process and Higgs productions through gluon fusion and bottom quark annihilation processes using the resummed cross sections. The resummed cross sections are derived using renormalisation group invariance and mass factorisation theorem that these hard scattering cross sections satisfy and Sudakov resummation of QCD amplitudes. We show how these higher order threshold QCD corrections improve the theoretical predictions for the Higgs production through gluon fusion at hadron colliders.

Mellin moments of the next-to-next-to-leading order coefficient functions for the Drell–Yan process and hadronic Higgs-boson production

Abstract We calculate the Mellin moments of the next-to-next-to-leading order coefficient functions for the Drell–Yan and Higgs production cross sections. The results can be expressed in terms of multiple finite harmonic sums of maximal weight w = 4 . Using algebraic and structural relations between harmonic sums one finds that besides the single harmonic sums only five basic sums and their derivatives w.r.t. the summation index contribute. This representation reduces the large complexity being present in x-space calculations and is well suited for fast numerical implementations.

Two-loop corrections to Higgs boson production

Abstract In this paper we present the complete two-loop vertex corrections to scalar and pseudo-scalar Higgs boson production for general colour factors for the gauge group SU ( N ) in the limit where the top quark mass gets infinite. We derive a general formula for the vertex correction which holds for conserved and non-conserved operators. For the conserved operator we take the electromagnetic vertex correction as an example whereas for the non-conserved operators we take the two vertex corrections above. Our observations for the structure of the pole terms 1 / ɛ 4 , 1 / ɛ 3 and 1 / ɛ 2 in two loop order are the same as made earlier in the literature for electromagnetism. However, we also elucidate the origin of the second order single pole term which is equal to the second order singular part of the anomalous dimension plus a universal function which is the same for the quark and the gluon.

On Sudakov and soft resummations in QCD

Abstract In this article we extract soft distribution functions for Drell–Yan and Higgs production processes using mass factorisation theorem and the perturbative results that are known upto three loop level. We find that they are maximally non-Abelian. We show that these functions satisfy Sudakov type integro-differential equations. The formal solutions to such equations and also to the mass factorisation kernel upto four loop level are presented. Using the soft distribution function extracted from Drell–Yan production, we show how the soft plus virtual cross section for the Higgs production can be obtained. We determine the threshold resummation exponents upto three loop using the soft distribution function.

Direct photon pair production at the LHC to O(αs) in TeV scale gravity models

Abstract The first results on next-to-leading order QCD corrections to production of direct photon pairs in hadronic collisions in the extra dimension models — ADD and RS are presented. Various kinematical distributions are obtained to order α s in QCD by taking into account all the parton level subprocesses. Our Monte Carlo based code incorporates all the experimental cuts suitable for physics studies at the LHC. We estimate the impact of the QCD corrections on various observables and find that they are significant. We also show the reduction in factorization scale uncertainty when O ( α s ) effects are included.

On the Drell–Levy–Yan relation to O(αs2)

We study the validity of a relation by Drell, Levy and Yan (DLY) connecting the deep inelastic structure (DIS) functions and the single-particle fragmentation functions in e^+e^- annihilation which are defined in the spacelike (q^2 0) regions respectively. Here q denotes the momentum of the virtual photon exchanged in the deep inelastic scattering process or the annihilation process. An extension of the DLY-relation, which originally was only derived in the scaling parton model, to all orders in QCD leads to a connection between the two evolution kernels determining the q^2-dependence of the DIS structure functions and the fragmentation functions respectively. In relation to this we derive the transformation relations between the space-and time-like splitting functions up to next-to-leading order (NLO) and the coefficient functions up to NNLO both for unpolarized and polarized scattering. It is shown that the evolution kernels describing the combined singlet evolution for the structure functions F_2(x,Q^2), F_L(x,Q^2) where Q^2=|q^2| or

Unparticle physics at hadron collider via dilepton production

F_2(x,Q^2), \partial F_2(x,Q^2)/\partial \ln(Q^2)