22 research outputs found
Factorisation and Subtraction beyond NLO
We provide a general method to construct local infrared subtraction
counterterms for unresolved radiative contributions to differential cross
sections, to any order in perturbation theory. We start from the factorised
structure of virtual corrections to scattering amplitudes, where soft and
collinear divergences are organised in gauge-invariant matrix elements of
fields and Wilson lines, and we define radiative eikonal form factors and jet
functions which are fully differential in the radiation phase space, and can be
shown to cancel virtual poles upon integration by using completeness relations
and general theorems on the cancellation of infrared singularities. Our method
reproduces known results at NLO and NNLO, and yields substantial
simplifications in the organisation of the subtraction procedure, which will
help in the construction of efficient subtraction algorithms at higher orders.Comment: 34 pages, 3 figure
A fresh look at the nested soft-collinear subtraction scheme: NNLO QCD corrections to N-gluon final states in annihilation
We describe how the nested soft-collinear subtraction scheme [1] can be used to compute the next-to-next-to-leading order (NNLO) QCD corrections to the production of an arbitrary number of gluonic jets in hadron collisions. We show that the infrared subtraction terms can be combined into recurring structures that in many cases are simple iterations of those terms known from next-to-leading order. The way that these recurring structures are identified and computed is fairly general, and can be applied to any partonic process. As an example, we explicitly demonstrate the cancellation of all singularities in the fully-differential cross section for the → X + Ng process at NNLO in QCD. The finite remainder of the NNLO QCD contribution, which arises upon cancellation of all ϵ-poles, is expressed via relatively simple formulas, which can be implemented in a numerical code in a straightforward way. Our approach can be extended to describe arbitrary processes at NNLO in QCD; the largest remaining challenge at this point is the combinatorics of quark and gluon collinear limits
A fresh look at the nested soft-collinear subtraction scheme: NNLO QCD corrections to N -gluon final states in q q ÂŻ annihilation
We describe how the nested soft-collinear subtraction scheme [1] can be used to compute the next-to-next-to-leading order (NNLO) QCD corrections to the production of an arbitrary number of gluonic jets in hadron collisions. We show that the infrared subtraction terms can be combined into recurring structures that in many cases are simple iterations of those terms known from next-to-leading order. The way that these recurring structures are identified and computed is fairly general, and can be applied to any partonic process. As an example, we explicitly demonstrate the cancellation of all singularities in the fully-differential cross section for the qq¯ → X + Ng process at NNLO in QCD. The finite remainder of the NNLO QCD contribution, which arises upon cancellation of all ϵ-poles, is expressed via relatively simple formulas, which can be implemented in a numerical code in a straightforward way. Our approach can be extended to describe arbitrary processes at NNLO in QCD; the largest remaining challenge at this point is the combinatorics of quark and gluon collinear limits
A fresh look at the nested soft-collinear subtraction scheme: NNLO QCD corrections to -gluon final states in annihilation
We describe how the nested soft-collinear subtraction scheme [1] can be used
to compute the next-to-next-to-leading order (NNLO) QCD corrections to the
production of an arbitrary number of gluonic jets in hadron collisions. We show
that the infrared subtraction terms can be combined into recurring structures
that in many cases are simple iterations of those terms known from
next-to-leading order. The way that these recurring structures are identified
and computed is fairly general, and can be applied to any partonic process. As
an example, we explicitly demonstrate the cancellation of all singularities in
the fully-differential cross section for the process at
NNLO in QCD. The finite remainder of the NNLO QCD contribution, which arises
upon cancellation of all -poles, is expressed via relatively simple
formulas, which can be implemented in a numerical code in a straightforward
way. Our approach can be extended to describe arbitrary processes at NNLO in
QCD; the largest remaining challenge at this point is the combinatorics of
quark and gluon collinear limits.Comment: 116 pages, 9 appendices, 1 figure, alphabetic inde
Non-factorisable contribution to t-channel single-top production
We compute the non-factorisable corrections to t-channel single-top quark production at the LHC. These peculiar corrections arise because of interactions between the heavy- and the light-quark lines and appear for the very first time at next-to-next-to-leading order in perturbative QCD. We find that the non-factorisable corrections change the single-top production cross section and the relevant kinematic distributions in this process by about half a percent
Local Analytic Sector Subtraction at NNLO
We present a new method for the local subtraction of infrared divergences at
next-to-next-to-leading order (NNLO) in QCD, for generic infrared-safe
observables. Our method attempts to conjugate the minimal local counterterm
structure arising from a sector partition of the radiation phase space with the
simplifications following from analytic integration of the counterterms. In
this first implementation, the method applies to final-state massless
particles. We show how our method compactly organises infrared subtraction at
NLO, we deduce in detail the general structure of the subtraction terms at
NNLO, and we provide a proof of principle with a complete application to a
simple process at NNLO.Comment: Matching journal version, minor correction
Local analytic sector subtraction for final state radiation at NNLO
We present recent developments of the local analytic sector subtraction of
infrared singularities for final state real radiation at NNLO in QCD.Comment: 10 page