All-Order Corrections To Higgs Boson Production In Association With Jets

We present a new framework for calculating multi-jet observables. The framework is based on the factorisation of scattering amplitudes in the kinematical limit of large invariant mass between all particles. We show that by constraining the analyticity of scattering amplitudes away from this limits, we get good agreement order by order with the full, fixed order perturbative calculation at the low orders where these are available, and therefore get firm predictions on the all-order behaviour. As an example, we study Higgs boson production through gluon fusion in association with at least two jets at the LHC.Comment: Invited talk at 44th Rencontres de Moriond on QCD and High Energy Interactions, La Thuile, Valle d'Aosta, Italy, 14-21 Mar 200

A Closer look at the analysis of NLL BFKL.

The initial analyses of the next-to-leading logarithmic corrections to the BFKL kernel were very discouraging. Encouraged by the success of new methods in the analysis of the BFKL equation at full NLL accuracy we demonstrate in this talk how some of the initial conclusions were based on a breakdown of the tools used in the analysis rather than the framework itself

A New approach to inclusive decay spectra.

The main obstacle in describing inclusive decay spectra in QCD — which, in particular, limits the precision in extrapolating the measured ¯B −→ Xs rate to the full phase space as well as in extracting |Vub| from inclusive measurements of charmless semileptonic decays — is their sensitivity to the non-perturbative momentum distribution of the heavy quark in the meson. We show that, despite this sensitivity, resummed perturbation theory has high predictive power. Conventional Sudakov–resummed perturbation theory describing the decay of an onshell heavy quark yields a divergent expansion. Detailed understanding of this divergence in terms of infrared renormalons has paved the way for making quantitative predictions. In particular, the leading renormalon ambiguity cancels out between the Sudakov factor and the quark pole mass. This cancellation requires renormalon resummation but involves no non-perturbative information. Additional effects due to the Fermi motion of the quark in the meson can be systematically taken into account through power corrections, which are only important near the physical endpoint. This way the moments of the ¯B −→ Xs spectrum with experimentally–accessible cuts — which had been so far just parametrized — were recently computed by perturbative means. At Moriond these predictions were confronted with new data from BaBar

All-Order Corrections and Multi-Jet Rates

We discuss results from a recently proposed all-order description of hard, radiative corrections to certain multi-jet processes at hadron colliders. The description is based on obtaining an all-order estimate of the t-channel singularities of scattering amplitudes. As a simple example, we illustrate the similarities between qQ and qg-scattering. In particular, we discuss how at tree-level, all non-suppressed helicity-amplitudes for these processes consist of a pure t-channel pole. This structure is used in the construction of all-order approximations.Comment: 6 pages. Talk given at RADCOR 2009 - 9th International Symposium on Radiative Corrections (Applications of Quantum Field Theory to Phenomenology), October 25 - 30 2009, Ascona, Switzerlan

A Study of the gluon ladder in diffractive processes.

The solution to the non–forward BFKL equation in the Leading Logarithmic approximation is expressed in terms of a sum of iterations of its kernel directly in transverse momentum and rapidity space. Several studies of the non–forward solution are performed both at the level of the gluon Green’s function and for a toy cross–section, including an analysis of the diffusion properties as found in this approach. The method developed in this paper allows for a direct inspection of the momenta in the BFKL ladder, and can be applied to solving the non–forward BFKL equation to next–to–leading logarithmic accuracy, when the corresponding kernel is available

New possibilities in the study of NLL BFKL.

The high energy limit of scattering processes in QCD is, at least on the purely theoretical level, described by the BFKL equation. However, many phenomenological studies of BFKL fail miserably when confronted with data. In this talk we will briefly review the application of (LL) BFKL in phenomenology, and critically examine the application of LL eigenfunctions in the study of the NLL BFKL kernel. We then introduce a recently proposed iterative solution of the NLL BFKL equation that allows for a detailed study of physical properties of the BFKL evolution

Multi-Jet Processes in the High Energy Limit of QCD.

We discuss how the multi-Regge factorisation of QCD amplitudes can be used in the study of multi-jet processes at colliders. We describe how the next-to-leading logarithmic (NLL) BFKL evolution can be combined with energy and momentum conservation. By recalculating the quark contribution to the next-to-leading logarithmic corrections to the BFKL kernel we can study several properties of the NLL corrections. We demonstrate that in the standard analysis, the NLL corrections to a single gluon emission includes contributions from significantly more energetic quark–anti-quark configurations, something that could contribute to the sizable NLL corrections in the standard BFKL analysis

Solving the BFKL equation in the next-to-leading approximation.

The Balitsky–Fadin–Kuraev–Lipatov equation in the next–to–leading logarithmic approximation is solved using an iterative method. We derive the solution for forward scattering with all conformal spins. A discussion of the infrared finiteness of the results is included

The Gluon Green's function in N=4 supersymmetric Yang-Mills theory.

The high energy limit of scattering amplitudes in the N = 4 supersymmetric Yang– Mills theory is studied by solving the corresponding BFKL equation in the next– to–leading approximation. The gluon Green’s function is analysed using a newly proposed method suitable for investigating the contribution from higher conformal spins. From this new approach complete agreement is obtained with the results of Kotikov and Lipatov on conformal spins and angular dependenc

The Gluon Green's function in the BFKL approach at next-to-leading logarithmic accuracy.

We investigate the gluon Green’s function in the high energy limit of QCD using a recently proposed iterative solution of the Balitsky–Fadin–Kuraev–Lipatov (BFKL) equation at next–to–leading logarithmic (NLL) accuracy. To establish the applicability of this method in the NLL approximation we solve the BFKL equation as originally written by Fadin and Lipatov, and compare the results with previous studies in the leading logarithmic (LL) approximation