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C. D. White

Publications and source records attributed to C. D. White.

27 records · Page 2Linked to original sources
arXiv2008

Path integral approach to eikonal and next-to-eikonal exponentiation

We approach the issue of exponentiation of soft gauge boson corrections to scattering amplitudes from a path integral point of view. We show that if one represents the amplitude as a first quantized path integral in a mixed coordinate-momentum space representation, a charged particle interacting with a soft gauge field is represented as a Wilson line for a semi-infinite line segment, together with calculable fluctuations. Combining such line segments, we show that exponentiation in an abelian field theory follows immediately from standard path-integral combinatorics. In the non-abelian case, we consider color singlet hard interactions with two outgoing external lines, and obtain a new viewpoint for exponentiation in terms of ``webs'', with a closed form solution for their corresponding color factors. We investigate and clarify the structure of next-to-eikonal corrections.

hep-ph↗
arXiv2008

Single-top hadroproduction in association with a W boson

We present the calculation of the Wt single-top production channel to next-to-leading order in QCD, interfaced with parton showers within the MC@NLO formalism. This channel provides a complementary way of investigating the properties of the Wtb vertex, with respect to the s- and t-channels. We pay special attention to the separation of this process from top quark pair production.

hep-ph↗
arXiv2007

A Global Fit to Scattering Data with NLL BFKL Resummations

We perform a global parton fit to DIS and related data, including next-to-leading logarithmic (NLL) BFKL resummations in both the massless and massive sectors. The resummed fit improves over a standard next-to-leading order (NLO) DGLAP fit, with a positive definite gluon at the input scale as opposed to the negative gluon seen at NLO. Furthermore, the predicted longitudinal structure function is free of perturbative instability at small x, and the reduced cross-section shows a turnover at high y (absent in the NLO fit) consistent with the HERA data.

hep-ph↗
arXiv2006

A Global Fit to Scattering Data with NLL BFKL Resummations

We calculate DIS-scheme splitting and coefficient functions for electromagnetic deep inelastic scattering with small x resummations, as given by the NLL BFKL equation with running coupling and approximate NLL resummed impact factors. The resummations are combined with a NLO fixed order expansion, and the improved quantities thus obtained are stable at small x and significantly suppressed with respect to LL results. These results are implemented in a global fit to DIS and related data, and the results compared to a NLO fixed order DIS-scheme fit and with a previous LL resummed fit. The NLL resummed fit quality is excellent, and constitutes a marked improvement over the purely fixed order approach. The input gluon, at Q_0^2=1GeV^2, obtained from the resummed fit is positive and slightly increasing as x-->0, in contrast to the result obtained at fixed order. A resummed prediction for the longitudinal structure function F_L is presented. It is positive definite and growing with energy at low x and Q^2, where the fixed order results show a significant perturbative instability.

hep-ph↗
arXiv2006

The Virtual Photon-Gluon Impact Factor with Massive Quarks and Exact Gluon Kinematics

We calculate the impact factor coupling a virtual photon to a gluon via a massive quark-antiquark pair at LL order, but with the imposition of the correct gluon kinematics. Exact analytical results are presented in triple Mellin space with respect to scaled Bjorken x, gluon transverse momentum and heavy quark mass. The application of these results to the calculation of approximate NLL coefficient functions needed to relate structure functions to the BFKL gluon is presented. The NLL effects with running coupling are seen to lead to a suppression of the small x divergence when compared with the fixed and running coupling LL results, but less than in the massless case.

hep-ph↗
arXiv2006

The DIS(chi) Scheme for Heavy Quark Production at Small x

In order to successfully describe DIS data, one must take heavy quark mass effects into account. This is often achieved using so called variable flavour number schemes, in which a parton distribution for the heavy quark species is defined above a suitable matching scale. At small x, one must also potentially include high energy corrections to this framework arising from the BFKL equation. We outline the definition of a variable flavour scheme which allows such corrections to be consistently implemented alongside a fixed order QCD expansion. Results of a global fit using this scheme are presented. We also discuss an extension of the resummation to NLL order.

hep-ph↗
arXiv2006

A Variable Flavour Number Scheme for Heavy Quark Production at Small x

We define a new variable flavour number scheme for use in deep inelastic scattering, motivated by the need to consistently implement high energy resummations alongside a fixed order QCD expansion. We define the DIS(chi) scheme at fixed order, and show how to obtain the small x coefficient functions and heavy flavour matrix elements to leading order in the high energy resummation. We then implement these results in a global fit at LO which includes leading resummations with running coupling corrections. Finally, we address the impact of the resummed results on predictions for the longitudinal structure function. We find that they stabilise the behaviour of F_L at small x. Overall, we find that resummations significantly improve the fit to scattering data in the low x regime, although higher orders in the fixed order expansion are needed to describe current structure function and related data over the complete x range.

hep-ph↗
arXiv2005

Comparison of NNLO DIS scheme splitting functions with results from exact gluon kinematics at small x

We consider the effect of exact gluon kinematics in the virtual photon-gluon impact factor at small x. By comparing with fixed order DIS scheme splitting and coefficient functions, we show that the exact kinematics results match the fixed order results well at each order, which suggests that they allow for an accurate NLL analysis of proton structure functions. We also present, available for the first time, x-space parameterisations of the NNLO DGLAP splitting functions in the DIS scheme, and also the longitudinal coefficients for neutral current scattering.

hep-ph↗