Calculation of the transverse parton distribution functions at next-to-next-to-leading order

We describe the perturbative calculation of the transverse parton distribution functions in all partonic channels up to next-to-next-to-leading order based on a gauge invariant operator definition. We demonstrate the cancellation of light-cone divergences and show that universal process-independent transverse parton distribution functions can be obtained through a refactorization. Our results serve as the first explicit higher-order calculation of these functions starting from first principles, and can be used to perform next-to-next-to-next-to-leading logarithmic q T resummation for a large class of processes at hadron colliders

Transverse-momentum resummation for vector-boson pair production at NNLL+NNLO

We consider the transverse-momentum ( p T ) distribution of ZZ and W + W − boson pairs produced in hadron collisions. At small p T , the logarithmically enhanced contributions due to multiple soft-gluon emission are resummed to all orders in QCD perturbation theory. At intermediate and large values of p T , we consistently combine resummation with the known fixed-order results. We exploit the most advanced perturbative information that is available at present: next-to-next-to-leading logarithmic resummation combined with the next-to-next-to-leading fixed-order calculation. After integration over p T , we recover the known next-to-next-to-leading order result for the inclusive cross section. We present numerical results at the LHC, together with an estimate of the corresponding uncertainties. We also study the rapidity dependence of the p T spectrum and we consider p T efficiencies at different orders of resummed and fixed-order perturbation theory

ZZ production at hadron colliders in NNLO QCD

We report on the first calculation of next-to-next-to-leading order (NNLO) QCD corrections to the inclusive production of Z -boson pairs at hadron colliders. Numerical results are presented for pp collisions with centre-of-mass energy ( <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>s</mi></msqrt></math> ) ranging from 7 to 14 TeV. The NNLO corrections increase the NLO result by an amount varying from 11% to 17% as <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>s</mi></msqrt></math> goes from 7 to 14 TeV. The loop-induced gluon fusion contribution provides about <math altimg="si2.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mn>60</mn><mtext>%</mtext></math> of the total NNLO effect. When going from NLO to NNLO the scale uncertainties do not decrease and remain at the <math altimg="si3.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mo>±</mo><mn>3</mn><mtext>%</mtext></math> level

Higgs boson gluon–fusion production at threshold in N 3 LO QCD

We present the cross-section for the threshold production of the Higgs boson at hadron-colliders at next-to-next-to-next-to-leading order (N 3 LO) in perturbative QCD. We present an analytic expression for the partonic cross-section at threshold and the impact of these corrections on the numerical estimates for the hadronic cross-section at the LHC. With this result we achieve a major milestone towards a complete evaluation of the cross-section at N 3 LO which will reduce the theoretical uncertainty in the determination of the strengths of the Higgs boson interactions

Appearance of a Minimal Length in e+e− Annihilation

Experimental data reveal with a 5 σ significance the existence of a characteristic minimal length le=1.57×10−17  cm at the scale E=1.253 TeV in the annihilation reaction e+e−→γγ(γ) . Nonlinear electrodynamics coupled to gravity and satisfying the weak energy condition predicts, for an arbitrary gauge invariant Lagrangian, the existence of spinning charged electromagnetic soliton asymptotically Kerr-Newman for a distant observer with the gyromagnetic ratio g=2 . Its internal structure includes a rotating equatorial disk of de Sitter vacuum which has properties of a perfect conductor and ideal diamagnetic, displays superconducting behavior, supplies a particle with the finite positive electromagnetic mass related to breaking of space-time symmetry, and gives some idea about the physical origin of a minimal length in annihilation

Production of Sterile Neutrino dark matter and the 3.5 keV line

The recent observation of an X-ray line at an energy of 3.5 keV mainly from galaxy clusters has initiated a discussion about whether we may have seen a possible dark matter signal. If confirmed, this signal could stem from a decaying sterile neutrino of a mass of 7.1 keV. Such a particle could make up all the dark matter, but it is not clear how it was produced in the early Universe. In this letter we show that it is possible to discriminate between different production mechanisms with present-day astronomical data. The most stringent constraint comes from the Lyman- α forest and seems to disfavor all but one of the main production mechanisms proposed in the literature, which is the production via decay of heavy scalar singlets. Pinning down the production mechanism will help to decide whether the X-ray signal indeed comprises an indirect detection of dark matter

Light fermionic NNLO QCD corrections to top-antitop production in the quark-antiquark channel

We present the NNLO corrections to top pair production in the quark-antiquark channel proportional to the number of light quark flavors N l . While the double real corrections were derived previously, here we compute the real-virtual and virtual-virtual contributions in this partonic channel. Using the antenna subtraction formalism, we show that the subtraction terms correctly approximate the real-virtual contributions in all their infrared limits. Combined with the integrated forms of the double real and real-virtual subtraction terms, we show analytically that the explicit infrared poles cancel at the real-virtual and virtual-virtual levels respectively, thereby demonstrating the validity of the massive extension of the NNLO antenna formalism. These NNLO corrections are implemented in a Monte Carlo parton level generator providing full kinematical information on an event-by event basis. With this program, NNLO differential distributions in the form of binned histograms are obtained and presented here

Resummation of the transverse-energy distribution in Higgs boson production at the Large Hadron Collider

We compute the resummed hadronic transverse-energy ( E T ) distribution due to initial-state QCD radiation in the production of a Standard Model Higgs boson of mass 126 GeV by gluon fusion at the Large Hadron Collider, with matching to next-to-leading order calculations at large E T . Effects of hadronization, underlying event and limited detector acceptance are estimated using aMC@NLO with the Herwig++ and Pythia8 event generators

Motivic amplitudes and cluster coordinates

In this paper we study motivic amplitudes — objects which contain all of the essential mathematical content of scattering amplitudes in planar SYM theory in a completely canonical way, free from the ambiguities inherent in any attempt to choose particular functional representatives. We find that the cluster structure on the kinematic configuration space Conf n (ℙ 3 ) underlies the structure of motivic amplitudes. Specifically, we compute explicitly the coproduct of the two-loop seven-particle MHV motivic amplitude $\mathcal{A}_{7,2}^{\mathcal{M}}$ and find that like the previously known six-particle amplitude, it depends only on certain preferred coordinates known in the mathematics literature as cluster $\mathcal{X}$ - coordinates on Conf n (ℙ 3 ). We also find intriguing relations between motivic amplitudes and the geometry of generalized associahedrons, to which cluster coordinates have a natural combinatoric connection. For example, the obstruction to $\mathcal{A}_{7,2}^{\mathcal{M}}$ being expressible in terms of classica

Ratios of W and Z cross sections at large boson p T as a constraint on PDFs and background to new physics

We motivate a measurement of various ratios of W and Z cross sections at the Large Hadron Collider (LHC) at large values of the boson transverse momentum ( p T ≳ M W,Z ). We study the dependence of predictions for these cross-section ratios on the multiplicity of associated jets, the boson p T and the LHC centre-of-mass energy. We present the flavour decomposition of the initial-state partons and an evaluation of the theoretical uncertainties. We show that the W + /W − ratio is sensitive to the up-quark to down-quark ratio of parton distribution functions (PDFs), while other theoretical uncertainties are negligible, meaning that a precise measurement of the W + /W − ratio at large boson p T values could constrain the PDFs at larger momentum fractions x than the usual inclusive W charge asymmetry. The W ± /Z ratio is insensitive to PDFs and most other theoretical uncertainties, other than possibly electroweak corrections, and a precise measurement will therefore be useful in validating theoretical predictions needed in data-driven methods, such as using W (→ ℓν) + jets events to estimate the Z (→ ν $\overline{\nu}$ ) + jets background in searches for new physics at the LHC. The differential W and Z cross sections themselves, dσ / d p T , have the potential to constrain the gluon distribution, provided that theoretical uncertainties from higher-order QCD and electroweak corrections are brought under control, such as by inclusion of anticipated next-to-next-to-leading order QCD corrections