Single top quark production at hadron colliders allows a direct measurement of the top quark charged current coupling. We present the complete tree-level helicity amplitudes for four processes involving the production and semileptonic decay of a single top quark: W -gluon fusion, flavor excitation, s-channel production and W associated production. For the first three processes we study the qual...

The Weyl–van-der-Waerden spinor technique for calculating helicity amplitudes of massive and massless particles is presented in a form that is particularly well suited to a direct implementation in computer algebra. Moreover, we explain how to exploit discrete symmetries and how to avoid unphysical poles in amplitudes in practice. The efficiency of the formalism is demonstrated by giving explic...

The Higgs couplings to matter fields are proportional to their masses. Thus Higgs amplitudes can be obtained by differentiating amplitudes without Higgs with respect to masses. We show how this well-known statement can be extended to higher order when renormalization effects are taken into account. We establish the connection with the Callan-Symanzik and renormalization group equations and cons...

Humans perform visual search fairly efficiently, finding targets within only a few fixations. Data from eye-tracked participants was subjected to a fixation by fixation analysis to pinpoint why participants tended to make fewer fixations than would be expected by chance. The goal of this paper is to present a computational model that performs visual search as efficiently as humans. The model va...

A general continuum-RPA approach is developed to describe electromagnetic transitions between giant resonances. Using a diagrammatic representation for the three-point Green’s function, an expression for the transition amplitude is derived which allows one to incorporate effects of mixing of single and double giant resonances as well as to take the entire basis of particle-hole states into cons...

In this paper, we will expound upon the concepts proffered in [5], where we proposed an information theoretic approach to intelligence in the computational sense. We will examine data and meme aggregation, and study the effect of limited resources on the resulting meme amplitudes.

Hadronic phases in ππ and KK̄ channels are calculated à la Regge. At the D mass one finds δππ ≃ π3 and δKK̄ ≃ −π6 in good agreement with the CLEO data while at the B mass these angles are predicted to be, respectively, 11◦ and -7◦. With the hadronic phase eKK̄ taken into account, a quark diagram decomposition of the isospin invariant amplitudes in D → KK̄ decays fits the data provided the exchange ...

The branching ratios and CP asymmetries of B → ππ decays measured in B factory experiments indicate a large ratio of color-suppressed (C) to color-allowed (T ) tree contributions and a large relative phase between the tree and penguin amplitude. In this talk, I would like to report on a recent analysis to see whether the large C/T ratio can be explained within the QCD based model with i) a larg...

We compute the part of the two-loop virtual amplitude for the process gg → V1V2 → (l1 l̄ ′ 1)(l2 l̄ ′ 2), where V1,2 are arbitrary electroweak gauge bosons, that receives contributions from loops of massless quarks. Invariant masses of electroweak bosons are allowed to be different from each other. Our result provides an important ingredient for improving the description of gluon fusion contribut...

Helicity amplitudes for the γ * N → ∆ transition are calculated using the cloudy bag model. A correction for center-of-mass motion is carried out using a modified Peierls-Thouless projection method. This reduces the magnitude of the transition amplitudes at small momentum transfer and enhances them at modest momentum transfers. Our calculation shows that the pion cloud contributes substantially...