116232109
Portrait characteristics of QCD jets
In the framework of the perturbation-theory approach to the description of multihadron production in hard processes we analyze the portrait characteristics of jets (the energy and the multiplicity distribution in an isolated jet) and their influence on each other (drag effects, the azimuthal asymmetry of the jet in an aggregate). In contrast to the common but theoretically unjustified procedure of analyzing multijet events, we develop a consistent approach based on inclusive and calorimetric characteristics.
18934979
Diffractive Higgs production and related processes
We review the signal, and the $b\bar{b}$ background, for Higgs production by the exclusive double-diffractive process, $pp \to p+H+p$, and its subsequent $H \to b\bar{b}$ decay, at the LHC. We discuss the production of Higgs bosons in both the SM and MSSM. We show how the predicted rates may be checked at the Tevatron by observing the exclusive double-diffractiveproduction of dijets, or $\chi_c$ or $\chi_b$ mesons, or $\gamma \gamma$ pairs.
115929216
Three-Reggeon description of inclusive proton spectra
119105262
Impact of the W boson decay width on photon bremsstrahlung accompanying W pair production
Abstract. The bremsstrahlung spectrum of photons accompanying W pair production depends on the decay width of the unstable W bosons. The dependence arises from the interference between emission at different stages of the production and decay process. We present a quantitative discussion of this effect, and consider the implications for measurements at LEP2 and LC energies.
119379184
Radiative corrections to the hadronic cross-section measurement at DA$\Phi$NE
Abstract. The hadronic invariant mass distribution for the process of electron–positron annihilation into a pair of charged pions accompanied by a photon radiated from the initial state has been studied for the region of DA$\Phi$NE energies. The Born cross–section and the electromagnetic radiative corrections to it are calculated for realistic conditions of the KLOE detector. The dependence on the physical parameters which define the event selection is obtained.
123672226
THE STRING EFFECT AND QCD COHERENCE
Abstract In the framework of the idea of local parton-hadron duality we discuss the asymptotic predictions of QCD perturbation theory for angular distributions of hadron flows in three-jet events, e + e - → q q g → hadrons. The coherence of soft gluon emission provides the QCD explanation of the string effect observed in experiments.
14354109
A two-instanton test of the exact solution of N = 2 supersymmetric QCD
Abstract The exact solution of N = 2 supersymmetric QCD found by Seiberg and Witten includes a prediction for all multi-instanton contributions to the low-energy dynamics. In the case where the matter hypermultiplets are massless, the leading non-perturbative contribution at weak coupling comes from the two-instanton sector. We calculate this contribution from first principles using the exact two-instanton solution of the self-dual Yang-Mills equation found by Atiyah, Drinfeld, Hitchin and Manin. We find exact agreement with the predictions of Seiberg and Witten for all numbers of flavours. We also confirm their predictions for the case of massive hypermultiplets.
122485626
Multi-instantons do not stop the cross-section at half the 't Hooft suppression
Abstract Using the (1+1)-dimensional abelian Higgs model as a toy model we study the non-perturbative semiclassical behaviour of the total cross-section in the limit of large Higgs mass mh as compared to the vector boson mass mw. In the single-instanton approximation the total cross-section rises steeply with energy. The leading-order exponential suppression by the 't Hooft factor (twice the instanton action) disappears at energies near the sphaleron energy. Above the sphaleron energy semiclassical methods based on the instanton/anti-instanton valley break down. The influence of multi-instanton contributions is found to be completely negligible up to energies of the order of the sphaleron energy.
8182637
Recursion relations for gauge theory amplitudes with massive particles
We derive general tree-level recursion relations for amplitudes which include massive propagating particles. As an illustration, we apply these recursion relations to scattering amplitudes of gluons coupled to massive scalars. We provide new results for all amplitudes with a pair of scalars and n ≤ 4 gluons. These amplitudes can be used as building blocks in the computation of one-loop 6-gluon amplitudes using unitarity based methods.
118956578
Baryon number violation and instantons in the standard model
We report on the recent developments in the theory of high energy collisions mediated by an instanton. Theoretical methods of studying the nonperturbative dynamics of the Standard Model at high energies in association with multi-particle-production and (B+L)-violation are reviewed. Particularly, we concentrate on the optical theorem approach based on the valley method. A pre-history and a current status of the theory of electroweak (B+L)-violation in high energy collisions are discussed.
119247942
Wilson loops @ 3-loops in special kinematics
A bstractWe obtain a compact expression for the octagon MHV amplitude/Wilson loop at 3 loops in planar $ \mathcal{N} = {4} $ SYM and in special 2d kinematics in terms of 7 unfixed coefficients. We do this by making use of the cyclic and parity symmetry of the amplitude/Wilson loop and its behaviour in the soft/collinear limits as well as in the leading term in the expansion away from this limit. We also make a natural and quite general assumption about the functional form of the result, namely that it should consist of weight 6 polylogarithms whose symbol consists of basic cross-ratios only (and not functions thereof). We also describe the uplift of this result to 10 points.