56466072
Angular distribution of particle flows and perturbative QCD predictions
Abstract. We discuss the predictions of perturbative QCD for angular flows of final state particles in two and three jet events including their cms energy and jet resolution (ycut) dependence. The simple analytical formulae for gluon bremsstrahlung from primary partons, modified for gluon cascading, reproduce the main features of the experimental data well. For ycut-selected events, the particle flow is derived from a superposition of colour dipoles in much the same way that photon radiation is derived from electric dipoles.
124029542
On the sensitivity of the inclusive distributions in parton jets to the coherence effects in QCD gluon cascades
The KNO multiplicity distributions and properties of two-particle correlations in QCD jets are considered in the framework of the perturbative approach accounting for effects of the coherence in the soft gluon bremsstrahlung.
125850380
Multiple Hadron Production in Parton {QCD} Jets
117871006
Pomeron universality from identical pion correlations at the LHC
Abstract Bose–Einstein correlations of identical pions produced in high-energy pp collisions at the LHC allow a probe of the Pomeron exchange mechanism. The size of the domain which emits the pions depends on the multiplicity of events, but not on the collider energy. This confirms the universal structure of Pomeron exchange. The data at relatively low multiplicities indicate that the size of the source created by one-Pomeron exchange is much less than the size of the proton.
119436494
QCD Interconnection Effects
Heavy objects like the W, Z and t are short-lived compared with typical hadronization times. When pairs of such particles are produced, the subsequent hadronic decay systems may therefore become interconnected. We study such potential effects at Linear Collider 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.
119197298
Uplifting amplitudes in special kinematics
A bstractWe consider scattering amplitudes in planar $ \mathcal{N} $ = 4 supersymmetric Yang-Mills theory in special kinematics where all external four-dimensional momenta are restricted to a (1+1)-dimensional subspace. The amplitudes are known to satisfy non-trivial factorisation properties arising from multi-collinear limits, which we further study here. We are able to find a general solution to these multi-collinear limits. This results in a simple formula which represents an n-point superamplitude in terms of a linear combination of functions Sm which are constrained to vanish in all appropriate multi-collinear limits. These collinear-vanishing building blocks, Sm, are dual-conformally-invariant functions which depend on the reduced m-point kinematics with 8 ≤ m ≤ 4ℓ. For MHV amplitudes they can be constructed directly using, for example, the approach in ref. [1]. This procedure provides a universal uplift of lower-point collinearly vanishing building blocks Sm to all higher-point amplitudes. It works at any loop-level ℓ ≥ 1 and for any MHV or NkMHV amplitude. We compare this with explicit examples involving n-point MHV amplitudes at 2-loops and 10-point MHV amplitudes at 3-loops. Tree-level superamplitudes have different properties and are treated separately from loop-level amplitudes in our approach. To illustrate this we derive an expression for n-point tree-level NMHV amplitudes in special kinematics.
115628770
Valley trajectories in gauge theories
120263136
Higher twist effects in the Drell‐Yan process
We calculate the angular distribution of the lepton produced in the Drell‐Yan reaction taking into account pion bound state effects. We work in the kinematic region where one of the pion constituents goes far off shell, which allows us to treat the bound state problem pertubatively. We show that the angular distribution is very sensitive to the shape of the pion distribution amplitude. The model we discuss fits the data if we choose a two‐humped pion distribution amplitude suggested by QCD sum rules.
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.
119379193
The calculus of many instantons
We describe the modern formalism, ideas and applications of the instanton calculus for gauge theories with, and without, supersymmetry. Particular emphasis is put on developing a formalism that can deal with any number of instantons. This necessitates a thorough review of the ADHM construction of instantons with arbitrary charge and an in-depth analysis of the resulting moduli space of solutions. We review the construction of the ADHM moduli space as a hyper-Kahler quotient. We show how the functional integral in the semi-classical approximation reduces to an integral over the instanton moduli space in each instanton sector and how the resulting matrix partition function involves various geometrical quantities on the instanton moduli space: volume form, connection, curvature, isometries, etc. One important conclusion is that this partition function is the dimensional reduction of a higher- dimensional gauged linear sigma model which naturally leads us to describe the relation of the instanton calculus to D-branes in string theory. Along the way we describe powerful applications of the calculus of many instantons to supersymmetric gauge theories including (i) the gluino condensate puzzle in N = 1 theories (ii) Seiberg-Witten theory in N = 2 theories; and (iii) the AdS/CFT correspondence in N = 2 and N = 4 theories. Finally, we brielfy review the modifications of the instanton calculus for a gauge theory defined on a non-commutative spacetime and we also describe a new method for calculating instanton processes using a form of localization on the instanton moduli space.