119248867
Central exclusive meson pair production in the perturbative regime at hadron colliders
The central exclusive production (CEP) of heavy resonance states that subsequently decay into meson pairs, $M\overline{M}$, is an important signature for such processes at hadron colliders. However, there is a potentially important background from the direct QCD production of meson pairs, as mediated for example by the exclusive $gg\to M\overline{M}$ hard scattering subprocess. This is in fact an interesting process in its own right, testing novel aspects of perturbative QCD technology. We explicitly calculate the $gg \to M\overline{M}$ helicity amplitudes for different meson states within the hard exclusive formalism, and comment on the application of MHV techniques to the calculation. Using these results, we describe how meson pair CEP can be calculated in the perturbative regime, and present some sample numerical predictions for a variety of final states. We also briefly consider the dominant non-perturbative contributions, which are expected to be important when the meson transverse momentum is small.
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.
125850380
Multiple Hadron Production in Parton {QCD} Jets
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.
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.
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.
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.
15213237
Collinear limits in QCD from MHV rules
We consider multi-parton collinear limits of QCD amplitudes at tree level. Using the MHV formalism we specify the underlying analytic structure of the resulting multi-collinear splitting functions. We derive general results for these splitting functions that are valid for specific numbers of negative helicity partons and an arbitrary number of positive helicity partons (or vice versa).
17672320
Wilsonian effective actions and the IR/UV mixing in noncommutative gauge theories
Using background field perturbation theory we study wilsonian effective actions of noncommutative gauge theories with an arbitrary matter content. We determine the wilsonian coupling constant and the gauge boson polarization tensor as functions of the momentum scale k at the one-loop level and study their short-distance behaviour as θ k→0, where θ is the noncommutativity parameter. The mixing between the short-distance and the long-distance degrees of freedom characteristic of noncommutative field theories violates the universality of the wilsonian action and leads to IR-singularities. We find, in agreement with known results, that the quadratic IR divergences cancel in supersymmetric gauge theories. The logarithmic divergences disappear in mass-deformed = 4 theories, but not in other finite = 2 theories. We next concentrate on finite = 2 and mass-deformed = 4 supersymmetric U(1) gauge theories with massive hypermultiplets. The wilsonian running coupling exhibits a non-trivial threshold behaviour at and well below the noncommutativity scale 1/√θ, eventually becoming flat in the extreme infrared in = 4 theories, but not in = 2 theories. This is interpreted as the (non)-existence of a non-singular commutative limit where the theory is described by a commutative = 2 pure U(1) theory. We expect that our analysis of finite theories is exact to all orders in perturbation theory.
120078928
Non-perturbative contribution to total cross sections in non-abelian gauge theories
Abstract We consider the instanton-induced contribution to the total cross section of vector boson scattering in the SU (2) gauge theory with and without Higgs mechanism. The exponential suppression of instanton-induced processes disappears asymptotically at energies for above the infrared cutoff for the instanton scale size, which is provided, in the Higgs (confinement) phase, by the vacuum expectation value (virtuality of the gluons). Instanton-induced processes may therefore be important in close-to-mass-shell gluon collisions. Our finding also suggests that electroweak baryon-and lepton-number violation with the associated production of many W-bosons may become important at very high energies.
7657370
On Affleck-Dine-Seiberg superpotential and magnetic monopoles in supersymmetric QCD
Certain exact results in supersymmetric gauge theories are generated by non-perturbative effects different from instantons. In supersymmetric QCD with N colours and NF fundamental flavours we examine the Affleck-Dine-Seiberg (ADS) superpotential using controlled semi-classical analysis. We show how for NF< N ? 1 the ADS superpotential arises from monopole contributions to the path integral of the supersymmetric gauge theory compactified on 3 ? S1. These are the monopole effects leading to gaugino condensation and confinement of the low-energy SU(N?NF) supersymmetric gauge theory.