122002771
On spin-parity determination of X0 (960) meson in the electromagnetic production processes
Abstract The processes of the X 0 (960) electromagnetic production (photoproduction on helium and proton, in e + e − pair annihilation, etc.) as well as the X 0 (960) radiation decays (X 0 → ϱ e + e − , X 0 → ϱγ with polarized photons) are analyzed in detail with the purpose of determining the X 0 (960) spin. Experiments, allowing the distinction of J P =2 − and 0 − hypotheses for X 0 (960) spin-parity, are suggested.
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.
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.
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.
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.
16588286
Recursion relations for gauge theory amplitudes with massive vector bosons and fermions
We apply the on-shell tree-level recursion relations of Britto, Cachazo, Feng and Witten to a variety of processes involving internal and external massive particles with spin. We show how to construct multi-vector boson currents where one or more off-shell vector bosons couples to a quark pair and number of gluons. We give compact results for single vector boson currents with up to six partons and double vector boson currents with up to four partons for all helicity combinations. We also provide expressions for single vector boson currents with a quark pair and an arbitrary number of gluons for some specific helicity configurations. Finally, we show how to generalise the recursion relations to handle massive particles with spin on internal lines using gg→t as an example.
12975212
GAUGE THEORY AMPLITUDES, SCALAR GRAPHS AND TWISTOR SPACE
We discuss a remarkable new approach initiated by Cachazo, Svrcek and Witten for calculating gauge theory amplitudes. The formalism amounts to an effective scalar perturbation theory which in many cases offers a much simpler alternative to the usual Feynman diagrams for deriving n-point amplitudes in gauge theory. At tree level the formalism works in a generic gauge theory, with or without supersymmetry, and for a finite number of colours. There is also a growing evidence that the formalism works for loop amplitudes.
16015460
New tests of the pp-wave correspondence
The pp-wave/SYM correspondence is an equivalence relation, H string = ??J , between the hamiltonian H string of string field theory in the pp-wave background and the dilatation operator ? in = 4 Super Yang-Mills in the double scaling limit. We calculate matrix elements of these operators in string field theory and in gauge theory. In the string theory Hilbert space we use the natural string basis, and in the gauge theory we use the basis which is isomorphic to it. States in this basis are specific linear combinations of the original BMN operators, and were constructed previously for the case of two scalar impurities. We extend this construction to incorporate BMN operators with vector and mixed impurities. This enables us to verify from the gauge theory perspective two key properties of the three-string interaction vertex of Spradlin and Volovich: (1) the vanishing of the three-string amplitude for string states with one vector and one scalar impurity; and (2) the relative minus sign in the string amplitude involving states with two vector impurities compared to that with two scalar impurities. This implies a spontaneous breaking of the 2 symmetry of the string field theory in the pp-wave background. Furthermore, we calculate the gauge theory matrix elements of ??J for states with an arbitrary number of scalar impurities. In all cases we find perfect agreement with the corresponding string amplitudes derived from the three-string vertex.
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.