126284528
MULTIPERIPHERAL QUARK FRAGMENTATION
119081579
Perturbative QCD with quark and gluon condensates
The quark 〈 ψ ¯ ψ 〉 and gluon ( F μν F μν ) vacuum expectation values are non-vanishing at low orders in α s when the perturbative ground state includes quark and gluon pairs. This offers possibilities of studying the effects of a non-trivial vacuum using formally exact perturbative methods. The QCD Feynman rules are modified only for the free, on-shell quark and gluon propagators at zero four-momentum. Gauge and lorentz invariance is maintained, while chiral symmetry is spontaneously broken by the ground state.
120877951
Sister trajectories in the dual resonance model
Abstract The existence of a Regge tranjectory γ = α /3 − 1 in the eight-point amplitude of the Dual Resonance Model set of demonstrated. It is suggested that the three presently known trajectories α, β and γ are part of an infinite set of “sister” trajectories, the expected properties of which are discussed.
121596214
Test of duality in baryon--antibaryon amplitudes from Reggeon--particle scattering
Abstract By studying the backward production data for meson resonances we investigate the dual properties of baryon-Reggeised antibaryon elastic scattering. We find strong support for the duality prediction that meson resonances in the baryon antibaryon channel should be dual to an exotic trajectory.
120890782
Mesons and baryons from QCD
Abstract We study a gauge covariant method for quark bound states in 3 + 1 dimensions, based on a stationary phase approximation of the gluon path integral. Assuming thet lim | x |→∞ F μν a ( x ) F a μν ( x ) ≠ 0 we find meson (q q ) and baryon (qqq) states bound by a Coulomb + linear potential. The quark wave function is confined, as in the bag model. The high-spin states lie on asymptotically linear Regge trajectories of universal slope.
412880
Duality in Semi-Exclusive Processes
Semi-exclusive processes like \gamma p \to \pi^+ Y are closely analogous to DIS, ep \to eX, in the limit where the momentum transfer |t| to the pion and the mass of the inclusive system Y are large but still much smaller than the total CM energy. We apply Bloom-Gilman duality to this semi-exclusive process. The energy dependence of the \gamma p \to \pi^+ n cross section given by semi-local duality agrees with data for moderate values of |t|, but its normalization is underestimated by about two orders of magnitude. This indicates that rather high momentum transfers are required for the validity of PQCD in the hard subprocess \gamma u \to \pi^+ d. In the case of Compton scattering \gamma p \to \gamma p the analogous discrepancy is about one order of magnitude. In electroproduction the virtuality of the incoming photon can be used to directly measure the hardness of the subprocess.
18881983
QCD factorization at fixed Q^2(1-x)
Amplitudes of hard {\it exclusive} processes such as \gamma^*(Q^2) N \to \gamma Y, where Y=N (DVCS) or any other state with a limited mass (M_Y^2 << Q^2), factorize into a hard subprocess amplitude and a target (transition) GPD. The corresponding {\it inclusive} cross section, summed over all states Y of a given (limited) mass, is then given by the discontinuity of a forward multiparton distribution. An application to the Drell-Yan process \pi^+ N \to \gamma^*(x_F,Q^2)+Y allows to explain the observed longitudinal polarization of the virtual photon at high x_F.
119388879
Comments on the Relativity of Shape
In this talk I address three topics related to the shape of hadrons:1. The Lorentz contraction of bound states. Few dedicated studies of this exist — I describe a recent calculation for ordinary atoms (positronium).2. Does the A‐dependence of nuclear structure functions indicate a change of proton shape in the nuclear environment? (My short answer is no.)3. The size of Fock states contributing to processes involving large momentum transfers. End‐point configurations can be transversally extended and yet sufficiently short‐lived to contribute coherently to hard scattering.
118891192
Rescattering Effects on DIS Parton Distributions
Rescattering of the struck quark in Deep Inelastic Scattering implies that measured parton distributions are not directly related to the Fock state probabilities of the target wave function. The production amplitudes acquire dynamical phases, which gives rise to shadowing and diffraction in DIS.
829521
The Unexpected Role of Final State Interactions in Deep Inelastic Scattering
Rescattering of the struck quark in Deep Inelastic Scattering implies that measured parton distributions are not directly related to the Fock state probabilities of the target wave function. The production amplitudes acquire dynamical phases, which gives rise to shadowing and diffraction in DIS. I review the kinematics and dynamics of DIS as seen in various frames and gauges.
119248859
Measuring Transverse Size with Virtual Photons
Fourier transforming the virtual photon transverse momentum in γ(q⊥) + N → f processes allows new insight into hadron dynamics as a function of impact parameter b. I discuss how previous analyses of charge density based on elastic and transition form factors (f = N,N∗) can be generalized to any multi-hadron final state (f = πN, ππN, D̄Λc, . . .). The b-distribution determines the transverse positions of the quarks that the photon couples to, and can be studied as a function of multiplicity, the relative transverse momenta, quark masses and polarization. The method requires no factorization nor leading twist approximation. Data with spacelike photon virtualities in the range 0 ≤ Q ≤ Qmax provides a resolution ∆b & 1/Qmax in impact parameter. ∗Talk at the Third International Workshop on Transverse Polarization Phenomena in Hard Scattering (Transversity 2011), in Veli Los̆inj, Croatia, 29 August 2 September 2011. ar X iv :1 11 0. 33 93 v1 [ he pph ] 1 5 O ct 2 01 1 1. Charge density from elastic form factors The quark density of a hadron in transverse (impact parameter) space b is given by a twodimensional Fourier transform of the electromagnetic form factor of the hadron [1, 2, 3, 4]. For a proton with helicity λ the density distribution is ρq/N (b) ≡ ∫ dq⊥ (2π)2 e−i q⊥·b 1 2P+ 〈P, 1 2q⊥, λ| j (0) |P+,−2q⊥, λ〉