7708439
Dressing the Quark with QCD Condensates
A condensate of $\pvec = 0$ partons in the perturbative vacuum gives rise to a term $\propto\delta^4(p)$ in the free PQCD propagators. The leading condensate contribution to the quark propagator can be exactly summed since there is a factor $\delta^4(p)$ associated to each loop. We calculate the dressed quark propagator in the presence of either a gluon or a quark condensate, for a number of colors $N \to \infty$. The dressed quark propagator satisfies a Dyson-Schwinger type equation which can be exactly solved within our framework. In the case of a gluon condensate the dressed quark propagator has no pole, hence quarks cannot appear in asymptotic states, and moreover the DS equation has a solution which spontaneously breaks chiral symmetry. We also calculate the dressed quark-photon vertex and verify that the corresponding Ward-Takahashi identity is satisfied, and that the dressed self-energy correction to the photon propagator does not shift the physical photon pole.
125593487
NEW DUALITY CONSTRAINTS ON MESON AMPLITUDES
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.
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.
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.
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〉
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.
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.
119327590
Semi-exclusive DVCS
We consider Semi-Exclusive Deeply Virtual Compton Scattering, gamma* p \to gamma Y (SECS), where Y is an inclusive state of intermediate mass, \Lambda_QCD<<m_Y<<Q. When the photon is produced with a large transverse momentum k_T \sim m_Y the subprocess is hard and the struck quark fragments independently of the target spectators. Using completeness this allows to express the SECS cross section in terms of ordinary parton distributions. Apart from direct comparisons with data (yet to come) new information on Bloom-Gilman duality may be obtained through comparisons of resonance production via DVCS (gamma* p \to gamma N*) with the SECS scaling distribution in m_Y.
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.