Dae Sung Hwang

Light-Cone Wavefunction Representation of Deeply Virtual Compton Scattering

Abstract We give a complete representation of virtual Compton scattering γ ∗ p→γp at large initial photon virtuality Q 2 and small momentum transfer squared t in terms of the light-cone wavefunctions of the target proton. We verify the identities between the skewed parton distributions H(x,ζ,t) and E(x,ζ,t) which appear in deeply virtual Compton scattering and the corresponding integrands of the Dirac and Pauli form factors F 1 (t) and F 2 (t) and the gravitational form factors A q (t) and B q (t) for each quark and anti-quark constituent. We illustrate the general formalism for the case of deeply virtual Compton scattering on the quantum fluctuations of a fermion in quantum electrodynamics at one loop.

Light cone representation of the spin and orbital angular momentum of relativistic composite systems

Abstract The matrix elements of local operators such as the electromagnetic current, the energy–momentum tensor, angular momentum, and the moments of structure functions have exact representations in terms of light-cone Fock state wavefunctions of bound states such as hadrons. We illustrate all of these properties by giving explicit light-cone wavefunctions for the two-particle Fock state of the electron in QED, thus connecting the Schwinger anomalous magnetic moment to the spin and orbital angular momentum carried by its Fock state constituents. We also compute the QED one-loop radiative corrections for the form factors for the graviton coupling to the electron and photon. Although the underlying model is derived from elementary QED perturbative couplings, it in fact can be used to simulate much more general bound state systems by applying spectral integration over the constituent masses while preserving all of the Lorentz properties, giving explicit realization of the spin sum rules and other local matrix elements. The role of orbital angular momentum in understanding the “spin crisis” problem for relativistic systems is clarified. We also prove that the anomalous gravitomagnetic moment B(0) vanishes for any composite system. This property is shown to follow directly from the Lorentz boost properties of the light-cone Fock representation and holds separately for each Fock state component. We show how the QED perturbative structure can be used to model bound state systems while preserving all Lorentz properties. We thus obtain a theoretical laboratory to test the consistency of formulae which have been proposed to probe the spin structure of hadrons.

Initial-State Interactions in the Unpolarized Drell-Yan Process

We show that initial-state interactions contribute to the cos 2phi distribution in unpolarized Drell-Yan lepton pair production pp and p (p) over bar-->l(+)l(-)X, without suppression. The asymmetry is expressed as a product of chiral-odd distributions h(1)(perpendicular to)(x(1),p(perpendicular to)(2))x (h) over bar (perpendicular to)(1)(x(2),k(perpendicular to)(2)), where the quark-transversity function h(1)(perpendicular to)(x,p(perpendicular to)(2)) is the transverse momentum dependent, light-cone momentum distribution of transversely polarized quarks in an unpolarized proton. We compute this (naive) T-odd and chiral-odd distribution function and the resulting cos 2phi asymmetry explicitly in a quark-scalar diquark model for the proton with initial-state gluon interaction. In this model the function h(1)(perpendicular to)(x,p(perpendicular to)(2)) equals the T-odd (chiral-even) Sivers effect function f(1T)(perpendicular to)(x,p(perpendicular to)(2)). This suggests that the single-spin asymmetries in the semi-inclusive deep inelastic scattering and the Drell-Yan process are closely related to the cos 2phi asymmetry of the unpolarized Drell-Yan process, since all can arise from the same underlying mechanism. This provides new insight regarding the role of the quark and gluon orbital angular momentum as well as that of initial- and final-state gluon exchange interactions in hard QCD processes.

Disentangling Higgs-top couplings in associated production

A bstractIn the presence of CP violation, the Higgs-top coupling may have both scalar and pseudoscalar components, κt and

Exact Light-Cone Wavefunction Representation of Matrix Elements of Electroweak Currents ∗

{{\widetilde{\kappa}}_t}

A fast track towards the 'Higgs' spin and parity

, which are bounded indirectly but only weakly by the present experimental constraints on the Higgs-gluon-gluon and Higgs-γ-γ couplings, whereas upper limits on electric dipole moments provide strong additional indirect constraints on

Sivers asymmetry and generalized parton distributions in impact parameter space

{{\widetilde{\kappa}}_t}

Single-Spin Polarization Effects and the Determination of Timelike Proton Form Factors

, if the Higgs-electron coupling is similar to that in the Standard Model and there are no cancellations with other contributions. We discuss methods to measure directly the scalar and pseudoscalar Higgs-top couplings by measurements of Higgs production in association with

Final-State Interactions and Single-Spin Asymmetries in Semi-inclusive Deep Inelastic Scattering

\overline{t}t

The Covariant structure of light front wave functions and the behavior of hadronic form-factors

, single t and single