Rajen Kundu

Orbital angular momentum in deep inelastic scattering

In this work we address several issues associated with the orbital angular momentum relevant for leading twist polarized deep inelastic scattering. We present a detailed analysis of the light-front helicity operator (generator of rotations in the transverse plane) in QCD. We explicitly show that the operator constructed from the manifestly gauge invariant, symmetric energy momentum tensor in QCD, in the gauge

Deep inelastic structure functions in light-front QCD: Radiative corrections

{A}^{+}=0,

On transverse spin sum rules

after the elimination of constraint variables, is equal to the naive canonical form of the light-front helicity operator plus surface terms. Restricting to the topologically trivial sector, we eliminate the residual gauge degrees of freedom and surface terms. Having constructed the gauge fixed light-front helicity operator, we introduce quark and gluon orbital helicity distribution functions relevant for polarized deep inelastic scattering as a Fourier transform of the forward hadron matrix elements of appropriate bilocal operators. The utility of these definitions is illustrated with the calculation of anomalous dimensions in perturbation theory. We explicitly verify the helicity sum rule for dressed quark and gluon targets in light-front perturbation theory. We also consider the internal orbital helicity of a composite system in an arbitrary reference frame and contrast the results in the nonrelativistic situation versus the light-front (relativistic) case.

Nonperturbative Description of Deep Inelastic Structure Functions in Light-Front QCD

Recently, we have introduced a unified theory to deal with perturbative and non-perturbative QCD contributions to hadronic structure functions in deep inelastic scattering. This formulation is realized by combining the coordinate space approach based on light-front current algebra techniques and the momentum space approach based on Fock space expansion methods in the Hamiltonian formalism of light-front field theory. In this work we show how a perturbative analysis in the light-front Hamiltonian formalism leads to the factorization scheme we have proposed recently. The analysis also shows that the scaling violations due to perturbative QCD corrections can be rather easily addressed in this framework by simply replacing the hadron target by dressed parton target and then carrying out a systematic expansion in the coupling constant

A numerical experiment in DLCQ: microcausality, continuum limit and all that

\alpha_s

Sum rule for the twist four longitudinal structure function

based on the perturbative QCD expansion of the dressed parton target. The tools employed for this calculation are those available from light-front old-fashioned perturbation theory. We present the complete set of calculations of unpolarized and polarized deep inelastic structure functions to order

Twist four longitudinal structure function in light front QCD

\alpha_s

Utility of Galilean Symmetry in Light-Front Perturbation Theory: A Nontrivial Example in QCD

. We extract the relevant splitting functions in all the cases. We explicitly verify all the sum rules to order

Comment on "Proton spin structure from measurable parton distributions".

\alpha_s

Hamiltonian analysis of the deep inelastic structure function

. We demonstrate the validity of approximations made in the derivation of the new factorization scheme. This is achieved with the help of detailed calculations of the evolution of structure function of a composite system carried out using multi-parton wavefunctions.