The structure of the matrix elements of the energy-momentum tensor play an important role in determining the properties of the form factors A(q 2 ), B(q 2 ) and C(q 2 ) which appear in the Lorentz covariant decomposition of the matrix elements. In this paper we apply a rigorous frameindependent distributional-matching approach to the matrix elements of the Poincaré generators in order to derive constraints on these form factors as q → 0. In contrast to the literature, we explicitly demonstrate that the vanishing of the anomalous gravitomagnetic moment B(0) and the condition A(0) = 1 are independent of one another, and that these constraints are not related to the specific properties or conservation of the individual Poincaré generators themselves, but are in fact a consequence of the physical on-shell requirement of the states in the matrix elements and the manner in which these states transform under Poincaré transformations. *

We prove the Lorentz invariance of the angular momentum conservation law and the helicity sum rule for relativistic composite systems in the lightfront formulation. We explicitly show that j 3 , the z-component of the angular momentum remains unchanged under Lorentz transformations generated by the light-front kinematical boost operators. The invariance of j 3 under Lorentz transformations is a feature unique to the front form. Applying the Lorentz invariance of the angular quantum number in the front form, we obtain a selection rule for the orbital angular momentum which can be used to eliminate certain interaction vertices in QED and QCD. We also generalize the selection rule to any renormalizable theory and show that there exists an upper bound on the change of orbital angular momentum in scattering processes at any fixed order in perturbation theory.

We evaluate the frame-independent gluon and charm parton-distribution functions (PDFs) of the deuteron utilizing light-front quantization and the impulse approximation. We use a nuclear wave function obtained from solving the nonrelativistic Schrödinger equation with the realistic Argonne v18 nuclear force, which we fold with the proton PDF. The predicted gluon distribution in the deuteron (per nucleon) is a few percent smaller than that of the proton in the domain x b j = Q 2 2p N ·q ∼ 0.4, whereas it is strongly enhanced for x b j larger than 0.6. We discuss the applicability of our analysis and comment on how to extend it to the kinematic limit x b j → 2. We also analyze the charm distribution of the deuteron within the same approach by considering both the perturbatively and non-perturbatively generated (intrinsic) charm contributions. In particular, we note that the intrinsic-charm content in the deuteron will be enhanced due to 6-quark "hidden-color" QCD configurations.