455 research outputs found
Quark Transversity Distribution in Perturbative QCD: Light-Front Hamiltonian Approach
To resolve the current ambiguity in the splitting function corresponding to
the quark transversity distribution , we calculate for a
dressed quark in light-front Hamiltonian perturbation theory. Our result agrees
with the expected form of the splitting function found in the literature and
disagrees with the recent calculation in \cite{kuhn}. We emphasize the
importance of quark mass in in perturbative QCD and show its
connection with a part of .Comment: minor changes in the text, references adde
Off-forward Matrix Elements in Light-front Hamiltonian QCD
We investigate the off-forward matrix element of the light cone vector
operator for a dressed quark state in light-front Hamiltonian perturbation
theory. We obtain the corresponding splitting functions in a straightforward
way. We show that the end point singularity is canceled by the contribution
from the normalization of state. Considering mixing with the gluon operator, we
verify the helicity sum rule in perturbation theory. We show that the quark
mass effects are suppressed in the plus component of the matrix element but in
the transverse component, they are not suppressed. We emphasize that this is a
particularity of the off-forward matrix element and is absent in the forward
case.Comment: 12 pages, revtex, 1 figur
A Field Theoretic Investigation of Spin in QCD
Utilizing the kinematical boost in light-front formalism one can address the
issue of relativistic spin operators in an arbitrary reference frame. In the
gauge , the interaction dependent transverse spin operators can be
separated into three parts. In analogy with the helicity sum rule, we propose a
transverse spin sum rule. We perform a one loop renormalization of the
transverse spin operator and show that the counterterm needed is the same as
the linear mass counterterm in the light-front QCD Hamiltonian.Comment: 4 pages, Latex2e, contribution to the proceedings of Tenth
International Light-Cone Meeting on Non-Perturbative QCD and Hadron
Phenomenology, Heidelberg, June 12-17, 200
Twist Three Distribution e(x) : Sum Rules and Equation of Motion Relations
We investigate the twist three distribution function in light-front
Hamiltonian perturbation theory. In light-front gauge, by eliminating the
constrained field, we find a mass term, an intrinsic transverse momentum
dependent term and a 'genuine twist three' quark-gluon interaction term in the
operator. The equation of motion relation, moment relation and the sum rules
are satisfied for a quark at one loop. We compare the results with other model
calculations.Comment: genuine twist three part added, conclusions on sum rules and equation
of motion unchange
Nonperturbative Description of Deep Inelastic Structure Functions in Light-Front QCD
We explore the deep inelastic structure functions of hadrons
nonperturbatively in an inverse power expansion of the light-front energy of
the probe in the framework of light-front QCD. We arrive at the general
expressions for various structure functions as the Fourier transform of matrix
elements of different components of bilocal vector and axial vector currents on
the light-front in a straightforward manner. The complexities of the structure
functions are mainly carried by the multi-parton wave functions of the hadrons,
while, the bilocal currents have a dynamically dependent yet simple structure
on the light-front in this description. We also present a novel analysis of the
power corrections based on light-front power counting which resolves some
ambiguities of the conventional twist analysis in deep inelastic processes.
Further, the factorization theorem and the scale evolution of the structure
functions are presented in this formalism by using old-fashioned light-front
time-ordered perturbation theory with multi-parton wave functions.
Nonperturbative QCD dynamics underlying the structure functions can be explored
in the same framework. Once the nonperturbative multi-parton wave functions are
known from low-energy light-front QCD, a complete description of deep inelastic
structure functions can be realized.Comment: Revtex, 30 pages and no figur
Hadron Optics: Diffraction Patterns in Deeply Virtual Compton Scattering
We show that the Fourier transform of the Deeply Virtual Compton Scattering
(DVCS) amplitude with respect to the skewness variable at fixed
invariant momentum transfer squared provides a unique way to visualize the
structure of the target hadron in the boost-invariant longitudinal coordinate
space. The results are analogous to the diffractive scattering of a wave in
optics. As a specific example, we utilize the quantum fluctuations of a fermion
state at one loop in QED to obtain the behavior of the DVCS amplitude for
electron-photon scattering. We then simulate the wavefunctions for a hadron by
differentiating the above LFWFs with respect to and study the
corresponding DVCS amplitudes in light-front longitudinal space. In both cases
we observe that the diffractive patterns in the longitudinal variable conjugate
to sharpen and the positions of the first minima move in with
increasing momentum transfer. For fixed , higher minima appear at positions
which are integral multiples of the lowest minimum. Both these observations
strongly support the analogy with diffraction in optics.Comment: Some plots modified, clarifications and references adde
On the Matrix Element of the Transverse Component of Bilocal Vector Current and its Parton Interpretation
In this paper we study the matrix element of the transverse component of the
bilocal vector current in the context of deep inelastic scattering. BJL limit
of high energy amplitudes together with light-front current algebra imply the
same parton interpretation for its matrix element as that of the plus
component. On the other hand, the transverse component depends explicitly on
the gluon field operator in QCD, appears as "twist three" and hence its matrix
element has no manifest parton interpretation. In this paper we perform
calculations in light-front time-ordering perturbative QCD for a dressed quark
target to order and demonstrate that the matrix element of the
transverse component of the bilocal vector current has the same parton
interpretation as that of the plus component.Comment: 7 pages, REVTE
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