7 research outputs found
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
Non-linear feedback effects in coupled Boson-Fermion systems
We address ourselves to a class of systems composed of two coupled subsystems
without any intra-subsystem interaction: itinerant Fermions and localized
Bosons on a lattice. Switching on an interaction between the two subsystems
leads to feedback effects which result in a rich dynamical structure in both of
them. Such feedback features are studied on the basis of the flow equation
technique - an infinite series of infinitesimal unitary transformations - which
leads to a gradual elimination of the inter-subsystem interaction. As a result
the two subsystems get decoupled but their renormalized kinetic energies become
mutually dependent on each other. Choosing for the inter - subsystem
interaction a charge exchange term (the Boson-Fermion model) the initially
localized Bosons acquire itinerancy through their dependence on the
renormalized Fermion dispersion. This latter evolves from a free particle
dispersion into one showing a pseudogap structure near the chemical potential.
Upon lowering the temperature both subsystems simultaneously enter a
macroscopic coherent quantum state. The Bosons become superfluid, exhibiting a
soundwave like dispersion while the Fermions develop a true gap in their
dispersion. The essential physical features described by this technique are
already contained in the renormalization of the kinetic terms in the respective
Hamiltonians of the two subsystems. The extra interaction terms resulting in
the process of iteration only strengthen this physics. We compare the results
with previous calculations based on selfconsistent perturbative approaches.Comment: 14 pages, 16 figures, accepted for publication in Phys. Rev.
Renormalization of Hamiltonian Field Theory; a non-perturbative and non-unitarity approach
Renormalization of Hamiltonian field theory is usually a rather painful
algebraic or numerical exercise. By combining a method based on the coupled
cluster method, analysed in detail by Suzuki and Okamoto, with a Wilsonian
approach to renormalization, we show that a powerful and elegant method exist
to solve such problems. The method is in principle non-perturbative, and is not
necessarily unitary.Comment: 16 pages, version shortened and improved, references added. To appear
in JHE
Twist Four Longitudinal Structure Function in Light-Front QCD
To resolve various outstanding issues associated with the twist four
longitudinal structure function we perform an analysis
based on the BJL expansion for the forward virtual photon-hadron Compton
scattering amplitude and equal (light-front) time current algebra. Using the
Fock space expansion for states and operators, we evaluate the twist four
longitudinal structure function for dressed quark and gluon targets in
perturbation theory. With the help of a new sum rule which we have derived
recently we show that the quadratic and logarithmic divergences generated in
the bare theory are related to corresponding mass shifts in old-fashioned
light-front perturbation theory. We present numerical results for the and
structure functions for the meson in two-dimensional QCD in the one pair
approximation. We discuss the relevance of our results for the problem of the
partitioning of hadron mass in QCD.Comment: 25 pages, 2 ps figures, accepted for publication in Physical Review
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The Drell-Hearn-Gerasimov sum-rule at polarized HERA
The Drell-Hearn-Gerasimov sum-rule for spin dependent photoproduction relates the difference of the two cross-sections for the absorption of a real photon with spin anti-parallel {sigma}{sub A} and parallel {sigma}{sub P} to the target spin to the square of the anomalous magnetic moment of the target nucleon. The authors discuss the potential of polarized HERA to measure the spin dependent part of the total photoproduction cross section at large {radical}(s{sub {gamma}p})