44 research outputs found
The Parton Model and its Applications
This is a review of the program we started in 1968 to understand and
generalize Bjorken scaling and Feynman's parton model in a canonical quantum
field theory. It is shown that the parton model proposed for deep inelastic
electron scatterings can be derived if a transverse momentum cutoff is imposed
on all particles in the theory so that the impulse approximation holds. The
deep inelastic electron-positron annihilation into a nucleon plus anything else
is related by the crossing symmetry of quantum field theory to the deep
inelastic electron-nucleon scattering. We have investigated the implication of
crossing symmetry and found that the structure functions satisfy a scaling
behavior analogous to the Bjorken limit for deep inelastic electron scattering.
We then find that massive lepton pair production in collisions of two high
energy hadrons can be treated by the parton model with an interesting scaling
behavior for the differential cross sections. This turns out to be the first
example of a class of hard processes involving two initial hadrons.Comment: Contribution to a book to be published by World Scientific for the
occasion of 50 Years of Quarks. 17 pages, 4 figure
Comment on "Light-front Schwinger model at finite temperature"
In a recent paper by A. Das and X. Zhou [Phys. Rev. D 68, 065017 (2003)] it
is claimed that explicit evaluation of the thermal photon self-energy in the
Schwinger model gives off-shell thermal Green functions that are different in
light-front and conventional quantizations. We show that the claimed difference
originates from an erroneous simplification of the fermion propagator used in
the light-front calculation.Comment: 8 pages, revtex4, added section refuting the massless limit proposed
in hep-th/031102
Self Consistent Expansion In The Presence Of Electroweak Interactions
In the conventional approach to the expansion, electroweak
interactions are switched off and large QCD is treated in isolation. We
study the self-consistency of taking the large limit in the presence of
electroweak interaction. If the electroweak coupling constants are held
constant, the large counting rules are violated by processes involving
internal photon or weak boson lines. Anomaly cancellations, however, fix the
ratio of electric charges of different fermions. This allows a self-consistent
way to scale down the electronic charge in the large limit and hence
restoring the validity of the large counting rules.Comment: 9 pages in REVTeX, no figure
CKM Favored Semileptonic Decays of Heavy Hadrons at Zero Recoil
We study the properties of Cabibbo-Kobayashi-Maskawa (CKM) favored
semileptonic decays of mesons and baryons containing a heavy quark at the point
of no recoil. We first use a diagrammatic analysis to rederive the result
observed by earlier authors that at this kinematic point the meson decays
via transitions can only produce a or meson. The result is
generalized to include photon emissions which violate heavy quark flavor
symmetry. We show that photons emitted by the heavy quarks and the charged
lepton are the only light particles that can decorate the decays at zero recoil, and the similar processes of heavy baryons.
Implications for the determinations of the CKM parameter are
discussed. Also studied in this paper is the connection between our
diagrammatic analysis of suppression of particle emission and the formal
observation based on weak currents at zero recoil being generators of heavy
quark symmetry. We show that the two approaches can be unified by considering
the Isgur-Wise function in the presence of an external source.Comment: 27 pages, including 11 figures using macros FEYNMAN.te