211 research outputs found
Analytical Heavy Quark Expansion in the 't Hooft Model
We present a number of exact relations for the heavy quark limit and develop
an analytical 1/m_Q expansion for heavy mesons in the 't Hooft model. Among the
new results are relation 3\mu_\pi^2=\bar\Lambda^2 - m_{sp}^2+\beta^2, 1/m_Q
corrections to the decay constants, to the kinetic expectation values and
1/m_Q^2 nonperturbative corrections to the B->D amplitude at zero recoil. The
properties of the IW functions are addressed and the small velocity sum rules
are verified.Comment: 22 pages, plain LaTeX (no figures
Decoupling of Zero-Modes and Covariance in the Light-Front Formulation of Supersymmetric Theories
We show under suitable assumptions that zero-modes decouple from the dynamics
of non-zero modes in the light-front formulation of some supersymmetric field
theories. The implications for Lorentz invariance are discussed.Comment: 8 pages, revtex, 3 figure
Comparison of quantum field perturbation theory for the light front with the theory in lorentz coordinates
The relationship between the perturbation theory in light-front coordinates
and Lorentz-covariant perturbation theory is investigated. A method for finding
the difference between separate terms of the corresponding series without their
explicit evaluation is proposed. A procedure of constructing additional
counter-terms to the canonical Hamiltonian that compensate this difference at
any finite order is proposed. For the Yukawa model, the light-front Hamiltonian
with all of these counter-terms is obtained in a closed form. Possible
application of this approach to gauge theories is discussed.Comment: LaTex 2.09, 20 pages, 5 figure
Precision Studies of Duality in the 't Hooft Model
We address numerical aspects of local quark-hadron duality using the example
of the exactly solvable 't Hooft model, two-dimensional QCD with N_c -->
infinity. The primary focus of these studies is total semileptonic decay widths
relevant for extracting |V_{cb}| and |V_{ub}|. We compare the exact
channel-by-channel sum of exclusive modes to the corresponding rates obtained
in the standard 1/m_Q expansion arising from the Operator Product Expansion. An
impressive agreement sets in unexpectedly early, immediately after the
threshold for the first hadronic excitation in the final state. Yet even at
higher energy release it is possible to discern the seeds of duality-violating
oscillations. We find the ``Small Velocity'' sum rules to be exceptionally well
saturated already by the first excited state. We also obtain a convincing
degree of duality in the differential distributions and in an analogue of
R_{e^+e^-}(s). Finally, we discuss possible lessons for semileptonic decays of
actual heavy quarks in QCD.Comment: 45 pages, 16 eps figures include
Vacuum Expectation Value of a Wegner-Wilson Loop near the Light Cone
Vacuum expectation values for one Wegner-Wilson loop representing a moving
quark-antiquark pair are calculated in four-dimensional Euclidean and Minkowski
space-time. The calculation uses gluon field strength correlators with
perturbative gluon exchange and non-perturbative correlations from the
stochastic vacuum model. The expectation value of a Wegner-Wilson loop forming
a hyperbolic angle in Minkowski space-time is connected by an analytical
continuation to the expectation value of the Wegner-Wilson loop in Euclidean
four-space. The obtained result shows how confinement enters into the
light-cone Hamiltonian for valence quarks independently of the chosen model.Comment: 12 pages, 2 figures, sections 2 and 3 shortened, more details added
in section
Counting Rule for Hadronic Light-Cone Wave Functions
We introduce a systematic way to write down the Fock components of a hadronic
light-cone wave function with partons and orbital angular momentum
projection . We show that the wave function amplitude
has a leading behavior
when all parton transverse
momenta are uniformly large, where and are the number of partons
and orbital angular momentum projection, respectively, of an amplitude that
mixes under renormalization. The result can be used as a constraint in modeling
the hadronic light-cone wave functions. We also derive a generalized counting
rule for hard exclusive processes involving parton orbital angular momentum and
hadron helicity flip.Comment: 7 pages, no figur
NAMBU-GOLDSTONE BOSON ON THE LIGHT-FRONT
Spontaneous breakdown of the continuous symmetry is studied in the framework
of discretized light-front quantization. We consider linear sigma model in 3+1
dimensions and show that the careful treatment of zero modes together with the
regularization of the theory by introducing NG boson mass leads to the correct
description of Nambu-Goldstone phase on the light-front.Comment: To appear in the proceedings of the 13th Symposium on Theoretical
Physics, Mt. Sorak, Korea, from 27 June to 2 July, 1994
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