454 research outputs found
Light-Cone Distribution Amplitudes for the Light Mesons
We present a study of light-cone distribution amplitudes of the light
mesons. The first few Gegenbauer moments of leading twist light-cone
distribution amplitudes are calculated by using the QCD sum rule technique.Comment: 18 pages, 9 figures, v3: a sentence revised in the introduction, to
appear in JHE
Asymptotic Pad\'e Approximants and the SQCD -function
We present a prediction for the four loop -function for SQCD based on
the method of Asymptotic Pad\'e Approximants.Comment: 8 pages, including 2 figures. Plain TeX. Uses Harvmac and eps
Model-independent study of the QCD sum rule for the pi NN coupling constant
We reinvestigate the QCD sum rule for the pi NN coupling constant, g,
starting from the vacuum-to-pion matrix element of the correlation function of
the interpolating fields of two nucleons. We study in detail the physical
content of the correlation function without referring to the effective theory.
We consider the invariant correlation functions by splitting the correlation
function into different Dirac structures. We show that the coefficients of the
double-pole terms are proportional to g but that the coefficients of the
single-pole terms are not determined by g. In the chiral limit the single-pole
terms as well as the continuum terms are ill defined in the dispersion
integral. Therefore, the use of naive QCD sum rules obtained from the invariant
correlation functions is not justified. A possible procedure to avoid this
difficulty is discussed.Comment: 20 pages, 2 figure
Qualitative solution of QCD sum rules
We show how such important features of QCD as chiral symmetry breaking or the
formation of a mass-gap can be directly traced from QCD sum rules for two point
functions assuming, in the large number of colors limit, exact duality between
the operator product expansion and the spectrum described by linearly (or
nearly linear) rising Regge trajectories as predicted by string theory. We see
how the presence of chiral symmetry breaking is intimately related to
confinement in this scenario, as expected from general arguments, and how Regge
trajectories change when chiral symmetry is broken. As a result the whole meson
mass spectrum can be parametrized with a good accuracy by the constant
only, thus realizing the program proposed by Migdal some time ago.Comment: Version published in JHE
Cecotti-Fendley-Intriligator-Vafa Index in a Box
The Cecotti-Fendley-Intriligator-Vafa (CFIV) index in two-dimensional
models is revisited. We address the problem of
"elementary" (nontopological) excitations over a kink solution, in the one-kink
sector (using the Wess-Zumino or Landau-Ginzburg models with two vacua as
examples). In other words, we limit ourselves to the large- limit. The
excitation spectrum over the BPS-saturated at the classical level kink is
discretized through a large box with judiciously chosen boundary conditions.
The boundary conditions are designed in such a way that half of supersymmetry
is preserved as well as the BPS kink itself, and relevant zero modes. The
excitation spectrum acquires a mass gap. All (discretized) excited states enter
in four-dimensional multiplets (two bosonic states + two fermionic). Their
contribution to vanishes level by level. The ground
state contribution produces
1/N_c and 1/n preasymptotic corrections to Current-Current correlators
We obtain the corrections in and in ( is the principal
quantum number of the bound state) of the decay constants of scalar and
pseudoscalar currents in two and four dimensions in the large . We obtain
them from the operator product expansion provided a model for the large
mass spectrum is given. In the two-dimensional case the spectrum is known and
the corrections obtained in this paper are model independent. We confirm these
results by confronting them with the numerical solution of the 't Hooft model.
We also consider a model at finite and obtain the associated decay
constants that are consistent with perturbation theory. This example shows that
that the inclusion of perturbative corrections, or finite effects, to the
OPE does not constrain the slope of the Regge trajectories, which remain a free
parameter for each different channel.Comment: 29 pages, 11 figures. Two references adde
Charged particles in external fields as physical examples of quasi-exactly solvable models: a unified treatment
We present a unified treatment of three cases of quasi-exactly solvable
problems, namely, charged particle moving in Coulomb and magnetic fields, for
both the Schr\"odinger and the Klein-Gordon case, and the relative motion of
two charged particles in an external oscillator potential. We show that all
these cases are reducible to the same basic equation, which is quasi-exactly
solvable owing to the existence of a hidden algebraic structure. A
systematic and unified algebraic solution to the basic equation using the
method of factorization is given. Analytic expressions of the energies and the
allowed frequencies for the three cases are given in terms of the roots of one
and the same set of Bethe ansatz equations.Comment: RevTex, 15 pages, no figure
Next--to--Leading Order Corrections to Meson Masses in the Heavy Quark Effective Theory
We use the QCD sum rule approach to calculate the splitting between vector
and pseudoscalar mesons containing one light and one heavy quark, and the
kinetic energy of the heavy quark. Our result for the splitting induced by the
chromomagnetic interaction agrees to the experimental data on charm and beauty
mesons. For the matrix element of the kinetic energy operator, we obtain the
value .Comment: 33 ps., PS figures included, requires REVTEX.3 and psfig,
TUM-T31-42/93/R (additional contribution to kinetic energy taken into
account, marginal changes in the results
N=2 Supersymmetric Kinks and real algebraic curves
The kinks of the (1+1)-dimensional Wess-Zumino model with polynomic
superpotential are investigated and shown to be related to real algebraic
curves.Comment: 8 pages, LaTeX, epsfig, 4 figures include
Non-perturbative Power Corrections to Ghost and Gluon Propagators
We study the dominant non-perturbative power corrections to the ghost and
gluon propagators in Landau gauge pure Yang-Mills theory using OPE and lattice
simulations. The leading order Wilson coefficients are proven to be the same
for both propagators. The ratio of the ghost and gluon propagators is thus free
from this dominant power correction. Indeed, a purely perturbative fit of this
ratio gives smaller value (MeV) of \Lambda_{\ms} than the one
obtained from the propagators separately(MeV). This argues in
favour of significant non-perturbative power corrections in the
ghost and gluon propagators. We check the self-consistency of the method.Comment: 14 pages, 4 figures; replaced with revised version, to appear in JHE
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