38 research outputs found
A model calculation of the value of the electromagnetic coupling constant at
A QCD model with an infinite number of vector mesons suggested by one of the
authors is used to derive the value of the correction for
due to the strong interactions. The result is
; thus .Comment: in LaTeX, 6 pages, 0 figures, ITEP Preprint 49-9
Constraints on the nonuniversal Z^\prime couplings from B\to\pi K, \pi K^{\ast} and \rho K Decays
Motivated by the large difference between the direct CP asymmetries
and , we
combine the up-to-date experimental information on ,
and decays to pursue possible solutions with the nonuniversal
model. Detailed analyses of the relative impacts of different
types of couplings are presented in four specific cases. Numerically, we find
that the new coupling parameters, and with a common
nontrivial new weak phase , which are relevant to the
contributions to the electroweak penguin sector
and , are crucial to the observed " puzzle". Furthermore,
they are found to be definitely unequal and opposite in sign. We also find that
can put a strong constraint on the new
couplings, which implies the contributions to the coefficient of
QCD penguins operator involving the parameter required.Comment: 27 pages, 6 figures. References and a note adde
Radiative corrections to hard spectator scattering in decays
We present the calculation of the next-to-leading corrections to the tree
amplitudes which appear in the description of non-leptonic B-decays in the
factorization approach. These corrections, together with radiative corrections
to the jet functions, represent the full next-to-leading contributions to the
dominant hard spectator scattering term generated by operators in the
decay amplitudes. Using obtained analytical results we estimate
branchings fractions in the physical (or BBNS) factorization scheme. We have
also found that the imaginary part generated in the hard spectator scattering
term is rather large compared to the imaginary part of the vertex contribution.Comment: text is improved and typos are corrected, accepted for publication in
JHE
Hadronic decay, the renormalization group, analiticity of the polarization operators and QCD parameters
The ALEPH data on hadronic tau-decay is throughly analysed in the framework
of QCD. The perturbative calculations are performed in 1-4-loop approximation.
The analytical properties of the polarization operators are used in the whole
complex q^2 plane. It is shown that the QCD prediction for R_{tau} agrees with
the measured value R_{tau} not only for conventional Lambda^{conv}_3 =
(618+-29) MeV but as well as for Lambda^{new}_3 = (1666+-7) MeV. The
polarization operator calculated using the renormgroup has nonphysical cut
[-Lambda^2_3, 0]. If Lambda_3 = Lambda^{conv}_3, the contribution of only
physical cut is deficient in the explanation of the ALEPH experiment. If
Lambda_3 = Lambda^{new}_3 the contribution of nonphysical cut is very small and
only the physical cut explains the ALEPH experiment. The new sum rules which
follow only from analytical properties of polarization operators are obtained.
Basing on the sum rules obtained, it is shown that there is an essential
disagreement between QCD perturbation theory and the tau-lepton hadronic decay
experiment at conventional value Lambda_3. In the evolution upwards to larger
energies the matching of r(q^2) (Eq.(12)) at the masses J/psi, Upsilon and 2m_t
was performed. The obtained value alpha_s(-m^2_z) = 0.141+-0.004 (at Lambda_3 =
Lambda^{new}_3) differs essentially from conventional value, but the
calculation of the values R(s) = sigma(e+e- -> hadrons)/sigma(e+e- -> mu+mu-),
R_l = Gamma(Z -> hadrons)/Gamma(Z -> leptons), alpha_s(-3 GeV^2), alpha_s(-2.5
GeV^2) does not contradict the experiments.Comment: 20 page
Matching Regge Theory to the OPE
The spectra of masses and decay constants for non-strange meson resonances in
the energy range 0--2.5 GeV is analyzed. It is known from meson phenomenology
that for given quantum numbers these spectra approximately follow linear
trajectories with a universal slope. These facts can be understood in terms of
an effective string description for QCD. For light meson states the
trajectories deviate noticeably from the linear behavior. We investigate the
possible corrections to the linear trajectories by matching two-point
correlators of quark currents to the Operator Product Expansion (OPE). We find
that the allowed modifications to the linear Regge behavior must decrease
rapidly with the principal quantum number. After fitting the lightest states in
each channel and certain low-energy constants the whole spectrum for meson
masses and residues is obtained in a satisfactory agreement with phenomenology.
We briefly speculate on possible implications for the QCD effective string.Comment: 24 pages, Latex, significant changes in discussion of fits, more refs
adde
New analytic running coupling in spacelike and timelike regions
The new model for the QCD analytic running coupling, proposed recently, is
extended to the timelike region. This running coupling naturally arises under
unification of the analytic approach to QCD and the renormalization group (RG)
formalism. A new method for determining the coefficients of the "analytized" RG
equation is elaborated. It enables one to take into account the higher loop
contributions to the new analytic running coupling (NARC) in a consistent way.
The expression for the new analytic running coupling, independent of the
normalization point, is obtained by invoking the asymptotic freedom condition.
It is shown that the difference between the values of the NARC in respective
spacelike and timelike regions is rather valuable for intermediate energies.
This is essential for the correct extracting of the running coupling from
experimental data. The new analytic running coupling is applied to the
description of the inclusive lepton decay. The consistent estimation of
the parameter is obtained here.Comment: REVTeX 3.1, 12 pages with 3 EPS figures; enlarged version is
published in Phys. Rev.
Testing an approximation to large-Nc QCD with a toy model
We consider a simple model of large-Nc QCD defined by a spectrum consisting
of an infinite set of equally spaced zero-width vector resonances. This model
is an excellent theoretical laboratory for investigating certain approximation
schemes which have been used recently in calculations of hadronic parameters,
such as the Minimal Hadronic Approximation. We also comment on some of the
questions concerning issues of local duality versus global duality and
finite-energy sum rules.Comment: LateX file; 16 pages, 7 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
Remark on the perturbative component of inclusive -decay
In the context of the inclusive -decay, we analyze various forms of
perturbative expansions which have appeared as modifications of the original
perturbative series. We argue that analytic perturbation theory, which combines
renormalization-group invariance and -analyticity, has significant merits
favoring its use to describe the perturbative component of -decay.Comment: 5 pages, ReVTEX, 2 eps figures. Revised paper includes clarifying
remarks and corrected references. To be published in Phys. Rev.
Factorization and Endpoint Singularities in Heavy-to-Light decays
We prove a factorization theorem for heavy-to-light form factors. Our result
differs in several important ways from previous proposals. A proper separation
of scales gives hard kernels that are free of endpoint singularities. A general
procedure is described for including soft effects usually associated with the
tail of wavefunctions in hard exclusive processes. We give an operator
formulation of these soft effects using the soft-collinear effective theory,
and show that they appear at the same order in the power counting as the hard
spectator contribution.Comment: 5 pages, Added details on comparison with the literatur