135 research outputs found
Comment on Intrinsic and dynamically generated scalar meson states
The scalar-meson assignments of Shakin and Wang in a generalized
Nambu--Jona-Lasinio model are contradicted by recent experimental information.
Also the strict distinction made by these authors between ``intrinsic'' and
``dynamically generated'' states is contested, as well as a number of other
statements.Comment: 7 pages, (v2 cosmetics, v3 corrections in one reference), to be
published in Phys.Rev.
Two-hadron semi-inclusive production including subleading twist
We extend the analysis of two-hadron fragmentation functions to the
subleading twist, discussing also the issue of color gauge invariance. Our
results can be used anywhere two unpolarized hadrons are semi-inclusively
produced in the same fragmentation region, also at moderate values of the hard
scale Q. Here, we consider the example of polarized deep-inelastic production
of two hadrons and we give a complete list of cross sections and spin
asymmetries up to subleading twist. Among the results, we highlight the
possibility of extracting the transversity distribution with longitudinally
polarized targets and also the twist-3 distribution e(x), which is related to
the pion-nucleon sigma term and to the strangeness content of the nucleon.Comment: 16 pages, RevTeX4, 5 figures, revised notation of several formulae,
added text in Secs. III-V, added reference
A QCD Analysis of the Mass Structure of the Nucleon
{}From the deep-inelastic momentum sum rule and the trace anomaly of the
energy-momentum tensor, I derive a separation of the nucleon mass into the
contributions of the quark and gluon kinetic and potential energies, the quark
masses, and the trace anomaly.Comment: 9 pages, MIT-CTP #2368, revtex with 1 tabl
Positive Parity Scalar Mesons in the 1-2 GeV Mass Range
Based on the observation that K_0(1430) is lighter than its SU_3 counterpart,
a_0(1450), we examine the possibility that these particles, together with
f_0(1370), f_0(1500) and f_0(1710), fill a tetraquark recurrence of the sub-GeV
0^{++} nonet mixed with a glueball state. We find the picture to be consistent
with the known data about the three f_0 resonances, more than the q-qbar
hypothesis. Conventional spin-orbit coupling suggests the q-qbar, P-wave, nonet
to lie around 1200 MeV. We review possible experimental indications of a scalar
isovector resonance at 1.29 GeV, first observed by OBELIX in p-pbar
annihilation.Comment: 12 pages, 9 figures. Extended version. References added. Results and
conclusions unchange
Resummation of mass terms in perturbative massless quantum field theory
The neutral massless scalar quantum field in four-dimensional
space-time is considered, which is subject to a simple bilinear
self-interaction. Is is well-known from renormalization theory that adding a
term of the form to the Lagrangean has the formal
effect of shifting the particle mass from the original zero value to m after
resummation of all two-leg insertions in the Feynman graphs appearing in the
perturbative expansion of the S-matrix. However, this resummation is
accompanied by some subtleties if done in a proper mathematical manner.
Although the model seems to be almost trivial, is shows many interesting
features which are useful for the understanding of the convergence behavior of
perturbation theory in general. Some important facts in connection with the
basic principles of quantum field theory and distribution theory are
highlighted, and a remark is made on possible generalizations of the
distribution spaces used in local quantum field theory. A short discussion how
one can view the spontaneous breakdown of gauge symmetry in massive gauge
theories within a massless framework is presented.Comment: 15 pages, LaTeX (style files included), one section adde
Large Nc and Chiral Dynamics
We study the dependence on the number of colors of the leading pi pi
scattering amplitude in chiral dynamics. We demonstrate the existence of a
critical number of colors for and above which the low energy pi pi scattering
amplitude computed from the simple sum of the current algebra and vector meson
terms is crossing symmetric and unitary at leading order in a truncated and
regularized 1/Nc expansion. The critical number of colors turns out to be Nc=6
and is insensitive to the explicit breaking of chiral symmetry.
Below this critical value, an additional state is needed to enforce the
unitarity bound; it is a broad one, most likely of "four quark" nature.Comment: RevTeX4, 6 fig., 5 page
Study of the , , and in the radiative decays
In this paper we present an approach to study the radiative decay modes of
the into a photon and one of the tensor mesons ,
, as well as the scalar ones and .
Especially we compare predictions that emerge from a scheme where the states
appear dynamically in the solution of vector meson--vector meson scattering
amplitudes to those from a (admittedly naive) quark model. We provide evidence
that it might be possible to distinguish amongst the two scenarios, once
improved data are available.Comment: The large Nc argument improved; version published in EPJA
A purely algebraic construction of a gauge and renormalization group invariant scalar glueball operator
This paper presents a complete algebraic proof of the renormalizability of
the gauge invariant operator to all orders of
perturbation theory in pure Yang-Mills gauge theory, whereby working in the
Landau gauge. This renormalization is far from being trivial as mixing occurs
with other gauge variant operators, which we identify explicitly. We
determine the mixing matrix to all orders in perturbation theory by using
only algebraic arguments and consequently we can uncover a renormalization
group invariant by using the anomalous dimension matrix derived from
. We also present a future plan for calculating the mass of the lightest
scalar glueball with the help of the framework we have set up.Comment: 17 page
f0(980) meson as a K bar K molecule in a phenomenological Lagrangian approach
We discuss a possible interpretation of the f0(980) meson as a hadronic
molecule - a bound state of K and bar K mesons. Using a phenomenological
Lagrangian approach we calculate the strong f0(980) to pi pi and
electromagnetic f0(980) to gamma gamma decays. The compositeness condition
provides a self-consistent method to determine the coupling constant between f0
and its constituents, K and bar K. Form factors governing the decays of the
f0(980) are calculated by evaluating the kaon loop integrals. The predicted
f0(980) to pi pi and f0(980) to gamma gamma decay widths are in good agreement
with available data and results of other theoretical approaches.Comment: 21 pages, 11 figures, revised version accepted for publication in
Eur. Phys. J.
Search for the decay in the momentum region
We have searched for the decay in the kinematic
region with pion momentum below the peak. One event was
observed, consistent with the background estimate of . This
implies an upper limit on
(90% C.L.), consistent with the recently measured branching ratio of
, obtained using the standard model
spectrum and the kinematic region above the peak. The
same data were used to search for , where is a weakly
interacting neutral particle or system of particles with .Comment: 4 pages, 2 figure
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