383 research outputs found
The s-sbar and K-Kbar nature of f_0(980) in D_s decays
We examine the D_s -> f_0(980) pi amplitude through a constituent quark-meson
model, incorporating heavy quark and chiral symmetries, finding a good
agreement with the recent E791 data analysis of D_s -> 3pi via f_0(980). The
f_0(980) resonance is considered at the moment of production as an s sbar
state, later evolving to a superposition of mainly s sbar and K Kbar. The
analysis is also extended to the more frequent process D_s -> phi pi.Comment: 8 pages, 5 figure
Unquenching the scalar glueball
Computations in the quenched approximation on the lattice predict the
lightest glueball to be a scalar in the 1.5-1.8 GeV region. Here we calculate
the dynamical effect the coupling to two pseudoscalars has on the mass, width
and decay pattern of such a scalar glueball. These hadronic interactions allow
mixing with the scalar nonet, which is largely fixed by the
well-established K_0^*(1430). This non-perturbative mixing means that, if the
pure gluestate has a width to two pseudoscalar channels of ~100 MeV as
predicted on the lattice, the resulting hadron has a width to these channels of
only ~30 MeV with a large eta-eta component. Experimental results need to be
reanalyzed in the light of these predictions to decide if either the f_0(1500)
or an f_0(1710) coincides with this dressed glueball.Comment: 12 pages, LaTex, 3 Postscript figure
A chiral model for bar{q}q and bar{q}bar{q}qq$ mesons
We point out that the spectrum of pseudoscalar and scalar mesons exhibits a
cuasi-degenerate chiral nonet in the energy region around 1.4 GeV whose scalar
component has a slightly inverted spectrum. Based on the empirical linear
rising of the mass of a hadron with the number of constituent quarks which
yields a mass around GeV for tetraquarks, we conjecture that this
cuasi-chiral nonet arises from the mixing of a chiral nonet composed of
tetraquarks with conventional bar{q}q states. We explore this possibility in
the framework of a chiral model assuming a tetraquark chiral nonet around 1.4
GeV with chiral symmetry realized directly. We stress that U_{A}(1)
transformations can distinguish bar{q}q from tetraquark states, although it
cannot distinguish specific dynamics in the later case. We find that the
measured spectrum is consistent with this picture. In general, pseudoscalar
states arise as mainly bar{q}q states but scalar states turn out to be strong
admixtures of bar{q}q and tetraquark states. We work out also the model
predictions for the most relevant couplings and calculate explicitly the strong
decays of the a_{0}(1450) and K_{0}^*(1430) mesons. From the comparison of some
of the predicted couplings with the experimental ones we conclude that
observable for the isovector and isospinor sectors are consistently described
within the model. The proper description of couplings in the isoscalar sectors
would require the introduction of glueball fields which is an important missing
piece in the present model.Comment: 20 pages, 3 figure
Scalar meson dynamics in Chiral Perturbation Theory
A comparison of the linear sigma model (LM) and Chiral Perturbation
Theory (ChPT) predictions for pion and kaon dynamics is presented. Lowest and
next-to-leading order terms in the ChPT amplitudes are reproduced if one
restricts to scalar resonance exchange. Some low energy constants of the order
ChPT Lagrangian are fixed in terms of scalar meson masses. Present values
of these low energy constants are compatible with the LM dynamics. We
conclude that more accurate values would be most useful either to falsify the
LM or to show its capability to shed some light on the controversial
scalar physics.Comment: 9 pages, REVTeX 4.0. Final version accepted for publicatio
Analysis of preliminary data on reaction
We perform the analysis of the preliminary data on reaction simultaneously with the data on
scattering and reactions and
. It is found that the meson mass
MeV and .Comment: 8 pages, revtex, 3 ps files of figures, minor change
J/\Psi \to \phi \pi \pi (K \bar{K}) decays, chiral dynamcis and OZI violation
We have studied the invariant mass distributions of the \pi\pi and K \bar{K}
systems for invariant masses up to 1.2 GeV from the J/\Psi \to \phi
\pi\pi(K\bar{K}) decays. The approach exploits the connection between these
processes and the \pi\pi and K\bar{K} strange and non-strange scalar form
factors by considering the \phi meson as a spectator. The calculated scalar
form factors are then matched with the ones from next-to-leading order chiral
perturbation theory, including the calculation of the the K\bar{K} scalar form
factors. Final state interactions in the J/\Psi \to \phi \pi\pi (K\bar{K})
processes are taken into account as rescattering effects in the system of the
two pseudoscalar mesons. A very good agreement with the experimental data from
DM2 and MARK-III is achieved. Furthermore, making use of SU(3) symmetry, the
S-wave contribution to the \pi^+\pi^- event distribution in the J/\Psi \to
\omega \pi^+\pi^- reaction is also given and the data up to energies of about
0.7 GeV are reproduced. These decays of the J/\Psi to a vector and a pair of
pseudoscalars turn out to be very sensitive to OZI violating physics which we
parametrize in terms of a direct OZI violation parameter and the chiral
perturbation theory low energy constants L_4^r and L_6^r. These constants all
come out very different from zero, lending further credit to the statement that
the OZI rule is not operative in the scalar 0^{++} channel.Comment: revtex, 21 pages, 10 figures, extended discussion of the model in
section 2 and some minor corrections, version accepted for publication in
Nucl. Phys.
Chiral symmetry and quantum hadro-dynamics
Using the linear sigma model, we study the evolutions of the quark condensate
and of the nucleon mass in the nuclear medium. Our formulation of the model
allows the inclusion of both pion and scalar-isoscalar degrees of freedom. It
guarantees that the low energy theorems and the constrains of chiral
perturbation theory are respected. We show how this formalism incorporates
quantum hadro-dynamics improved by the pion loops effects.Comment: 24 pages, 2 figure
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
B->rho pi decays, resonant and nonresonant contributions
We point out that a new contribution to B decays to three pions is relevant
in explaining recent data from the CLEO and BABAR collaborations, in particular
the results on quasi-two-body decays via a rho meson. We also discuss the
relevance of these contribution to the measurement of CP violations.Comment: 5 pages, 2 figures, few references and minor comments adde
Chiral Lagrangian for strange hadronic matter
A generalized Lagrangian for the description of hadronic matter based on the
linear -model is proposed. Besides the baryon
octet, the spin-0 and spin-1 nonets, a gluon condensate associated with broken
scale invariance is incorporated. The observed values for the vacuum masses of
the baryons and mesons are reproduced. In mean-field approximation, vector and
scalar interactions yield a saturating nuclear equation of state. We discuss
the difficulties and possibilities to construct a chiral invariant baryon-meson
interaction that leads to a realistic equation of state. It is found that a
coupling of the strange condensate to nucleons is needed to describe the
hyperon potentials correctly. The effective baryon masses and the appearance of
an abnormal phase of nearly massless nucleons at high densities are examined. A
nonlinear realization of chiral symmetry is considered, to retain a Yukawa-type
baryon-meson interaction and to establish a connection to the Walecka-model.Comment: Revtex, submitted to Phys. Rev.
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