Nature of the f_0(600) from its N_c dependence at two loops in unitarized Chiral Perturbation Theory

By using unitarized two-loop Chiral Perturbation Theory partial waves to describe pion-pion scattering we find that the dominant component of the lightest scalar meson does not follow the q-qbar dependence on the number of colors that, in contrast, is obeyed by the lightest vectors. The method suggests that a subdominant q-qbar component of the f_0(600) possibly originates around 1 GeV.Comment: 4 pages, 1 Figure. To appear in Phys. Rev. Let

The preliminary lattice QCD calculation of κ\kappa meson decay width

We present a direct lattice QCD calculation of the $\kappa$ meson decay width with the s-wave scattering phase shift for the isospin $I=1/2$ pion-kaon ($\pi K$) system. We employ a special finite size formula, which is the extension of the Rummukainen-Gottlieb formula for the $\pi K$ system in the moving frame, to calculate the scattering phase, which indicates a resonance around $\kappa$ meson mass. Through the effective range formula, we extract the effective $\kappa \to \pi K$ coupling constant $g_{\kappa \pi K} = 4.54(76)$ GeV and decay width $\Gamma = 293 \pm 101$ MeV. Our simulations are done with the MILC gauge configurations with $N_f=2+1$ flavors of the "Asqtad" improved staggered dynamical sea quarks on a $16^3\times48$ lattice at $(m_\pi + m_K) / m_\kappa \approx 0.8$ and lattice spacing $a \approx 0.15$ fm.Comment: To make it concise. arXiv admin note: text overlap with arXiv:1110.1422, but much of v1 text overlap with articles by same and other authors remove

How Resonances can synchronise with Thresholds

The mechanism by which a threshold may capture a resonance is examined. It involves a threshold cusp interfering constructively with either or both (i) a resonance produced via confinement, (ii) attractive t- and u-channel exchanges. The fo(980), X(3872) and Z(4430) are studied in detail. The fo(980) provides a valuable model of the locking mechanism. The X(3872) is too narrow to be fitted by a cusp, and requires either a resonance or virtual state. The Z(4430) can be fitted as a resonance but also can be fitted successfully by a cusp with no nearby resonant pole.Comment: 19 pages, 6 figures. Replaces 0709.125

The K^*_0(800) scalar resonance from Roy-Steiner representations of pi K scattering

We discuss the existence of the light scalar meson K^*_0(800) (also called kappa) in a rigorous way, by showing the presence of a pole in the pi K --> pi K amplitude on the second Riemann sheet. For this purpose, we study the domain of validity of two classes of Roy-Steiner representations in the complex energy plane. We prove that one of them is valid in a region sufficiently broad in the imaginary direction. From this representation, we compute the l=0 partial wave in the complex plane with neither additional approximation nor model dependence, relying only on experimental data. A scalar resonance with strangeness S=1 is found with the following mass and width: E_kappa = 658 \pm 13 MeV and Gamma_kappa = 557 \pm 24 MeV.Comment: 16 pages, 8 figures. Domain of validity of a Roy-Steiner representation corrected and enlarged, and features of the K^*_0(800) pole discussed in more details. Conclusions unchange

The two-pion spectra for the reaction \pi^- p -> \pi^0\pi^0 n at 38 GeV/c pion momentum and combined analysis of the GAMS, Crystal Barrel and BNL data

We perform the K-matrix analysis of meson partial waves with IJ^{PC} =00^{++}, 10^{++}, 02^{++}, 12^{++} basing on GAMS data on \pi^-p -> \pi^0\pi^0 n, \eta\eta n, \eta\eta' n together with BNL data on \pi^-p -> K\bar K n and Crystal Barrel data on p\bar p (at rest) -> \pi^0\pi^0\pi^0, \pi^0\eta\eta, \pi^0\pi^0\eta. The positions of the amplitude poles (physical resonances) are determined as well as the positions of the K-matrix poles (bare states) and the values of bare state couplings to two-meson channels. Nonet classification of the determined bare states is discussed.Comment: LaTex, 15 pages and 10 figure

A Uniform Description of the States Recently Observed at B-factories

The newly found states Y(4260), Y(4361), Y(4664) and Z$^\pm$(4430) stir broad interest in the study of spectroscopy in a typical charmonium scale. The Y(4260) which was observed earlier has been interpreted as hybrid, molecular state, and baryonium, etc. In this note we show for the first time that these new structures, which are hard to be interpreted as charmonium states, can be systematically embedded into an extended baryonium picture. According to this assignment, the so far known characters of these states are understandable. And, in the same framework, we make some predictions for experimenters to measure in the future.Comment: 6 pages in Latex. to appear in J.Phys.

Meson-Baryon Form Factors in Chiral Colour Dielectric Model

The renormalised form factors for pseudoscalar meson-baryon coupling are computed in chiral colour dielectric model. This has been done by rearranging the Lippmann-Schwinger series for the meson baryon scattering matrix so that it can be expressed as a baryon pole term with renormalized form factors and baryon masses and the rest of the terms which arise from the crossed diagrams. Thus we are able to obtain an integral equation for the renormalized meson-baryon form factors in terms of the bare form factors as well as an expression for the meson self energy. This integral equation is solved and renormalized meson baryon form factors and renormalized baryon masses are computed. The parameters of the model are adjusted to obtain a best fit to the physical baryon masses. The calculations show that the renormalized form factors are energy-dependent and differ from the bare form factors primarily at momentum transfers smaller than 1 GeV. At nucleon mass, the change in the form factors is about 10% at zero momentum transfer. The computed form factors are soft with the equivalent monopole cut-off mass of about 500 MeV. The renormalized coupling constants are obtained by comparing the chiral colour dielectric model interaction Hamiltonian with the standard form of meson-nucleon interaction Hamiltonian. The ratio of $\Delta N\pi$ and $NN\pi$ coupling constants is found to be about 2.15. This value is very close to the experimental value.Comment: 16 pages, 7 postscript figure

Isoscalar off-shell effects in threshold pion production from pd collisions

We test the presence of pion-nucleon isoscalar off-shell effects in the $pd\to \pi^+ t$ reaction around the threshold region. We find that these effects significantly modify the production cross section and that they may provide the missing strength needed to reproduce the data at threshold.Comment: 6 pages, REVTeX, twocolumn, including 3 figures (Postscript), uses psfig, updated and extended versio

Parity Doubling Among the Baryons

We study the evidence for and possible origins of parity doubling among the baryons. First we explore the experimental evidence, finding a significant signal for parity doubling in the non-strange baryons, but little evidence among strange baryons. Next we discuss potential explanations for this phenomenon. Possibilities include suppression of the violation of the flavor singlet axial symmetry ($U(1)_{A}$) of QCD, which is broken by the triangle anomaly and by quark masses. A conventional Wigner-Weyl realization of the $SU(2)_{L}\times SU(2)_{R}$ chiral symmetry would also result in parity doubling. However this requires the suppression of families of \emph{chirally invariant} operators by some other dynamical mechanism. In this scenario the parity doubled states should decouple from pions. We discuss other explanations including connections to chiral invariant short distance physics motivated by large $N_{c}$ arguments as suggested by Shifman and others, and intrinsic deformation of relatively rigid highly excited hadrons, leading to parity doubling on the leading Regge trajectory. Finally we review the spectroscopic consequences of chiral symmetry using a formalism introduced by Weinberg, and use it to describe two baryons of opposite parity.Comment: 32 pages, 8 figures; v2 revised and expanded; submitted to Phys. Re

Systematization of tensor mesons and the determination of the 2++2^{++} glueball

It is shown that new data on the $(J^{PC}=2^{++})$-resonances in the mass range $M\sim1700-2400$MeV support the linearity of the $(n,M^2)$-trajectories, where $n$ is the radial quantum number of quark--antiquark state. In this way all vacancies for the isoscalar tensor $q\bar q$-mesons in the range up to 2450 MeV are filled in. This allows one to fix the broad $f_2$-state with $M=2000\pm30$MeV and $\Gamma=530\pm40$MeV as the lowest tensor glueball. PACS numbers: 14.40.-n, 12.38.-t, 12.39.-MkComment: 10 pages, 1 figur