How can one understand the lightest scalars, especially the sigma

We discuss how the a_0(980), f_0(980), K^*_0(1430) and particularly the broad sigma resonance can be understood within a coupled channel framework, which includes all light two-pseudoscalar thresholds together with constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. All (qbar q) scalars are, when unitarized, strongly distorted by hadronic mass shifts, and the nonstrange isoscalar state becomes a very broad resonance, with its pole at 470-i250 MeV. We believe this is the sigma meson required by models for spontaneous breaking of chiral symmetry. Recently this light resonance has clearly been observed in D-> sigma pi-> 3pi by the E791 experiment at Fermilab, and we discuss how this decay channel can be predicted in a Constituent Quark Meson Model (CQM), which incorporates heavy quark and chiral symmetries. We also discuss the less well known phenomenon that with a large coupling there can appear two physical resonance poles on the second sheet although only one bare quark-antiquark state is put in. The f_0(980) and f_0(1370) resonance poles can thus be two manifestations of the same (sbar s) quark state. Both of these states are seen clearly in D_s-> 3pi by the E791 experiment, where (sbar s) intermediate states are expected to be dominant.Comment: 9 pages; Invited plenary talk by N.A. Tornqvist at the ''Biennial Conference on Low Energy Antiproton Physics'' (LEAP2000), Venice, Italy, August 20-26, 2000. To appear in Nucl. Phys. A (proc. suppl.

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 $q \overline q$ 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

Pion propagation in the linear sigma model at finite temperature

We construct effective one-loop vertices and propagators in the linear sigma model at finite temperature, satisfying the chiral Ward identities and thus respecting chiral symmetry, treating the pion momentum, pion mass and temperature as small compared to the sigma mass. We use these objects to compute the two-loop pion self-energy. We find that the perturbative behavior of physical quantities, such as the temperature dependence of the pion mass, is well defined in this kinematical regime in terms of the parameter m_pi^2/4pi^2f_pi^2 and show that an expansion in terms of this reproduces the dispersion curve obtained by means of chiral perturbation theory at leading order. The temperature dependence of the pion mass is such that the first and second order corrections in the above parameter have the same sign. We also study pion damping both in the elastic and inelastic channels to this order and compute the mean free path and mean collision time for a pion traveling in the medium before forming a sigma resonance and find a very good agreement with the result from chiral perturbation theory when using a value for the sigma mass of 600 MeV.Comment: 18 pages, 11 figures, uses RevTeX and epsfig. Expanded conclusions, added references. To appear in Phys. Rev.

Identification of Quantitative Trait Loci for Plant Height, Crown Diameter, and Plant Biomass in a Pseudo-F2 Population of Switchgrass

Switchgrass (Panicum virgatum) is a perennial warm-season grass that produces high biomass yield. Identification of mechanisms for genetic regulation of biomass traits has potential to facilitate genetic manipulation of switchgrass for enhancing biomass yield. The objective of this study was to identify quantitative trait loci for biomass-related traits in a pseudo-F2 population of switchgrass derived from an upland cross with a lowland switchgrass cultivar. Plant height (HT), crown diameter (CD), and plant biomass (PB) were assessed in field studies in 2015 and 2016. Plant height was positively correlated with PB in both years but only correlated with CD in 2016. Positive correlations between CD and PB were found in both years. Six quantitative trait loci (QTLs) were detected, including three QTLs on chromosome 2b for HT (2015) or CD (2016), two 2 QTLs on chromosome 2a for CD and PB in 2016, and one QTL on chromosome 5b for CD in 2016. The logarithm of the odds scores for these QTLs ranged from 4.9 to 8.2, and percentage variance explained ranged from 7.1 to 12.9%. One QTL on chromosome 2b appeared to simultaneously control HT in 2015 and CD in 2016. Homologs of candidate genes related to cell wall development and biosynthesis, hormone regulation, and metabolism were identified within the confidence interval of these QTLs. The findings from this study indicate that these QTLs can be important signals for genetic control of switchgrass growth

Scalar meson dynamics in Chiral Perturbation Theory

A comparison of the linear sigma model (L$\sigma$M) 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 $p^4$ ChPT Lagrangian are fixed in terms of scalar meson masses. Present values of these low energy constants are compatible with the L$\sigma$M dynamics. We conclude that more accurate values would be most useful either to falsify the L$\sigma$M 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

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

Masses of heavy tetraquarks in the relativistic quark model

The masses of heavy tetraquarks with hidden charm and bottom are calculated in the framework of the relativistic quark model. The tetraquark is considered as the bound state of a heavy-light diquark and antidiquark. The light quark in a heavy-light diquark is treated completely relativistically. The internal structure of the diquark is taken into account by calculating the diquark-gluon form factor in terms of the diquark wave functions. New experimental data on charmonium-like states above open charm threshold are discussed. The obtained results indicate that the X(3872) can be the tetraquark state with hidden charm. The masses of ground state tetraquarks with hidden bottom are found to be below the open bottom threshold.Comment: 10 pages, 1 figure, minor changes, version to be published in Phys.Lett.

Beyond CP violation: hadronic physics at BaBar

I report on recent studies of hadronic physics performed by the BaBar Collaboration. Emphasis is given to the measurement of the properties of newly discovered charmed hadrons and to the searches for light and heavy pentaquarks.Comment: 14 pages, 20 postscript figues, contributed to the Proceedings of the First APS Topical Group Meeting on Hadron Physics, Fermilab, Batavia, IL (October 24-26, 2004

Studying Kaon-pion S-wave scattering in K-matrix formalism

We generalize our previous work on \pi\pi scattering to K\pi scattering, and re-analyze the experiment data of K\pi scattering below 1.6 GeV. Without any free parameter, we explain K\pi I=3/2 S-wave phase shift very well by using t-channel rho and u-channel K^* meson exchange. With the t-channel and u-channel meson exchange fixed as the background term, we fit the K\pi I=1/2 S-wave data of the LASS experiment quite well by introducing one or two s-channel resonances. It is found that there is only one s-channel resonance between K\pi threshold and 1.6 GeV, i.e., K_0^*(1430) with a mass around 1438~1486 MeV and a width about 346 MeV, while the t-channel rho exchange gives a pole at (450-480i) MeV for the amplitude.Comment: REVTeX4 file, 11 pages and 3 figure