UNDERSTANDING THE SCALAR MESON qqˉq\bar q NONET

It is shown that one can fit the available data on the a0(980), f0(980), f0(1300) and K*0(1430) mesons as a distorted 0++ qq bar nonet using very few (5-6) parameters and an improved version of the unitarized quark model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. The parameters include a bare uu bar or dd bar mass, an over-all coupling constant, a cutoff and a strange quark mass of 100 MeV, which is in accord with expectations from the quark model. It is found that in particular for the a0(980) and f0(980) the KK bar component in the wave function is large, i.e., for a large fraction of the time the qq bar state is transformed into a virtual KK bar pair. This KK bar component, together with a similar component of eta' pi for the a0(980) , and eta eta, eta eta' and eta' eta' components for the f0(980), causes the substantial shift to a lower mass than what is naively expected from the qq bar component alone. Mass, width and mixing parameters, including sheet and pole positions, of the four resonances are given, with a detailed pedagogical discussion of their meaning.Comment: 35 pages in plain latex (ZPC in press), 10 figures obtainable from the author ([email protected]) with regular mail or as a large PS fil

A new look at scalar mesons

Light scalar mesons are found to fit rather well a diquark-antidiquark description. The resulting nonet obeys mass formulae which respect, to a good extent, the OZI rule. OZI allowed strong decays are reasonably reproduced by a single amplitude describing the switch of a qbar-q pair, which transforms the state into two colourless pseudoscalar mesons. Predicted heavy states with one or more quarks replaced by charm or beauty are briefly described; they should give rise to narrow states with exotic quantum numbers.Comment: 4 pages, 1 figure, misprints corrected, references added, accepted for publication in Phys. Rev. Let

Estimating sigma-meson couplings from D \to 3\pi decays

Using recent experimental evidence from E791 on the sigma meson in D \to 3\pi decays, we study the relevant couplings in D \to \sigma \pi and \sigma \to \pi\ pi within the accepted theoretical framework for non leptonic D decays. We also review the linear sigma model, finding that it gives a description which is consistent with the experimental data.Comment: 6 pages, no figures. Final version accepted for publication as a Brief Report in Physical Review

The structure of f0(980)f_0(980) from charmed mesons decays

We use the QCD sum rules to evaluate the form factors associated with the semileptonic decays of $D_s$ and $D$ mesons into $f_0(980)$. We consider the $f_0(980)$ meson as a quark-antiquark state with a mixture of strange and light components. The decay rates are evaluated in terms of the mixing angle. Using the same form factors to evaluate nonleptonic decays in the framework of the factorization approximation we conclude that the importance of the light quarks in $f_0(980)$ is not negligible.Comment: 11 pages, 2 figures, using Revtex

Diagnostic Decays of the X(3872)

The unusual properties of the X(3872) have led to speculation that it is a weakly bound state of mesons, chiefly $D^0\bar D^{0*}$. Tests of this hypothesis are investigated and it is proposed that measuring the $3\pi J/\psi$, $\gamma J/\psi$, $\gamma \psi'$, $\bar K K^*$, and $\pi\rho$ decay modes of the $X$ will serve as a definitive diagnostic of the molecule hypothesis.Comment: 6 pages revtex4, 3 eps figure

Production and detection of doubly charmed tetraquarks

The feasibility of tetraquark detection is studied. For the cc\bar{u}\bar{d} tetraquark we show that in present (SELEX, Tevatron, RHIC) and future facilities (LHCb, ALICE) the production rate is promising and we propose some detectable decay channels.Comment: 6 pages, 5 figure

QCD sum rule approach for the light scalar mesons as four-quark states

We study the two point-function for the scalar mesons $\sigma, \kappa, f_0(980)$ and $a_0(980)$ as diquak-antidiquark states. We also study the decays of these mesons into $\pi\pi$, $K\pi$ and $K\bar{K}$. We found that the couplings are consistent with existing experimental data, pointing in favor of the four-quark structure for the light scalar mesons.Comment: 6 pages, 4 figure

Climate change projections for variables affecting road networks in Europe

Global climate change will affect road networks during this century. The effects will be different in various parts of the world due to differences in local climate change and in the structure and properties of roads. In this paper, climate change projections are presented for climate variables that are most likely to affect the long-term performance of road networks in Europe. We apply four regional climate simulations up to the year 2100 using two plausible future emission scenarios. The results show that the changing climate will require significant adaptation measures in the near future in order to maintain the operability of the European road network

On Deusons or Deuteronlike Meson-Meson Bound States

The systematics of deuteronlike two-meson bound states, {\it deusons}, is discussed. Previous arguments that many of the present non-$q\bar q$ states are such states are elaborated including, in particular, the tensor potential. For pseudoscalar states the important observation is made that the centrifugal barrier from the P-wave can be overcome by the $1/r^2$ and $1/r^3$ terms of the tensor potential. In the heavy meson sector one-pion exchange alone is strong enough to form at least deuteron-like $B\bar B^*$ and $B^*\bar B^*$ composites bound by approximately 50 MeV, while $D\bar D^*$ and $D^*\bar D^*$ states are expected near the threshold.Comment: Invited talk at the Hadron93 International Conf. on Hadron Spectroscopy, Como, Italy 22.-25.6. 1993. 5 pages in LATEX HU-SEFT R 1993-13

Total Widths And Slopes From Complex Regge Trajectories

Maximally complex Regge trajectories are introduced for which both Re $\alpha(s)$ and Im $\alpha(s)$ grow as $s^{1-\epsilon}$ ($\epsilon$ small and positive). Our expression reduces to the standard real linear form as the imaginary part (proportional to $\epsilon$) goes to zero. A scaling formula for the total widths emerges: $\Gamma_{TOT}/M\to$ constant for large M, in very good agreement with data for mesons and baryons. The unitarity corrections also enhance the space-like slopes from their time-like values, thereby resolving an old problem with the $\rho$ trajectory in $\pi N$ charge exchange. Finally, the unitarily enhanced intercept, $\alpha_{\rho}\approx 0.525$, \nolinebreak is in good accord with the Donnachie-Landshoff total cross section analysis.Comment: 9 pages, 3 Figure