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

Why the high lying glueball does not mix with the neighbouring f0f_0

Chiral symmetry restoration in high-lying hadron spectra implies that hadrons which belong to different irreducible representations of the parity-chiral group cannot mix. This explains why the $f_0(2102 \pm 13)$, which was suggested to be a glueball, and hence must belong to the scalar (0,0) representation of the chiral group, cannot mix with the neighbouring $f_0(2040 \pm 38)$, which was interpreted as a $n\bar n$ state, and that belongs to the $(1/2,1/2)$ representation of the chiral group. If confirmed, then we have an access to a "true" glueball of QCD.Comment: 4 pages, LaTeX, final version, Eur. Phys. J. A 19 (2004) 15

Mechanism for a next-to-lowest lying scalar meson nonet

Recent work suggests the existence of a non-conventional lowest-lying scalar nonet containing the a0(980). Then the a0(1450) and also the K0*(1430) are likely candidates to belong to a conventional p-wave $q \bar q$ nonet. However a comparison of their properties with those expected on this basis reveals a number of puzzling features. It is pointed out that these puzzles can be resolved in a natural and robust way by assuming a ``bare'' conventional p-wave scalar $q \bar q$ nonet to mix with a lighter four quark $qq \bar q \bar q$ scalar nonet to form new ``physical'' states. The essential mechanism is driven by the fact that the isospinor is lighter than the isovector in the unmixed $qq \bar q \bar q$ multiplet.Comment: 22 pages, 6 figure

Three channel model of meson-meson scattering and scalar meson spectroscopy

New solutions on the scalar -- isoscalar $\pi\pi$ phase shifts are analysed together with previous $K\bar{K}$ results using a separable potential model of three coupled channels ($\pi\pi$, $K\bar{K}$ and an effective $2\pi 2\pi$ system). Model parameters are fitted to two sets of solutions obtained in a recent analysis of the CERN-Cracow-Munich measurements of the $\pi^- p_{\uparrow} \to \pi^+ \pi^- n$ reaction on a polarized target. A relatively narrow (90 -- 180 MeV) scalar resonance $f_0(1400-1460)$ is found, in contrast to a much broader ($\Gamma \approx 500$ MeV) state emerging from the analysis of previous unpolarized target data.Comment: 10 Latex pages + 6 postscript figure

Exposure to diesel exhaust induces changes in EEG in human volunteers

Background: Ambient particulate matter and nanoparticles have been shown to translocate to the brain, and potentially influence the central nervous system. No data are available whether this may lead to functional changes in the brain. Methods: We exposed 10 human volunteers to dilute diesel exhaust (DE, 300 μg/m3) as a model for ambient PM exposure and filtered air for one hour using a double blind randomized crossover design. Brain activity was monitored during and for one hour following each exposure using quantitative electroencephalography (QEEG) at 8 different sites on the scalp. The frequency spectrum of the EEG signals was used to calculate the median power frequency (MPF) and specific frequency bands of the QEEG. Results: Our data demonstrate a significant increase in MPF in response to DE in the frontal cortex within 30 min into exposure. The increase in MPF is primarily caused by an increase in fast wave activity (β2) and continues to rise during the 1 hour post-exposure interval. Conclusion: This study is the first to show a functional effect of DE exposure in the human brain, indicating a general cortical stress response. Further studies are required to determine whether this effect is mediated by the nanoparticles in DE and to define the precise pathways involved

Tracking the sea-level signature of the 8.2 ka cooling event: New constraints from the Mississippi Delta

The ever increasing need for accurate predictions of global environmental change under greenhouse conditions has sparked immense interest in an abrupt, century‐scale cooling around 8200 years ago, with a focal point in the North Atlantic and with hemispheric teleconnections. Despite considerable progress in the unraveling of this striking feature, including a conceivable driving mechanism (rapid drainage of proglacial Lake Agassiz/Ojibway and a resulting reduced strength of North Atlantic thermohaline circulation), several key questions remain unanswered. One salient aspect concerns the total amount of freshwater released during this catastrophic event, likely echoed by a near‐instantaneous eustatic sea‐level rise. So far, no attempts have been made to perform high‐resolution sea‐level studies that explicitly focus on this critical time interval. Here, we present new data from the Mississippi Delta suggestive of abrupt sea‐level rise associated with the 8.2 ka event. However, the amount of sea‐level rise was likely less than ∼1.2 m, corresponding to a meltwater volume of less than ∼4.3 1014 m3; values lower than estimates used by several recent studies