Low-mass scalar production in γγ\gamma \gamma scattering

We estimate the I=0 scalar meson $\sigma/f_0(600)$ $\gamma\gamma$ widths, from $\pi\pi$ and $\gamma\gamma$ scattering data below 700 MeV using an improved analytic K-matrix model.Comment: 3 pages, 2 figures, Talk given at QCD 08 (Montpellier 7-12th july 2008

The sigma and f_0(980) from K_e4+pi-pi, gamma-gamma scatterings, J/psi, phi to gamma sigma_B and D_s to l nu sigma_B

We extract the pole positions, hadronic and gamma-gamma widths of sigma and f_0(980, from pi-pi and gamma-gamma scattering data using an improved analytic K-matrix model. Our results favour a large gluon component for the sigma and a \bar ss or/and gluon component for the f_0(980) but neither a large four-quark nor a molecule component. Gluonium sigma_B production from J/psi, phi radiative and D_s semi-leptonic decays are also discussed.Comment: 4 pages, 5 figures, 6 tables, talk given by X.-G. Wang at QCD 10 (25th anniversary) 28th june-2nd july 2010 (Montpellier - FR

sigma and f_0(980) substructures from gamma-gamma to pi-pi, J/psi, phi radiative and D_s semi-leptonic decays

Using an improved "analytic K-matrix model", we reconsider the extraction of the sigma/f_0(600) and f_0(980) gamma-gamma widths from gamma-gamma to pi-pi scatterings data of Crystal Ball and Belle. Our main results are summarized in Tables 3 and 4. The averaged sigma "direct width" to gamma-gamma is 0.16(3) keV which confirms a previous result of [1] and which does neither favour a large four-quark (diquark-antidiquark) nor a molecule nor a pure \bar qq component. The "direct width" of the f_0(980) of 0.28(2) keV is much larger than the four-quark expectation but can be compatible with a \bar ss or gluonium component. We also found that the rescattering part of the amplitude is relatively large indicating an important contribution of the meson loops in the determination of the gamma-gamma total widths. This is mainly due to the large couplings of the sigma and f_0(980) to pi-pi and/or \bar KK, which can also be due to a light scalar gluonium with large OZI violating couplings but not necessary to a four-quark or molecule state. Our average results for the total (direct+rescattering) gamma-gamma widths: Gamma_sigma^{tot}= 3.08(82) keV, Gamma_{f_0}^{tot}= 0.16(1) keV} are comparable with the ones from dispersion relations and PDG values. Using the parameters from QCD spectral sum rules, we complete our analysis by showing that the production rates of unmixed scalar gluonia sigma_B(1) and G (1.5-1.6) agree with the data from J/\psi, phi radiative and D_s semi-leptonic decays.Comment: 11 pages, 6 figures (1 more figure added in Fig 6), 4 tables : version appeared on-line in doi:10.1016/j.physletb.2010.12.00

Proper identification of RR Lyrae Stars brighter than 12.5 mag

RR Lyrae stars are of great importance for investigations of Galactic structure. However, a complete compendium of all RR-Lyraes in the solar neighbourhood with accurate classifications and coordinates does not exist to this day. Here we present a catalogue of 561 local RR-Lyrae stars V_max less equal 12.5 mag according to the magnitudes given in the Combined General Catalogue of Variable Stars (GCVS) and 16 fainter ones. The Tycho2 catalogue contains about 100 RR Lyr stars. However, many objects have inaccurate coordinates in the GCVS, the primary source of variable star information, so that a reliable cross-identification is difficult. We identified RR Lyrae from both catalogues based on an intensive literature search. In dubious cases we carried out photometry of fields to identify the variable. Mennessier and Colome (2002) have published a paper with Tyc2-GCVS identifications, but we found that many of their identifications are wrong. Keywords: astrometry -- Stars: RR Lyrae stars -- Catalogues: Tycho-2 catalogue -- Catalogues: The HST Guide Star Catalogue, Version 1.2 -- Catalogues: Combined General Catalogue of Variable StarsComment: 5 pages with 2 figures; A and A accepted Online-Data are available under http://www.astro.uni-bonn.de/~gmaint

Can the gamma-gamma processes reveal the nature of the sigma ?

We reanalyse the gamma-gamma scattering data and conclude that in the mass region below 1 GeV the cross section for gamma-gamma to pi^0-pi^0 can be largely explained by the one pion exchange process with pi-pi rescattering. The radiative width of the sigma is estimated and a model dependent separation into contributions from direct gamma-gamma decay and decay through rescattering is obtained. We confront these findings with QCD spectral sum rule (QSSR) predictions and conclude that the sigma can have a large gluonium component in its wave function

Pion and muon production in electron-positron photon plasma

We study production and equilibration of pions and muons in relativistic electron-positron-photon plasma at a temperature $T\ll m_\mu, m_\pi$. We argue that the observation of pions and muons can be a diagnostic tool in the study of the initial properties of such a plasma formed by means of strong laser fields. Conversely, properties of muons and pions in thermal environment become accessible to precise experimental study.Comment: 16 pages, v3 imporved presentation in response to PRD review, v4 minor corrections presumably the "to be" published versio

How many Hipparcos Variability-Induced Movers are genuine binaries?

Hipparcos observations of some variable stars, and especially of long-period (e.g. Mira) variables, reveal a motion of the photocenter correlated with the brightness variation ({variability-induced mover -- VIM), suggesting the presence of a binary companion. A re-analysis of the Hipparcos photometric and astrometric data does not confirm the VIM solution for 62 among the 288 VIM objects (21%) in the Hipparcos catalogue. Most of these 288 VIMs are long-period (e.g. Mira) variables (LPV). The effect of a revised chromaticity correction, which accounts for the color variations along the light cycle, was then investigated. It is based on `instantaneous' $V-I$ color indices derived from Hipparcos and Tycho-2 epoch photometry. Among the 188 LPVs flagged as VIM in the Hipparcos catalogue, 89 (47%) are not confirmed as VIM after this improved chromaticity correction is applied. This dramatic decrease in the number of VIM solutions is not surprising, since the chromaticity correction applied by the Hipparcos reduction consortia was based on a fixed $V-I$ color. Astrophysical considerations lead us to adopt a more stringent criterion for accepting a VIM solution (first-kind risk of 0.27% instead of 10% as in the Hipparcos catalogue). With this more severe criterion, only 27 LPV stars remain VIM, thus rejecting 161 of the 188 (86%) of the LPVs defined as VIMs in the Hipparcos catalogue.Comment: 9 pages, 4 figures, accepted in A&

The sigma and f_0(980) from Ke4 + pi-pi scatterings data

We systematically reconsider, within an improved "analytic K-matrix model", the extraction of the sigma = f_0(600) and f_0(980) masses, widths and hadronic couplings using new Ke4 = K-->pi-pi e nu_e data on pi-pi phase shift below 390 MeV and different sets of pi-pi--> pi-pi / K-K scatterings data from 400 MeV to 1.4 GeV. Our results are summarized in Tables 1, 2 and 5. In units of MeV, the complex poles are: M_sigma=452(12) - i 260(15) and M_f=981(34) -i 18(11), which are comparable with some recent high-precision determinations and with PDG values. Besides some other results, we find: |g_{sigma K+K-}|/|g_{sigma pi+pi-}|=0.37(6) which confirms a sizeable g_{sigma K+K-} coupling found earlier, and which disfavours a large pi-pi molecule or four-quark component of the sigma, while its broad pi-pi width (relative to the one of the rho-meson) cannot be explained within a \bar qq scenario. The narrow pi-pi width of the f_0(980) and the large value: |g_{f K+K-}|/|g_{f pi+pi-}|=2.59(1.34), excludes its pure (\bar uu+\bar dd) content. A significant gluonium component eventually mixed with \bar qq appears to be necessary for evading the previous difficulties.Comment: 9 pages, 3 figures, 6 table

Observation of the Higgs Boson of strong interaction via Compton scattering by the nucleon

It is shown that the Quark-Level Linear $\sigma$ Model (QLL$\sigma$M) leads to a prediction for the diamagnetic term of the polarizabilities of the nucleon which is in excellent agreement with the experimental data. The bare mass of the $\sigma$ meson is predicted to be $m_\sigma=666$ MeV and the two-photon width $\Gamma(\sigma\to\gamma\gamma)=(2.6\pm 0.3)$ keV. It is argued that the mass predicted by the QLL$\sigma$M corresponds to the $\gamma\gamma\to\sigma\to NN$ reaction, i.e. to a $t$-channel pole of the $\gamma N\to N\gamma$ reaction. Large -angle Compton scattering experiments revealing effects of the $\sigma$ meson in the differential cross section are discussed. Arguments are presented that these findings may be understood as an observation of the Higgs boson of strong interaction while being part of the constituent quark.Comment: 17 pages, 6 figure