Search

We perform a combined study of the two hadronic decays $D^+\to K^-\pi^+\pi^+$ and $D_s^+\to K^+K^+\pi^-$ using a detailed analysis of the semileptonic decays $D^+\to K^-\pi^+ \ell^+\nu_\ell$ ($\ell=e, \mu$) thanks to the high-statistics dataset provided by the BESIII Collaboration. We propose simple and suitable amplitude parametrizations of the studied reactions that shall be of interest to experimentalists for upcoming analyses. These new parametrizations are based on the na\"ive factorization hypothesis and the description of the resulting matrix elements in terms of well-known hadronic form factors, with special emphasis on the $K\pi$ scalar and vector cases. Such form factors account for two-body final state interactions which fulfill analyticity, unitarity and chiral symmetry constraints. As a result of our study, we find that the $P$-wave contribution fits nicely within the na\"ive-factorization approach, whereas the $S$-wave contribution requires complex Wilson coefficients that hint for possibly genuine three-body non-factorizable effects. Our hypothesis is further supported by the examination of $D_s^+\to K^+K^+\pi^-$ decays, where we achieve a description in overall good agreement with data., Comment: 23 pages, 8 figures; version accepted for publication in Phys.Rev.D

A short review of our recent work on amplitude parametrizations of three-body hadronic weak $B$ and $D$ decays is presented. The final states are here composed of three light mesons, namely the various charge $\pi\pi\pi$, $K\pi\pi$ and $KK\bar K$ states. These parametrizations are derived from previous calculations based on a quasi-two-body factorization approach where the two-body hadronic final state interactions are fully taken into account in terms of unitary $S$- and $P$-wave $\pi\pi$, $\pi K$ and $K \bar K$ form factors. They are an alternative to the isobar-model description and can be useful in the interpretation of CP asymmetries., Comment: 6 pages. Contribution presented at the 9th International Workshop on Charm Physics, Budker INP, Novosibirsk, Russia, May 21 to 25, 2018, submitted to EPJ Web of Conferences

We introduce parametrizations of hadronic three-body $B$ and $D$ weak decay amplitudes that can be readily implemented in experimental analyses and are a sound alternative to the simplistic and widely used sum of Breit-Wigner type amplitudes, also known as the isobar model. These parametrizations can be particularly useful in the interpretation of CP asymmetries in the Dalitz plots. They are derived from previous calculations based on a quasi-two-body factorization approach in which two-body hadronic final state interactions are fully taken into account in terms of unitary $S$- and $P$-wave $\pi\pi$, $\pi K$ and $K \bar K$ form factors. These form factors can be determined rigorously, fulfilling fundamental properties of quantum field-theory amplitudes such as analyticity and unitarity, and are in agreement with the low-energy behaviour predicted by effective theories of QCD. They are derived from sets of coupled-channel equations using $T$-matrix elements constrained by experimental meson-meson phase shifts and inelasticities, chiral symmetry and asymptotic QCD. We provide explicit amplitude expressions for the decays $B^\pm \to \pi^+ \pi^- \pi^\pm$, $B \to K \ \pi^+ \pi^-$, $B^\pm \to K^+ K^-K^\pm$, $D^+ \to \pi^- \pi^+ \pi^+ $, $D^+ \to K^- \pi^+ \ \pi^+ $, $D^0 \to K^0_S \ \pi^+\ \pi^- $, for which we have shown in previous studies that this approach is phenomenologically successful, in addition, we provide expressions for the $D^0 \to K^0_S \ K^+ K^-$ decay. Other three-body hadronic channels can be parametrized likewise., Comment: 38 pages. Extended discussions and several references added. Accepted for publication in Physical Review D

The $\eta$ transition form factor is analysed for the first time in both space- and time-like regions at low and intermediate energies in a model-independent approach through the use of rational approximants. The $\eta\rightarrow e^+e^-\gamma$ experimental data provided by the A2 Collaboration in the very low energy region of the dilelectron invariant mass distribution allows for the extraction of the most precise up-to-date slope and curvature parameters of the form factors as well as their values at zero and infinity. The impact of these new results on the mixing parameters of the $\eta$-$\eta^\prime$ system, together with the role played by renormalisation dependent effects, and on the determination of the $VP\gamma$ couplings from $V\to P\gamma$ and $P\to V\gamma$ radiative decays are also discussed., Comment: 16 pages, 17 figures; v2: additional comments, references added; mathces published version in EPJC

In a combined study of the decay spectra of $\tau^-\to K_S\pi^-\nu_\tau$ and $\tau^-\to K^-\eta\nu_\tau$ decays within a dispersive representation of the required form factors, we illustrate how the $K^*(1410)$ resonance parameters, defined through the pole position in the complex plane, can be extracted with improved precision as compared to previous studies. While we obtain a substantial improvement in the mass, the uncertainty in the width is only slightly reduced, with the findings $M_{K^{*\prime}}=1304 \pm 17\,$MeV and $\Gamma_{K^{*\prime}} = 171 \pm 62\,$MeV. Further constraints on the width could result from updated analyses of the $K\pi$ and/or $K\eta$ spectra using the full Belle-I data sample. Prospects for Belle-II are also discussed. As the $K^-\pi^0$ vector form factor enters the description of the decay $\tau^-\to K^-\eta\nu_\tau$, we are in a position to investigate isospin violations in its parameters like the form factor slopes. In this respect also making available the spectrum of the transition $\tau^-\to K^-\pi^0\nu_\tau$ would be extremely useful, as it would allow to study those isospin violations with much higher precision., Comment: 20 pages, 1figure

We measure the band strengths in the far-infrared region of interstellar ice analogs of astrophysically relevant species, such as H$_2$O, CO$_2$, CH$_3$OH, and NH$_3$, deposited at low temperature (8-10 $\mathrm{K}$), followed by warm-up, to induce amorphous-crystalline phase transitions when relevant. The spectra of pure H$_2$O, NH$_3$, and CH$_3$OH ices have been measured in the near-, mid- and far-infrared spectroscopic regions using the Interstellar Astrochemistry Chamber (ISAC) ultra-high-vacuum setup. In addition, far-infrared spectra of NH$_3$ and CO$_2$ were measured using a different set-up equipped with a bolometer detector. Band strengths in the far-infrared region were estimated using the corresponding near- and mid-infrared values as a reference. We also performed theoretical calculations of the amorphous and crystalline structures of these molecules using solid state computational programs at density functional theory (DFT) level. Vibrational assignment and mode intensities for these ices were predicted. Infrared band strengths in the 25-500 ${\mu}$m range have been determined for the considered ice samples by direct comparison in the near- and mid-infrared regions. Our values were compared to those we calculated from the literature complex index of refraction. We found differences of a factor of two between the two sets of values. The calculated far-infrared band strengths provide a benchmark for interpreting the observational data from future space telescope missions, allowing the estimation of the ice column densities., Comment: Key words. astrochemistry -- methods: laboratory: solid state -- ISM: molecules -- techniques: spectroscopic -- infrared: ISM

The mini-proceedings of the Light Meson Dynamics Workshop held in Mainz from February 10th to 12th, 2014, are presented. The web page of the conference, which contains all talks, can be found at https://indico.cern.ch/event/287442/overview ., Comment: 46 pages, 17 contributions. Editors: W. Gradl, P. Masjuan, M. Ostrick, and S. Scherer

We have studied the $\tau^-\to K^-\eta^{(\prime)}\nu_\tau$ decays within Chiral Perturbation Theory including resonances as explicit degrees of freedom. We have considered three different form factors according to treatment of final-state interactions. In increasing degree of soundness: Breit-Wigner, exponential resummation and dispersive representation. We find that although the first one fails in accounting for the data on the $K\eta$ mode, the other two approaches provide good fits to them which are sensitive to the $K^\star(1410)$ pole parameters, that are determined to be $M_{K^{\star\prime}}\,=\,(1330^{+27}_{-41})$ MeV and $\Gamma_{K^{\star\prime}}\,=\,(217^{+68}_{-122})$ MeV. These values are competitive with the standard determination from $\tau^-\to(K\pi)^-\nu_\tau$ decays. The corresponding predictions for the $\tau^-\to K^-\eta^{\prime}\nu_\tau$ channel respect the current upper bound and hint to the discovery of this decay mode in the near future., Comment: 26 pages, 6 tables, 4 figures. Minor changes to match published version. Journal reference and DOI added

This report describes the scientific aims and potentials as well as the preliminary technical design of IRIDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity 'particle factory', based on a combination of a high duty cycle radio-frequency superconducting electron linac and of high energy lasers. Conceived to provide unique research possibilities for particle physics, for condensed matter physics, chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. IRIDE will contribute to open new avenues of discoveries and to address most important riddles: What does matter consist of? What is the structure of proteins that have a fundamental role in life processes? What can we learn from protein structure to improve the treatment of diseases and to design more efficient drugs? But also how does an electronic chip behave under the effect of radiations? How can the heat flow in a large heat exchanger be optimized? The scientific potential of IRIDE is far reaching and justifies the construction of such a large facility in Italy in synergy with the national research institutes and companies and in the framework of the European and international research. It will impact also on R&D work for ILC, FEL, and will be complementarity to other large scale accelerator projects. IRIDE is also intended to be realized in subsequent stages of development depending on the assigned priorities., Comment: 270 pages

The \eta and \eta' transition form factors in the space-like region are analyzed at low and intermediate energies in a model-independent way through the use of rational approximants. The slope and curvature parameters of the form factors as well as their values at zero and infinity are extracted from experimental data. The impact of these results on the mixing parameters of the \eta-\eta' system and the pseudoscalar-exchange contributions to the hadronic light-by-light scattering part of the anomalous magnetic moment are also discussed., Comment: 15 pages, 11 figures. v2: references added and minor typos corrected. v3: more references added and a new figure comparing different slope determinations is included. Matches the published version in PRD

Dispersive representations of the Kpi vector and scalar form factors are used to fit the spectrum of tau ---> K pi nu_tau obtained by the Belle collaboration incorporating constraints from results for K_l3 decays. The slope and curvature of the vector form factor are obtained directly from the data through the use of a three-times-subtracted dispersion relation. We find $\lambda_+'=(25.49 \pm 0.31) \times 10^{-3}$ and $\lambda_+"= (12.22 \pm 0.14) \times 10^{-4}$. From the pole position on the second Riemann sheet the mass and width of the $K^*(892)^{\pm}$ are found to be $m_{K^*(892)^\pm}=892.0\pm 0.5$~MeV and $\Gamma_{K^*(892)^\pm}=46.5\pm 1.1$~MeV. The phase-space integrals needed for K_l3 decays are calculated as well. Furthermore, the Kpi isospin-1/2 P-wave threshold parameters are derived from the phase of the vector form factor. For the scattering length and the effective range we find respectively $a_{1}^{1/2}\,= ( 0.166\pm 0.004)\,m_\pi^{-3}$ and $b_{1}^{1/2}\,=( 0.258\pm 0.009)\,m_\pi^{-5}$., Comment: 22 pages, 4 figures

We present a model for the decay $D^+\to K^-\pi^+\pi^+$. The weak interaction part of this reaction is described using the effective weak Hamiltonian in the factorisation approach. Hadronic final state interactions are taken into account through the $K\pi$ scalar and vector form factors fulfilling analyticity, unitarity and chiral symmetry constraints. Allowing for a global phase difference between the $S$ and $P$ waves of $-65^\circ$, the Dalitz plot of the $D^+\to K^-\pi^+\pi^+$ decay, the $K\pi$ invariant mass spectra and the total branching ratio due to $S$-wave interactions are well reproduced., Comment: 5 pages, uses aipproc style. Talk presented by R. Escribano at the XIII International Conference on Hadron Spectroscopy (HADRON09), Florida State University (Tallahassee), USA, 29.11-4.12.2009

Investigation at a $\phi$--factory can shed light on several debated issues in particle physics. We discuss: i) recent theoretical development and experimental progress in kaon physics relevant for the Standard Model tests in the flavor sector, ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled kaon states, iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and eta/eta$^\prime$ mesons, iv) the contribution to understand the nature of light scalar mesons, and v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We also report on the $e^+ e^-$ physics in the continuum with the measurements of (multi)hadronic cross sections and the study of gamma gamma processes., Comment: 60 pages, 41 figures; added affiliation for one of the authors; added reference to section 6

We present a model for the decay D+ --> K- pi+ pi+. The weak interaction part of this reaction is described using the effective weak Hamiltonian in the factorisation approach. Hadronic final state interactions are taken into account through the Kpi scalar and vector form factors fulfilling analyticity, unitarity and chiral symmetry constraints. The model has only two free parameters that are fixed from experimental branching ratios. We show that the modulus and phase of the S wave thus obtained agree nicely with experiment up to 1.55 GeV. We perform Monte Carlo simulations to compare the predicted Dalitz plot with experimental analyses. Allowing for a global phase difference between the S and P waves of -65 degrees, the Dalitz plot of the D+ --> K- pi+ pi+ decay, the Kpi invariant mass spectra and the total branching ratio due to S-wave interactions are well reproduced., Comment: 24 pages, 4 figures, REVTeX style. A discussion on the isospin 2 component has been included. Two references added. Published in Phys. Rev. D

The $\eta$-$\eta^\prime$ pseudoscalar mixing angle and the gluonium content of the $\eta^\prime$ meson are deduced from an updated phenomenological analysis of $J/\psi$ decays into a vector and a pseudoscalar meson. The values for the mixing angle and the gluonic content of the $\eta^\prime$ wave function are $\phi_P=(44.5\pm 4.3)^\circ$ and $Z^2_{\eta^\prime}=0.28\pm 0.21$, respectively., Comment: 5 pages, uses espcrc2 style. Talk presented at the International Workshop on e+e- collisions from Phi to Psi (PHIPSI08), Laboratori Nazionali di Frascati (Rome), Italy, 7-10 April 2008

The $\eta$-$\eta^\prime$ pseudoscalar mixing angle and the gluonium content of the $\eta^\prime$ meson are deduced from an updated phenomenological analysis of $J/\psi$ decays into a vector and a pseudoscalar meson. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be $\phi_P=(40.7\pm 2.3)^\circ$. In presence of gluonium, the values for the mixing angle and the gluonic content of the $\eta^\prime$ wave function are $\phi_P=(44.6\pm 4.4)^\circ$ and $Z^2_{\eta^\prime}=0.29^{+0.18}_{-0.26}$, respectively. The newly reported values of $B(J/\psi\to\rho\pi)$ by the BABAR and BES Collaborations are crucial to get a consistent description of data., Comment: 7 pages, 1 figure, uses svjour style. Comments on the relationship between J/psi to VP and V to Pgamma decays and on the neglected contributions together with an asymmetric treatment of errors are included

The radiative decays $V\to S\gamma$ and $S\to V\gamma$ with $V=\rho, \omega, \phi$ and $S=a_0, \sigma, f_0$ are calculated within the framework of the Linear Sigma Model. Current experimental data on the $\phi\to f_0\gamma$ and $\rho\to\sigma\gamma$ branching ratios and the ratio $\Gamma(\phi\to f_0\gamma)/\Gamma(\phi\to a_0\gamma)$ are satisfactorily accommodated in our approach. We also estimate the decay widths of the $f_0,a_0\to\rho\gamma,\omega\gamma$ transitions. All the processes considered are of interest for ongoing experimental programs in Frascati, J\"ulich and Novosibirsk., Comment: A comment on vector meson loops added. 2 references added. Typos corrected. Accepted for publication in Physics Letters B

A phenomenological analysis of radiative $V\to P\gamma$ and $P\to V\gamma$ decays is performed with the purpose of determining the gluonic content of the $\eta$ and $\eta^\prime$ wave functions. Our results show that within our model there is no evidence for a gluonium contribution in the $\eta$, $Z_\eta^2=0.00\pm 0.12$, or the $\eta^\prime$, $Z_{\eta^\prime}^2=0.04\pm 0.09$. In terms of a mixing angle description this corresponds to $\phi_P=(41.4\pm 1.3)^\circ$ and $|\phi_{\eta^\prime G}|=(12\pm 13)^\circ$. In addition, the $\eta$-$\eta^\prime$ mixing angle is found to be $\phi_P=(41.5\pm 1.2)^\circ$ if we don't allow for a gluonium component., Comment: 16 pages, 3 figures, JHEP style. First part of data fitting changed, conclusions not modified

A two mixing angle description of the pseudoscalar decay constants associated to the $\eta$-$\eta^\prime$ system is used to parametrize the theoretical amplitudes of the radiative decays $(\eta,\eta^\prime)\to\gamma\gamma$ and the coupling constants $g_{V(\eta,\eta^\prime)\gamma}$ with $V=\rho,\omega,\phi$. The parametrization is performed in both the ``octet-singlet'' basis and the ``quark-flavour'' basis. An excellent agreement with the most recent experimental data is achieved. Our analysis reveals that at the present experimental accuracy the two mixing angles differ significantly in the former basis but not in the latter, in accordance with the expectations of large $N_c$ Chiral Perturbation Theory where the difference between the two mixing angles are due to a $SU(3)_f$-breaking effect and a violation of the OZI rule respectively., Comment: 4 pages, uses PoS style. Contribution to the proceedings of the International Europhysics Conference on High Energy Physics (HEP2005), Lisboa, Portugal, 21-27 July 2005

A phenomenological analysis of various decay processes is performed in order to test the large $N_c$ Chiral Perturbation Theory predictions for the octet and singlet pseudoscalar decay constants and mixing angles. The results obtained hint at a disagreement with the expectations of this theoretical framework although the statistical significance is still limited., Comment: 7 pages, uses appolb style. Talk presented at the PHOTON2005 International Conference on the Structure and Interactions of the Photon, Warsaw, Poland, 31.8-4.9.2005

An analysis of various radiative $VP\gamma$ decays is performed using the two mixing angle description of the $\eta$-$\eta^\prime$ system. The agreement is excellent. Our results are expressed both in the ``octet-singlet'' and in the ``quark-flavour'' basis. It turns out that at the present experimental accuracy, the two angles are significantly different in the former, but not in the latter basis., Comment: 4 pages, uses espcrc2 style. Talk presented at the 12th International High-Energy Physics Conference in Quantum Chromodynamics (QCD 2005), Montpellier, France, 4-8 July 2005

A test on quantum mechanics proposed long ago by Karl Popper is reconsidered with further detail and new insight. An ambiguity in the proposal, which turns out to be essential in order to make the test conclusive, is identified and taken into account for the first time. Its implications for recently performed photon experiments [such as in D. V. Strekalov \textit{et al.}, Phys. Rev.\ Lett. {\bf 74}, 3600 (1995)] are briefly analyzed., Comment: 4 pages, 1 figure, REVTeX style

A test of quantum mechanics proposed by K. Popper and dealing with two-particle entangled states emitted from a fixed source has been criticized by several authors. Some of them claim that the test becomes inconclusive once all the quantum aspects of the source are considered. Moreover, another criticism states that the predictions attributed to quantum mechanics in Popper's analysis are untenable. We reconsider these criticisms and show that, to a large extend, the `falsifiability' potential of the test remains unaffected., Comment: 7 pages, uses svmult style. Contribution to the book dedicated to Prof. Alberto Galindo, on occasion of his seventieth birthday

Recent proposals to test Bell's inequalities with entangled pairs of pseudoscalar mesons are reviewed. This includes pairs of neutral kaons or B-mesons and offers some hope to close both the locality and the detection loopholes. Specific difficulties, however, appear thus invalidating most of those proposals. The best option requires the use of kaon regeneration effects and could lead to a successful test if moderate kaon detection efficiencies are achieved., Comment: 19 pages, 1 figure. Contribution to the Festschrift in honor of Prof. E. Santos for his 70th birthday

An analysis of various decay processes is performed using the two mixing angle description of the $\eta$-$\eta^\prime$ system, incorporating the link to the gluonic sector through anomalies. The agreement is excellent. For comparison with previous works, our results are expressed both in the ``octet-singlet'' and in the ``quark-flavour'' basis. It turns out that at the present experimental accuracy, the two angles are significantly different in the former, but not in the latter basis. The implications of our analysis for the Large $N_c$ $\chi$PT predictions are also discussed., Comment: 15 pages, JHEP style. Comments on the VMD description of the VPgamma decays, the error correlations,the scale dependence of f0, and the implications of the analysis for Large Nc ChpT are included

We analyse the recent claim that a violation of a Bell's inequality has been observed in the $B$--meson system [A. Go, {\em Journal of Modern Optics} {\bf 51} (2004) 991]. The results of this experiment are a convincing proof of quantum entanglement in $B$--meson pairs similar to that shown by polarization entangled photon pairs. However, we conclude that the tested inequality is not a genuine Bell's inequality and thus cannot discriminate between quantum mechanics and local realistic approaches., Comment: 5 pages

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 publication

A consistent description of $\sigma(500)$ meson effects in $\rho^0\to\pi^0\pi^0\gamma$ and $\pi^+\pi^-\gamma$ decays is proposed in terms of reasonably simple amplitudes which reproduce the expected chiral-loop behaviour for large $m_{\sigma}$ values. For the neutral case, in addition to the well known $\omega$ exchange, there is an important contribution from the $\sigma(500)$ meson that is in agreement with recent experimental data. For the charged case, where the dominant contribution comes from bremsstrahlung, the effects of the $\sigma(500)$ meson are relevant only at high values of the photon energy and compatible with present data. A combined analysis of both processes with moderately improved experimental information should contribute decisively to clarify the status of this controversial $\sigma(500)$ meson., Comment: 11 pages, 3 figures, JHEP style. A comment on the O(p^4) ChPT calculation of the four-pseudoscalar amplitudes is included; a new discussion on the effects of our parametrization on the I=J=0 pi-pi phaseshift is also included. Final version accepted for publication

The complementarity between Chiral Perturbation Theory and the Linear Sigma Model is exploited to study $\pi^0\pi^0$ production in $\phi$ radiative decays, where the effects of the $f_0(980)$ scalar resonance, and those of its more controversial $\sigma(500)$ partner, should become manifest via the $\phi\to K^+ K^- (\gamma)\to\pi^0\pi^0\gamma $ decay chain. The recently reported data on $\phi\to\pi^0\pi^0\gamma$ coming from the VEPP-2M $e^+ e^-$ collider in Novosibirsk and the DA$\Phi$NE $\phi$-factory in Frascati can be reasonably described in our approach, which we propose as a promising first step towards more detailed analyses. The $f_0(980)$ contribution, which appears as a moderately narrow peak at the high part of the dipion mass spectrum, can be interpreted as the isoscalar member of the scalar nonet with a large $f_0 K\bar{K}$ coupling and an $f_0\pi\pi$ coupling suppressed by almost ideal $\sigma$-$f_0$ mixing. Indeed, the mixing angle in the flavour basis is found to be $\phi_{S}\approx -6^\circ$, if the $f_0$-propagator is approximated by a simple Breit-Wigner, or $\phi_{S}\approx -9^\circ$, if an improved two-channel analysis is performed. The $\sigma(500)$ resonance, which is then strongly coupled to pion pairs, yields a tiny contribution because, in our approach, its coupling to kaon pairs is proportional to $m^2_\sigma-m^2_K$ and thus quite small., Comment: 18 pages, 4 figures; new treatment of the f0 propagator added and Comments on previous work corrected

Using the pole approach we determine the mass and width of the $f_0(980)$; in particular, we analyze the possibility that two nearby poles are associated to it. We restrict our analysis to a neighborhood of the resonance, using $\pi\pi$ data for the phase shift and inelasticity, and the invariant mass spectrum of the $J/\psi\to\phi\pi\pi, \phi K\bar K$ decays. The formalism we use is based on unitarity and a generalized version of the Breit-Wigner parameterization. We find that a single pole describes the $f_0(980)$, the precise position depending upon the $\pi\pi$ data used. As a byproduct, values for the $g_{f_0\pi\pi}$ and $g_{f_0K\bar K}$ coupling constants are obtained., Comment: 18 pages, 2 figures. A new analysis including the latest pi-pi phase shift data is performed. To be published in Eur. Phys. J. C

We discuss the gravitational lensing of neutrinos by astrophysical objects. Unlike photons, neutrinos can cross a stellar core; as a result, the lens quality improves. We also estimate the depletion of the neutrino flux after crossing a massive object and the signal amplification expected. While Uranians alone would benefit from this effect in the Sun, similar effects could be considered for binary systems., Comment: 15 pages, 4 figures, to be published in Phys. Lett. B

The complementarity between Chiral Perturbation Theory and the Linear Sigma Model in the scalar channel is exploited to study $\pi^0\pi^0$ production in $\rho$ and $\omega$ radiative decays, where the effects of a low mass scalar resonance $\sigma(500)$ should manifest. The recently reported data on $\rho\to\pi^0\pi^0\gamma$ seem to require the contribution of a low mass and moderately narrow $\sigma(500)$. The properties of this controversial state could be fixed by improving the accuracy of these measurements. Data on $\omega\to\pi^0\pi^0\gamma$ can also be accommodated in our framework, but are much less sensitive to the $\sigma(500)$ properties., Comment: 17 pages, 4 figures

A value for the $\eta$-$\eta^\prime$ mixing angle is extracted from the data on $VP\gamma$ transitions using simple quark-model ideas. The set of data covers {\it all} possible radiative transitions between the pseudoscalar and vector meson nonets. Two main ingredients of the model are the introduction of flavour-dependent overlaps for the various $q\bar{q}$ wave functions and the use of the quark-flavour basis to describe the $\eta$-$\eta^\prime$ system. In this basis the mixing angle is found to be $\phi_P=(37.7\pm 2.4)^\circ$., Comment: 10 pages

A prediction for the contributions of chiral loops and the L$\sigma$M model to the radiative $\phi\to\pi^0\eta\gamma$ decay mode is presented. The L$\sigma$M is used as an appropriate framework for describing the pole effects of the $a_0(980)$ scalar resonance. As a result, a better agreement with present available data is achieved for the higher part of the $\pi^0\eta$ invariant mass spectrum. For the branching ratio, a value of $B(\phi\to\pi^0\eta\gamma)=(0.75$--$0.95)\times 10^{-4}$ is found., Comment: 10 pages, 2 figures. Talk given at the Hadron Structure'2000 Conference, Stara Lesna, High Tatras Mountains, Slovakia, 2-7 October 2000

The radiative $\phi\to\pi^0\eta\gamma$ decay is discussed emphasizing the effects of the $a_0$(980) scalar resonance which dominates the high values of the $\pi^0\eta$ invariant mass spectrum. In its lowest part, the proposed amplitude coincides with the reliable and ChPT-inspired contribution coming from chiral loops. The $a_0$(980) resonance is then incorporated exploiting the complementarity between ChPT and the linear sigma model for this channel. The recently reported experimental invariant mass distribution and branching ratio can be satisfactorily accommodated in our framework. For the latter, a value of $B(\phi\to\pi^0\eta\gamma)$ in the range $(0.75$--$0.95)\times 10^{-4}$ is predicted., Comment: 16 pages, 3 figures

The ratio Phi->K+K-/K0K0bar is discussed and its present experimental value is compared with theoretical expectations. A difference larger than two standard deviations is observed. We critically examine a number of mechanisms that could account for this discrepancy, which remains unexplained. Measurements at DAPHNE at the level of the per mille accuracy can clarify whether there exist any anomaly., Comment: 16 pages

We study the temperature dependence of the eta and eta' meson masses within the framework of U(3)_L x U(3)_R chiral perturbation theory, up to next-to-leading order in a simultaneous expansion in momenta, quark masses and number of colours. We find that both masses decrease at low temperatures, but only very slightly. We analyze higher order corrections and argue that large N_c suggests a discontinuous drop of M_eta' at the critical temperature of deconfinement T_c, consistent with a first order transition to a phase with approximate U(1)_A symmetry., Comment: 21 pages, 6 figures. 2 footnotes added, 1 reference changed and 1 typo corrected. To be published in Phys. Rev. D

We study the lensing of neutrinos by astrophysical objects. At the difference of photons, neutrinos can cross a stellar core; as a result the lens quality improves. While Saturnians alone would benefit from this effect in the Sun, similar effects could be considered for binary systems., Comment: 34 pages, 8 figures included, uses epsfig

A phenomenological analysis on various decay processes is performed using an energy-dependent $\eta-\eta'$ mixing angle scheme. Special attention is given to the radiative couplings between lowest-lying vector and pseudoscalar mesons. The agreement between our predictions and the experimental values is remarkable. This analysis opens a connection to two-angle fits in the $\eta-\eta'$ sector., Comment: 13 pages. Introduction slightly modified. A second Table added. Conclusions remain unchanged

Central pseudoscalar production in $pp$ scattering is suppressed at small values of $Q_\perp$. Such a behavior is expected if the production occurs through the fusion of two vectors. We argue that an extension of the experiment could probe the gluon contribution to the proton spin., Comment: 6 pages. Talk given at the Quarks'98 conference in Suzdal, Russia, May 1998

The presence of neutrinos from Boron decay in the flux observed on Earth is attested by the observation of their energy spectrum. Possible distortions of the spectrum investigated in current detectors are often interpreted in terms of evidence in favour or against various schemes of neutrino oscillations. We stress here that a distortion of the spectrum at high energies could also result from an increase in the ratio of neutrinos originating from ($^3$He+p) and $^8$B reactions. While a $^8$B neutrino depletion would contribute to this effect, an increase in the Hep contribution seems also needed to reproduce the preliminary data., Comment: 8 pages, 2 figures; abstract and introduction rewritten to match the conclusions better

Central pseudoscalar production in $pp$ scattering is suppressed at small values of $Q_\perp$, where $Q$ is defined as the difference between the momenta transferred from the two protons. Such a behaviour is expected if the production occurs through the fusion of two vectors. Photon exchange could provide the dominant contribution at low transferred momenta, but we argue that an extension of the experiment could probe the gluon contribution to the proton spin., Comment: 12 pages, 2 figures and 3 tables, uses epsf.sty. Added references and tables. Minor changes included

The value of the $\eta - \eta'$ mixing angle $\theta_P$ is phenomenologically deduced from a rather exhaustive and up-to-date analysis of data including strong decays of tensor and higher-spin mesons, electromagnetic decays of vector and pseudoscalar mesons, $J/\psi$ decays into a vector and a pseudoscalar meson, and other transitions. A value of $\theta_P$ between $-17^\circ$ and $-13^\circ$ is consistent with all the present experimental evidence and the average $\theta_P=-15.5^\circ\pm 1.3^\circ$ seems to be favoured., Comment: 17 pages, LaTeX. 2 references added, some comments on Chiral Perturbation Theory

The octet-singlet mixing angle $\theta_P$ in the pseudoscalar meson nonet is deduced from the rich set of accurate data on $J/\psi$ decays into a vector and a pseudoscalar meson. Corrections due to non-ideal $\omega$-$\phi$ mixing have been included for the first time and turn out to be crucial to find $\theta_P = -16.9 \pm 1.7$ degrees, which is appreciably less negative than previous results coming from similar analyses., Comment: 9 pages, LaTeX, full postscript file available via anonymous ftp at ftp://ftp.ifae.es/preprint/ft/uabft412.ps