George Rupp | Faculdade de Arquitectura da Universidade de Lisboa (original) (raw)

Papers by George Rupp

arXiv (Cornell University), Jul 16, 2017

arXiv (Cornell University), Aug 29, 2022

arXiv (Cornell University), Feb 17, 2022

Progress in Particle and Nuclear Physics, Mar 1, 2021

arXiv (Cornell University), Jun 9, 2006

arXiv (Cornell University), May 13, 2016

Quark models taking into account the dynamical effects of hadronic decay often produce very diffe... more Quark models taking into account the dynamical effects of hadronic decay often produce very different predictions for mass shifts in the hadron spectrum. The consequences for meson spectroscopy can be dramatic and completely obscure the underlying confining force. Recent unquenched lattice calculations of mesonic resonances that also include meson-meson interpolators provide a touchstone for such models, despite the present limitations in applicability. On the experimental side, the ρ(770) meson and its several observed radial recurrences are a fertile testing ground for both quark models and lattice computations. Here we apply a unitarised quark model that has been successful in the description of many enigmatic mesons to these vector ρ resonances and the corresponding P-wave ππ phase shifts. This work is in progress, with encouraging preliminary results.

arXiv (Cornell University), Oct 4, 2015

The ρ(770) vector resonance, its radial recurrences, and the corresponding Pwave ππ phase shifts ... more The ρ(770) vector resonance, its radial recurrences, and the corresponding Pwave ππ phase shifts are investigated in an unquenched quark model with all classes of relevant decay channels included, viz. pseudoscalar-pseudoscalar, vectorpseudoscalar, vector-vector, vector-scalar, axialvector-pseudoscalar, and axialvectorvector, totalling 26 channels. Two of the few model parameters are fixed at previously used values, whereas the other three are adjusted to the ρ(770) resonance and the lower P-wave ππ phases. Preliminary results indicate the model's capacity to reproduce these phases as well as the ρ mass and width. However, at higher energies the phase shifts tend to rise too sharply. A possible remedy is an extension of the model so as to handle resonances in the final states for most of the included decay channels. Work in progress.

arXiv (Cornell University), Nov 3, 2021

Acta Physica Polonica, 2016

Besides general features of the Resonance Spectrum Expansion for twoboson mass distributions, exp... more Besides general features of the Resonance Spectrum Expansion for twoboson mass distributions, experimental results are discussed. Furthermore, E(38 MeV) and Z(57.5 GeV) are highlighted.

arXiv (Cornell University), Apr 14, 2019

An unambiguous definition of meson resonance masses requires a description of the associated phas... more An unambiguous definition of meson resonance masses requires a description of the associated phase shifts in terms of a manifestly unitary Smatrix and its complex poles. However, the commonly used Breit-Wigner (BW) parametrisations can lead to appreciable deviations. We demonstrate this for a simple elastic resonance, viz. ρ(770), whose pole and BW masses turn out to differ by almost 5 MeV. In the case of the very broad f 0 (500) and K 0 (700) scalar mesons, the discrepancies are shown to become much larger, while also putting question marks at the listed PDG BW masses and widths. Furthermore, some results are reviewed of a manifestly unitary model for meson spectroscopy, which highlight the potentially huge deviations from static model predictions. Finally, a related unitary model for production amplitudes is shown to explain several meson enhancements as non-resonant threshold effects, with profound implications for spectroscopy.

Acta Physica Polonica, 2017

Besides the unitarity and symmetry requirements for a multi-resonance scattering amplitude, sever... more Besides the unitarity and symmetry requirements for a multi-resonance scattering amplitude, several other natural conditions can easily exclude unrealistic proposals. In particular, the behaviour of singularities under the variation of model parameters yields important information. We discuss how resonance poles should move in the complex-energy plane when coupling constants and masses are varied, how resonances above threshold can turn into bound states below threshold, and how the light-quark spectrum can be turned into the spectrum of heavy quarks, with one and the same analytic expression for the scattering amplitude. Moreover, it is shown that perturbative approximations usually do not satisfy these natural conditions.

Acta Physica Polonica, 2015

In this talk we review the limitations of including meson loops as perturbative corrections in a ... more In this talk we review the limitations of including meson loops as perturbative corrections in a solvable quark model. We first discuss meson-meson scattering within a formalism which treats confined quark pairs and mesons on an equal footing. The interaction between the mesons proceeds through s-channel meson-exchange diagrams. Next, we develop a perturbative expansion of the model, and show that the resonance poles found in such a treatment, even by accounting for contributions up to fourth order, do not coincide with those obtained with the full model. We conclude that the resonance predictions based on perturbative approximations in quark models are not reliable, especially in those cases where the coupling to the scattering channels is large.

arXiv (Cornell University), Oct 4, 2003

Data indicate that ∆I = 3/2 transitions account for 4.5-4.7% of both CP conserving and CP violati... more Data indicate that ∆I = 3/2 transitions account for 4.5-4.7% of both CP conserving and CP violating K → 2π decays, as well as CP conserving radiative K → ππγ processes. Observed K → ππγ/ππ branching ratios are shown to scale near α/π or α/2π. The K L-K S mixing angle φ and the semileptonic weak-rate asymmetry δ are reviewed, and theory is shown to be consistent with data. Also, K → 2π ∆I = 1/2 dominance is studied in the context of the chiral constituent quark model, displaying again excellent agreement with data. Finally, indirect and direct kaon CP violation (CPV) are successfully described in the framework of photon-mediated quark-loop graphs. This suggests that kaon CPV can be understood via second-order weak transitions, radiatively corrected.

arXiv (Cornell University), Jun 3, 1998

It is shown that the incomplete scalar meson nonets found by Törnqvist [1] and Törnqvist & Roos [... more It is shown that the incomplete scalar meson nonets found by Törnqvist [1] and Törnqvist & Roos [2], employing a new version of the Helsinki unitarised quark model, should in fact be complete, including an as yet unconfirmed light K * 0 below 1 GeV (old κ) and the established f 0 (1500). A detailed comparison is presented with the predictions of the Nijmegen unitarised meson model, in which two complete scalar nonets show up below 1.5 GeV [3]. The reason for the flavour-nonet breaking found in Refs. [1, 2] we argue to originate in the use of coupling constants for the three-meson vertex which are not independent of flavour. Also some statements made in Ref. [1] are critically reviewed.

Acta Physica Polonica, 2018

Half a century of work on the light scalar mesons f 0 (500), f 0 (980), K ⋆ 0 (700), and a 0 (980... more Half a century of work on the light scalar mesons f 0 (500), f 0 (980), K ⋆ 0 (700), and a 0 (980) is briefly reviewed. After summarising all light scalar candidates in the Review of Particle Physics since 1963, a selection of different theoretical and phenomenological descriptions is presented, including pure meson-meson models, a tetraquark construction, unitarised quarkmeson models, unitarised effective chiral approaches, and a very recent lattice-QCD simulation.

Journal of Physics: Conference Series, 2019

New enhancements in the charmonium and bottomonium spectra observed since 2003 are very briefly r... more New enhancements in the charmonium and bottomonium spectra observed since 2003 are very briefly reviewed. Special attention is paid to χc1(3872) (formerly X(3872)) owing to its remarkable proximity to theD 0 D 0 threshold, which allows modelling as a quasibound axial-vector cc state with a largeD 0 D 0 admixture. In contrast, the interpretation of many other charmonium-like and bottomonium-like states is still very controversial and some may not even correspond to genuine resonances. Accordingly, several entries in the PDG tables have been wildly changing over the years. Three representative states are reviewed here as non-resonant enhancements due to threshold effects, viz. ψ(4260), ψ(4660), and Υ(10580).

Acta Physica Polonica B Proceedings Supplement, 2017

Mesons with masses below their lowest OZI-allowed strong-decay thresholds have very small widths.... more Mesons with masses below their lowest OZI-allowed strong-decay thresholds have very small widths. Thus, it is usually believed that they can be safely treated as pure quark-antiquark bound states in spectroscopy models. However, unitarised and coupled-channel models from decades ago already indicated that this may not be the case, owing to significant virtual meson-loop contributions. Recent unquenched lattice calculations that include two-meson interpolators besides the usual qq ones confirm the latter conclusion, in particular for the enigmatic narrow D s0 (2317), D s1 (2460), and X(3872) states. Here, we briefly review several predictions of some old and new quark models that go beyond the static description of mesons, also in comparison with up-to-date lattice results.

AIP Conference Proceedings, 2008

A panel discussion on scalar mesons was held with the participation of David Bugg, Yulia Kalashni... more A panel discussion on scalar mesons was held with the participation of David Bugg, Yulia Kalashnikova, Keh-Fei Liu, Michael Scadron, the author, and members of the audience. Some introductory remarks are noted here.

Physical Review D, 1983

A potential model for mesons is presented, which combines quark confinement and strong decay in a... more A potential model for mesons is presented, which combines quark confinement and strong decay in a realistic approach. The multichannel Schrodinger formalism is employed to describe a system of one or more permanently closed quark-antiquark channels in interaction with several two-meson channels. For the potential in the qq channels a harmonic oscillator with constant frequency is taken. As for the meson channels only Okubo-Zweig-Iizuka-rule-allowed decays into two mesons of the pseudoscalar or vector type are considered. Final-state interactions between these mesons are not yet taken into account. The communication between confined and free channels is supposed to take place via the 'I'0 mechanism, for which a locally approximated transition potential is derived. In order to obtain an analytic solution for the S matrix, the transition potential is treated by using a multi-5-shell method. Kinematically relativistic corrections and color splitting allow a fairly successful treatment of pseudoscalar as well as vector mesons for all quark flavors. The results are confronted with the data and discussed.

Physical Review D

In a recent paper by Gao et al. [Phys. Rev. D 105, 094002 (2022).], S-wave ππ scattering phase sh... more In a recent paper by Gao et al. [Phys. Rev. D 105, 094002 (2022).], S-wave ππ scattering phase shifts obtained in a lattice-QCD calculation are analyzed using dispersive S-matrix methods. We question the reliability of the conclusion from this analysis that, for a pion mass of 391 MeV, the lattice phases favor the presence of both a σ-meson bound state and a nearby virtual state. Our main criticism concerns the neglect of the S-wave KK channel, which was considered alongside additional ss interpolating fields in the lattice computation used by the authors of Gao et al. and also in typical coupled-channel models. As an illustration, some results from such a recent model are presented as well. Concluding remarks concern possible improvements of the analysis in Gao et al. as well as further model tests.

arXiv (Cornell University), Jul 16, 2017

arXiv (Cornell University), Aug 29, 2022

arXiv (Cornell University), Feb 17, 2022

Progress in Particle and Nuclear Physics, Mar 1, 2021

arXiv (Cornell University), Jun 9, 2006

arXiv (Cornell University), May 13, 2016

Quark models taking into account the dynamical effects of hadronic decay often produce very diffe... more Quark models taking into account the dynamical effects of hadronic decay often produce very different predictions for mass shifts in the hadron spectrum. The consequences for meson spectroscopy can be dramatic and completely obscure the underlying confining force. Recent unquenched lattice calculations of mesonic resonances that also include meson-meson interpolators provide a touchstone for such models, despite the present limitations in applicability. On the experimental side, the ρ(770) meson and its several observed radial recurrences are a fertile testing ground for both quark models and lattice computations. Here we apply a unitarised quark model that has been successful in the description of many enigmatic mesons to these vector ρ resonances and the corresponding P-wave ππ phase shifts. This work is in progress, with encouraging preliminary results.

arXiv (Cornell University), Oct 4, 2015

The ρ(770) vector resonance, its radial recurrences, and the corresponding Pwave ππ phase shifts ... more The ρ(770) vector resonance, its radial recurrences, and the corresponding Pwave ππ phase shifts are investigated in an unquenched quark model with all classes of relevant decay channels included, viz. pseudoscalar-pseudoscalar, vectorpseudoscalar, vector-vector, vector-scalar, axialvector-pseudoscalar, and axialvectorvector, totalling 26 channels. Two of the few model parameters are fixed at previously used values, whereas the other three are adjusted to the ρ(770) resonance and the lower P-wave ππ phases. Preliminary results indicate the model's capacity to reproduce these phases as well as the ρ mass and width. However, at higher energies the phase shifts tend to rise too sharply. A possible remedy is an extension of the model so as to handle resonances in the final states for most of the included decay channels. Work in progress.

arXiv (Cornell University), Nov 3, 2021

Acta Physica Polonica, 2016

Besides general features of the Resonance Spectrum Expansion for twoboson mass distributions, exp... more Besides general features of the Resonance Spectrum Expansion for twoboson mass distributions, experimental results are discussed. Furthermore, E(38 MeV) and Z(57.5 GeV) are highlighted.

arXiv (Cornell University), Apr 14, 2019

An unambiguous definition of meson resonance masses requires a description of the associated phas... more An unambiguous definition of meson resonance masses requires a description of the associated phase shifts in terms of a manifestly unitary Smatrix and its complex poles. However, the commonly used Breit-Wigner (BW) parametrisations can lead to appreciable deviations. We demonstrate this for a simple elastic resonance, viz. ρ(770), whose pole and BW masses turn out to differ by almost 5 MeV. In the case of the very broad f 0 (500) and K 0 (700) scalar mesons, the discrepancies are shown to become much larger, while also putting question marks at the listed PDG BW masses and widths. Furthermore, some results are reviewed of a manifestly unitary model for meson spectroscopy, which highlight the potentially huge deviations from static model predictions. Finally, a related unitary model for production amplitudes is shown to explain several meson enhancements as non-resonant threshold effects, with profound implications for spectroscopy.

Acta Physica Polonica, 2017

Besides the unitarity and symmetry requirements for a multi-resonance scattering amplitude, sever... more Besides the unitarity and symmetry requirements for a multi-resonance scattering amplitude, several other natural conditions can easily exclude unrealistic proposals. In particular, the behaviour of singularities under the variation of model parameters yields important information. We discuss how resonance poles should move in the complex-energy plane when coupling constants and masses are varied, how resonances above threshold can turn into bound states below threshold, and how the light-quark spectrum can be turned into the spectrum of heavy quarks, with one and the same analytic expression for the scattering amplitude. Moreover, it is shown that perturbative approximations usually do not satisfy these natural conditions.

Acta Physica Polonica, 2015

In this talk we review the limitations of including meson loops as perturbative corrections in a ... more In this talk we review the limitations of including meson loops as perturbative corrections in a solvable quark model. We first discuss meson-meson scattering within a formalism which treats confined quark pairs and mesons on an equal footing. The interaction between the mesons proceeds through s-channel meson-exchange diagrams. Next, we develop a perturbative expansion of the model, and show that the resonance poles found in such a treatment, even by accounting for contributions up to fourth order, do not coincide with those obtained with the full model. We conclude that the resonance predictions based on perturbative approximations in quark models are not reliable, especially in those cases where the coupling to the scattering channels is large.

arXiv (Cornell University), Oct 4, 2003

Data indicate that ∆I = 3/2 transitions account for 4.5-4.7% of both CP conserving and CP violati... more Data indicate that ∆I = 3/2 transitions account for 4.5-4.7% of both CP conserving and CP violating K → 2π decays, as well as CP conserving radiative K → ππγ processes. Observed K → ππγ/ππ branching ratios are shown to scale near α/π or α/2π. The K L-K S mixing angle φ and the semileptonic weak-rate asymmetry δ are reviewed, and theory is shown to be consistent with data. Also, K → 2π ∆I = 1/2 dominance is studied in the context of the chiral constituent quark model, displaying again excellent agreement with data. Finally, indirect and direct kaon CP violation (CPV) are successfully described in the framework of photon-mediated quark-loop graphs. This suggests that kaon CPV can be understood via second-order weak transitions, radiatively corrected.

arXiv (Cornell University), Jun 3, 1998

It is shown that the incomplete scalar meson nonets found by Törnqvist [1] and Törnqvist & Roos [... more It is shown that the incomplete scalar meson nonets found by Törnqvist [1] and Törnqvist & Roos [2], employing a new version of the Helsinki unitarised quark model, should in fact be complete, including an as yet unconfirmed light K * 0 below 1 GeV (old κ) and the established f 0 (1500). A detailed comparison is presented with the predictions of the Nijmegen unitarised meson model, in which two complete scalar nonets show up below 1.5 GeV [3]. The reason for the flavour-nonet breaking found in Refs. [1, 2] we argue to originate in the use of coupling constants for the three-meson vertex which are not independent of flavour. Also some statements made in Ref. [1] are critically reviewed.

Acta Physica Polonica, 2018

Half a century of work on the light scalar mesons f 0 (500), f 0 (980), K ⋆ 0 (700), and a 0 (980... more Half a century of work on the light scalar mesons f 0 (500), f 0 (980), K ⋆ 0 (700), and a 0 (980) is briefly reviewed. After summarising all light scalar candidates in the Review of Particle Physics since 1963, a selection of different theoretical and phenomenological descriptions is presented, including pure meson-meson models, a tetraquark construction, unitarised quarkmeson models, unitarised effective chiral approaches, and a very recent lattice-QCD simulation.

Journal of Physics: Conference Series, 2019

New enhancements in the charmonium and bottomonium spectra observed since 2003 are very briefly r... more New enhancements in the charmonium and bottomonium spectra observed since 2003 are very briefly reviewed. Special attention is paid to χc1(3872) (formerly X(3872)) owing to its remarkable proximity to theD 0 D 0 threshold, which allows modelling as a quasibound axial-vector cc state with a largeD 0 D 0 admixture. In contrast, the interpretation of many other charmonium-like and bottomonium-like states is still very controversial and some may not even correspond to genuine resonances. Accordingly, several entries in the PDG tables have been wildly changing over the years. Three representative states are reviewed here as non-resonant enhancements due to threshold effects, viz. ψ(4260), ψ(4660), and Υ(10580).

Acta Physica Polonica B Proceedings Supplement, 2017

Mesons with masses below their lowest OZI-allowed strong-decay thresholds have very small widths.... more Mesons with masses below their lowest OZI-allowed strong-decay thresholds have very small widths. Thus, it is usually believed that they can be safely treated as pure quark-antiquark bound states in spectroscopy models. However, unitarised and coupled-channel models from decades ago already indicated that this may not be the case, owing to significant virtual meson-loop contributions. Recent unquenched lattice calculations that include two-meson interpolators besides the usual qq ones confirm the latter conclusion, in particular for the enigmatic narrow D s0 (2317), D s1 (2460), and X(3872) states. Here, we briefly review several predictions of some old and new quark models that go beyond the static description of mesons, also in comparison with up-to-date lattice results.

AIP Conference Proceedings, 2008

A panel discussion on scalar mesons was held with the participation of David Bugg, Yulia Kalashni... more A panel discussion on scalar mesons was held with the participation of David Bugg, Yulia Kalashnikova, Keh-Fei Liu, Michael Scadron, the author, and members of the audience. Some introductory remarks are noted here.

Physical Review D, 1983

A potential model for mesons is presented, which combines quark confinement and strong decay in a... more A potential model for mesons is presented, which combines quark confinement and strong decay in a realistic approach. The multichannel Schrodinger formalism is employed to describe a system of one or more permanently closed quark-antiquark channels in interaction with several two-meson channels. For the potential in the qq channels a harmonic oscillator with constant frequency is taken. As for the meson channels only Okubo-Zweig-Iizuka-rule-allowed decays into two mesons of the pseudoscalar or vector type are considered. Final-state interactions between these mesons are not yet taken into account. The communication between confined and free channels is supposed to take place via the 'I'0 mechanism, for which a locally approximated transition potential is derived. In order to obtain an analytic solution for the S matrix, the transition potential is treated by using a multi-5-shell method. Kinematically relativistic corrections and color splitting allow a fairly successful treatment of pseudoscalar as well as vector mesons for all quark flavors. The results are confronted with the data and discussed.

Physical Review D

In a recent paper by Gao et al. [Phys. Rev. D 105, 094002 (2022).], S-wave ππ scattering phase sh... more In a recent paper by Gao et al. [Phys. Rev. D 105, 094002 (2022).], S-wave ππ scattering phase shifts obtained in a lattice-QCD calculation are analyzed using dispersive S-matrix methods. We question the reliability of the conclusion from this analysis that, for a pion mass of 391 MeV, the lattice phases favor the presence of both a σ-meson bound state and a nearby virtual state. Our main criticism concerns the neglect of the S-wave KK channel, which was considered alongside additional ss interpolating fields in the lattice computation used by the authors of Gao et al. and also in typical coupled-channel models. As an illustration, some results from such a recent model are presented as well. Concluding remarks concern possible improvements of the analysis in Gao et al. as well as further model tests.