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M. F. M. Lutz

Publications and source records attributed to M. F. M. Lutz.

68 records · Page 4Linked to original sources
arXiv2003

On heavy-light meson resonances and chiral symmetry

We study heavy-light meson resonances with quantum numbers J^P=0^+ and J^P=1^+ in terms of the non-linear chiral SU(3) Lagrangian. At leading order a parameter-free prediction is obtained for the scattering of Goldstone bosons off heavy-light pseudo-scalar and vector mesons once we insist on approximate crossing symmetry of the unitarized scattering amplitude. The recently announced narrow open charm states observed by the BABAR and CLEO collaborations are reproduced. We suggest the existence of states that form an anti-triplet and a sextet representation of the SU(3) group. In particular, so far unobserved narrow isospin-singlet states with negative strangeness (I,S)=(0,-1) are predicted at 2361 MeV J^P=0^+ and 2501 MeV (J^P=1^+). Similarly, open bottom states are found at 5719 MeV (J^P=0^+) and 5622 MeV (J^P=1^+). Additional narrow states of mass 5580 MeV (J^P=0^+) and 5650 MeV (J^P=1^+) with widths of about 50 MeV are obtained in the (I,S)=(1,1) sector. For the anti-triplet states our results differ most significantly from predictions that are based on a linear realization of the chiral SU(3) symmetry in the open bottom sector. Strongly bound 0^+-and 1^+-states with (I,S)=(0,1) at 5507 MeV and 5553 MeV are predicted.

hep-ph↗
arXiv2003

Migdal's short range correlations in a covariant model

We construct a covariant model for short range correlations of a pion emerged in nuclear matter. Once the delta-hole contribution is considered an additional and so far neglected channel opens that leads to significant modifications in the vicinity of the kinematical region defined by ω\sim |\vec q |. We speculate that this novel effect should be important for the quantitative interpretation of charge exchange reactions like C(He,t).

nucl-th↗
arXiv2003

On baryon resonances and chiral symmetry

We study J^P=(3/2)^- baryon resonances as generated by chiral coupled-channel dynamics. Parameter free results are obtained in terms of the Weinberg-Tomozawa term predicting the leading s-wave interaction strength of Goldstone bosons with baryon-decuplet states. In the 'heavy' SU(3) limit with m_π= m_K \sim 500 MeV the resonances turn into bound states forming a decuplet and octet representation of the SU(3) group. Using physical masses the mass splitting are remarkably close to the empirical pattern.

nucl-th↗
arXiv2002

The relativistic nuclear dynamics for the SU(3) Goldstone bosons of chiral QCD

In this habilitation theses the chiral SU(3) Lagrangian is applied to antikaon and hyperon propagation in cold nuclear matter. The self consistent many-body dynamics relies on a detailed analysis of the pion, kaon and antikaon-nucleon scattering data with particular emphasis on constraints set by unitarity, covariance, causality and crossing symmetry. The work is based in large parts on collaborations with E.E. Kolomeitsev and C.L. Korpa and part of the results are published already. Unpublished results concern a discussion of the nature of baryon resonances in the context of coupled channel dynamics and a discussion of antikaon production in heavy-ion collisions at subthreshold energies. A new mechanism which drives the system towards equilibrium conditions is proposed. The theses contains also new results on the properties of antikaons and hyperon resonances in asymmetric nuclear matter.

nucl-th↗
arXiv2002

Scattering of vector mesons off nucleons

We construct a relativistic and unitary approach to 'high' energy pion- and photon-nucleon reactions taking the $πN, πΔ$, $ρN$, $ωN$, $ηN, K Λ, K Σ$ final states into account. Our scheme dynamically generates the s- and d-wave nucleon resonances N(1535), N(1650) and N(1520) and isobar resonances $Δ(1620)$ and $Δ(1700)$ in terms of quasi-local interaction vertices. The description of photon-induced processes is based on a generalized vector-meson dominance assumption which directly relates the electromagnetic quasi-local 4-point interaction vertices to the corresponding vertices involving the $ρ$ and $ω$ fields. We obtain a satisfactory description of the elastic and inelastic pion- and photon-nucleon scattering data in the channels considered. The resulting s-wave $ρ$- and $ω$-nucleon scattering amplitudes are presented. Using these amplitudes we compute the leading density modification of the $ρ$ and $ω$ energy distributions in nuclear matter. We find a repulsive energy shift for the $ω$ meson at small nuclear density but predict considerable strength in resonance-hole like $ω$-meson modes. Compared to previous calculations our result for the $ρ$-meson spectral function shows a significantly smaller in-medium effect. This reflects a fairly small coupling strength of the N(1520) resonance to the $ρN$ channel.

nucl-th↗
arXiv2002

From meson- and photon-nucleon scattering to vector mesons in nuclear matter

We present a relativistic and unitary approach to pion- and photon-nucleon scattering taking into account the $πN$, $ρN$, $ωN$, $ηN$, $πΔ$, $K Λ$ and $K Σ$ channels. Our scheme dynamically generates the s- and d-wave nucleon resonances N(1535), N(1650), N(1520) and N(1700) and isobar resonances $Δ(1620)$ and $Δ(1700)$ in terms of quasi-local two-body interaction terms. We obtain a fair description of the experimental data relevant for slow vector-meson propagation in nuclear matter. The s-wave $ρ$- and $ω$-meson nucleon scattering amplitudes, which define the leading density modification of the $ρ$- and $ω$-meson spectral functions in nuclear matter, are predicted.

nucl-th↗
arXiv2002

Quantum interference of rho0- and omega-mesons in the pi N -> e+e- N reaction

The study of the $πN\to ρ^0 N$ and $πN \to ωN$ amplitudes below and close to the vector meson production threshold ($1.4<\sqrt s <1.8$ GeV)reveals a rich structure arising from the presence of baryon resonances in this energy range. These resonances are reflected in the interference pattern of the $e^+e^-$ decays of the $ρ^0$- and $ω$-mesons produced in $π^- p$ and $π^+ n$ reactions. We discuss the shape and magnitude of the $ρ^0$-$ω$ interference in the $π^-p \to e^+e^- n$ and $π^+n \to e^+e^- p$ reaction cross sections as functions of the total center of mass energy $\sqrt s$. We find contrasted results: the interference is largely destructive for the $π^-p \to e^+e^- n$ cross section but constructive for the $π^+n \to e^+e^- p$ cross section. An experimental study of these reactions would provide significant constraints on the coupling of vector meson-nucleon channels to low-lying baryon resonances.

nucl-th↗
arXiv2001

Chiral SU(3) Symmetry and Strangeness

In this talk we review recent progress on the systematic evaluation of the kaon and antikaon spectral functions in dense nuclear matter based on a chiral SU(3) description of the low-energy pion-, kaon- and antikaon-nucleon scattering data.

nucl-th↗
arXiv2001

The $χ$-BS(3) approach

We present the results of the $χ$-BS(3) approach demonstrating that a combined chiral and 1/N_c expansion of the Bethe-Salpeter interaction kernel leads to a good description of the kaon-nucleon, antikaon-nucleon and pion-nucleon scattering data typically up to laboratory momenta of p_lab~500 MeV. We solve the covariant on-shell reduced coupled channel Bethe-Salpeter equation with the interaction kernel truncated to chiral order Q^3 and to the leading order in the 1/N_c expansion

nucl-th↗
arXiv2001

Self consistent propagation of hyperons and antikaons in nuclear matter based on relativistic chiral SU(3) dynamics

We evaluate the antikaon spectral density in isospin symmetric nuclear matter. The in-medium antikaon-nucleon scattering process and the antikaon propagation is treated in a self consistent and relativistic manner where a maximally scheme-independent formulation is derived by performing a partial density resummation in terms of the free-space antikaon-nucleon scattering amplitudes. The latter amplitudes are taken from a covariant and chiral coupled-channel SU(3) approach which includes s-, p- and d-waves systematically. Particular care is taken on the proper evaluation of the in-medium mixing of the partial waves. Our analysis establishes a rich structure of the antikaon spectral function with considerable strength at small energies. At nuclear saturation density we predict attractive mass shifts for the $Λ(1405)$, $Σ(1385)$ and $Λ(1520)$ of about 60 MeV, 60 MeV and 100 MeV respectively. The hyperon states are found to exhibit at the same time an increased decay width of about 120 MeV for the s-wave $Λ(1405)$, 70 MeV for the p-wave $Σ(1385)$ and 90 MeV for the d-wave $Λ(1520)$ resonance.

nucl-th↗
arXiv2001

Covariant meson-baryon scattering with chiral and large N_c constraints

We give a review of recent progress on the application of the relativistic chiral SU(3) Lagrangian to meson-baryon scattering. It is shown that a combined chiral and 1/N_c expansion of the Bethe-Salpeter interaction kernel leads to a good description of the kaon-nucleon, antikaon-nucleon and pion-nucleon scattering data typically up to laboratory momenta of p_lab about 500 MeV. We solve the covariant coupled channel Bethe-Salpeter equation with the interaction kernel truncated to chiral order Q^3 where we include only those terms which are leading in the large N_c limit of QCD.

nucl-th↗
arXiv2001

Relativistic chiral SU(3) symmetry, large N_c sum rules and meson-baryon scattering

The relativistic chiral SU(3) Lagrangian is used to describe kaon-nucleon scattering imposing constraints from the pion-nucleon sector and the axial-vector coupling constants of the baryon octet states. We solve the covariant coupled-channel Bethe-Salpeter equation with the interaction kernel truncated at chiral order Q^3 where we include only those terms which are leading in the large N_c limit of QCD. The baryon decuplet states are an important explicit ingredient in our scheme, because together with the baryon octet states they form the large N_c baryon ground states of QCD. Part of our technical developments is a minimal chiral subtraction scheme within dimensional regularization, which leads to a manifest realization of the covariant chiral counting rules. All SU(3) symmetry-breaking effects are well controlled by the combined chiral and large N_c expansion, but still found to play a crucial role in understanding the empirical data. We achieve an excellent description of the data set typically up to laboratory momenta of p_lab about 500 MeV.

nucl-th↗
arXiv1998

Dynamics of kaons in nuclear matter

We consider $K^-$ nucleon elastic and inelastic scattering in isospin symmetric nuclear matter. It is found that the proper description of the $Λ(1405)$ resonance structure in nuclear matter requires a self-consistent approach. Then the $Λ(1405) $ resonance mass remains basically unchanged, however, the resonance acquires an increased decay width as nuclear matter is compressed. The elastic and inelastic scattering amplitudes show important medium modifications close to the kaon nucleon threshold. We also construct the $K^-$-nuclear optical potential appropriate for $K^-$ atoms. Our microscopic approach predicts a strong attractive non-local interaction strength.

nucl-th↗