arXiv subjects

M. F. M. Lutz

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

At least 55 records · Page 3Linked to original sources

arXiv2006

Dynamically generated hidden-charm baryon resonances

Identifying a zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a rich spectrum of hadronic nuclei is formed. We argue that chiral symmetry and large-$N_c$ considerations determine that part of the interaction which generates the spectrum. We suggest the existence of strongly bound crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are narrow since they can decay only via OZI-violating processes.

hep-ph↗

arXiv2006

D-wave baryon resonances with charm from coupled-channel dynamics

Identifying the zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, the spectrum of ${3/2}^-$ molecules is computed. We predict a strongly bound 15-plet of $C=-1$ states. A narrow crypto-exotic octet of charm-zero states is foreseen. In the $C=+1$ sector a sextet of narrow resonances is formed due to the interaction of D mesons with the baryon decuplet. A strongly bound triplet of double-charm states is a consequence of coupled-channel dynamics driven by the D mesons.

hep-ph↗

arXiv2006

Baryon self energies in the chiral loop expansion

We compute the self energies of the baryon octet and decuplet states at the one-loop level applying the manifestly covariant chiral Lagrangian. It is demonstrated that expressions consistent with the expectation of power counting rules arise if the self energies are decomposed according to the Passarino-Veltman scheme supplemented by a minimal subtraction. This defines a partial summation of the chiral expansion. A finite renormalization required to install chiral power counting rules leads to the presence of an infrared renormalization scale. Good convergence properties for the chiral loop expansion of the baryon octet and decuplet masses are obtained for natural values of the infrared scale. A prediction for the strange-quark matrix element of the nucleon is made.

nucl-th↗

arXiv2005

Dynamically generated baryon resonances

Identifying a zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a rich spectrum of molecules is formed. We argue that chiral symmetry and large-$N_c$ considerations determine that part of the interaction which generates the spectrum. We suggest the existence of strongly bound crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are narrow since they can decay only via OZI-violating processes. A narrow nucleon resonance is found at mass 3.52 GeV. It is a coupled-channel bound state of the $(η_c N), (\bar D Σ_c)$ system, which decays dominantly into the $(η' N)$ channel. Furthermore two isospin singlet hyperon states at mass 3.23 GeV and 3.58 GeV are observed as a consequence of coupled-channel interactions of the $(\bar D_s Λ_c), (\bar D Ξ_c)$ and $(η_c Λ),(\bar D Ξ_c')$ states. Most striking is the small width of about 1 MeV of the lower state. The upper state may be significantly broader due to a strong coupling to the $(η' Λ)$ state. The spectrum of crypto-exotic charm-zero states is completed with an isospin triplet state at 3.93 GeV and an isospin doublet state at 3.80 GeV. The dominant decay modes involve again the $η'$ meson.

hep-ph↗

arXiv2005

Open-charm systems in cold nuclear matter

We study the spectral distributions of charmed meson with $J^P=0^-$ quantum numbers in cold nuclear matter applying a self-consistent and covariant many-body approach established previously for the nuclear dynamics of kaons. At leading orders the computation requires as input the free-space two-body scattering amplitudes only. Our results are based on the s-wave meson-nucleon amplitudes obtained recently in terms of a coupled-channel approach. The amplitudes are characterized by the presence of many resonances in part so far not observed. This gives rise to an intriguing dynamics of charmed mesons in nuclear matter. At nuclear saturation density we predict a pronounced two-mode structure of the $D^+$ mesons with a main branch pushed up by about 32 MeV. The lower branch reflects the coupling to two resonance-hole states that are almost degenerate. For the $D^-$ we obtain a single mode pushed up by about 18 MeV relative to the vacuum mode. Most spectacular are the results for the $D^+_s$ meson. The presence of an exotic resonance-hole state gives rise to a rather broad and strongly momentum dependent spectral distribution.

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arXiv2005

Coupled-channel study of crypto-exotic baryons with charm

Identifying the t-channel exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a surprisingly rich spectrum of molecules is formed. We argue that chiral symmetry and large- N_c considerations determine that part of the interaction which generates the spectrum. All channels that are required by the existence of (u,d,s,c) quarks are considered. A bound state with exotic quantum numbers is predicted at mass 2.78 GeV. It couples strongly to the (bar D_s N),(bar D Lambda),(bar D Sigma) channels. A further charm minus-one system is predicted at mass 2.84 GeV as a result of (bar D_s Lambda), (bar D Xi) interactions. We suggest the existence of strongly bound crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are narrow since they can decay only via OZI-violating processes. A narrow nucleon resonance is found at mass 3.52 GeV. It is a coupled-channel bound state of the (eta_c N), (bar D Sigma_c) system, which decays dominantly into the (eta' N) channel. Furthermore two isospin singlet hyperon states at mass 3.23 GeV and 3.58 GeV are observed as a consequence of coupled-channel interactions of the (bar D_s Lambda_c), (bar D Xi_c) and (eta_c Lambda),(bar D Xi_c') states. Most striking is the small width of about 1 MeV of the lower state. The upper state may be significantly broader due to a strong coupling to the (eta' Lambda) state. The two so far observed s-wave baryons with charm one are recovered. We argue that the Lambda_c(2880) is not a s-wave state. In addition to those states we predict the existence of about ten narrow s-wave baryon states with masses below 3 GeV.

hep-ph↗

arXiv2005

Kaon and antikaon properties in cold nuclear medium

We present results of a self-consistent calculation for the kaon and antikaon spectral functions in cold nuclear matter, using as input the kaon-nucleon and antikaon-nucleon scattering amplitudes of the vacuum. We investigate the effect of in-medium pion dressing on the antikaon-nucleon scattering amplitudes and antikaon spectral function. We find the influence of pion dressing to be minor on the antikaon spectral function and limited on the hyperon resonances causing only a small additional broadening. An exception is the Σ(1690). At nuclear saturation density an attractive mass shift of about 20 MeV and width of about 130 MeV is obtained. The kaon shows a repulsive mass increase of 36 MeV and a small width of the quasiparticle peak at saturation density.

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arXiv2005

Baryon resonances from chiral coupled-channel dynamics

We discuss the formation of s- and d-wave baryon resonances as predicted by the chiral SU(3) symmetry of QCD. Based on the leading order term of the chiral Lagrangian a rich spectrum of molecules is generated, owing to final-state interactions. The spectrum of s- and d-wave baryon states with zero and non-zero charm is remarkably consistent with the empirical pattern. In particular, the recently announced Sigma_c(2800) of the BELLE collaboration is reproduced with realistic mass and width parameters. Similarly, the d-wave states Lambda_c(2625) and Xi_c(2815) are explained naturally to be chiral excitations of J^P=3/2^+ states. In the open-charm sector exotic multiplet structures are predicted. These findings support a radical conjecture: meson and baryon resonances that do not belong to the large-N_c ground state of QCD should be viewed as hadronic molecular states

hep-ph↗

arXiv2004

Chiral dynamics for exotic open-charm resonances

We review the open-charm spectrum of chiral excitations in QCD. At leading order in a chiral expansion a parameter-free prediction is obtained for the coupled-channel scattering of Goldstone bosons off open-charm mesons and baryons with 0^-,1^- and {1/2}^+ quantum numbers. The recently announced narrow D_s(2317) and $D_s(2463)$ mesons observed by the BABAR and CLEO collaborations are reproduced. Also the baryon states Λ_{c}(2593), Λ_{c}(2880) and Ξ_{c}(2790) discovered earlier by the CLEO collaboration are recovered naturally. Besides describing resonances with conventional quantum numbers additional multiplets with members that carry exotic quantum numbers are predicted. In particular, so far unobserved narrow isospin-singlet open-charm mesons with negative strangeness are generated dynamically. Similarly, narrow isospin-doublet open-charm baryons with positive strangeness are suggested.

hep-ph↗

arXiv2004

Self consistent and covariant propagation of pions, nucleon and isobar resonances in cold nuclear matter

We evaluate the in-medium spectral functions for pions, nucleon and isobar resonances in a self consistent and covariant manner. The calculations are based on a recently developed formulation which leads to predictions in terms of the pion-nucleon scattering phase shifts and a set of Migdal parameters describing important short range correlation effects. We do not observe significant softening of pion modes if we insist on reasonable isobar resonance properties but predict a considerable broadening of the N(1440) and N(1520) resonances in nuclear matter. Contrasted results are obtained for the s-wave N(1535) and N(1650) resonances which are affected by a nuclear environment very little. The properties of slowly moving isobar's in nuclear matter are found to depend very sensitively on a soft form factor in the piNN vertex, which is not controlled by the piN scattering data.

nucl-th↗

arXiv2004

Chiral symmetry, strangeness and resonances

We review the important role played by the chiral SU(3) symmetry in predicting the properties of antikaons and hyperon resonances in cold nuclear matter. Objects of crucial importance are the meson-baryon scattering amplitudes obtained within the chiral coupled-channel effective field theory. The formation of baryon resonances as implied by chiral coupled-channel dynamics is discussed. Results for antikaon and hyperon-resonance spectral functions are presented for isospin symmetric and asymmetric matter.

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arXiv2004

Chiral symmetry and resonances in QCD

We study the formation of resonances in terms of the chiral SU(3) Lagrangian. At leading order parameter-free predictions are obtained for the scattering of Goldstone bosons off any hadron once we insist on approximate crossing symmetry of the unitarized scattering amplitude. A wealth of empirically established resonances are recovered and so far unseen resonances are predicted. Here we review in some detail the properties of light axial-vector mesons.

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arXiv2004

Quark-mass dependence of baryon resonances

We study the quark-mass dependence of J^P = \frac12^- s-wave and J^P = \frac32^- d-wave baryon resonances. Parameter-free results are obtained in terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with m_π=m_K \simeq 500 MeV the s-wave resonances turn into bound states forming two octets plus a singlet representations of the SU(3) group. Similarly the d-wave resonances turn into bound states forming an octet and a decuplet in this limit. A contrasted result is obtained in the 'light' SU(3) limit with m_π=m_K \simeq 140 MeV for which no resonances exist.

nucl-th↗

arXiv2003

Quark mass dependence of s-wave baryon resonances

We study the quark mass dependence of $J^P = \frac12^-$ s-wave baryon resonances. Parameter free results are obtained in terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with $m_π=m_K \simeq $ 500 MeV the resonances turn into bound states forming two octets plus a singlet representations of the SU(3) group. A contrasted result is obtained in the 'light' SU(3) limit with $m_π=m_K \simeq $ 140 MeV for which no resonances exist. Using physical quark masses our analysis suggests to assign to the $S=-2$ resonances $Ξ(1690)$ and $Ξ(1620)$ the quantum numbers $J^P=1/2^-$.

nucl-th↗

arXiv2003

On meson resonances and chiral symmetry

We study meson resonances with quantum numbers J^P=1^+ in terms of the chiral SU(3) Lagrangian. At leading order a parameter-free prediction is obtained for the scattering of Goldstone bosons off vector mesons with J^P=1^- once we insist on approximate crossing symmetry of the unitarized scattering amplitude. A resonance spectrum arises that is remarkably close to the empirical pattern. In particular, we find that the strangeness-zero resonances h_1(1380), f_(1285) and b_1(1235) are formed due to strong K \bar K_μand \bar K K_μchannels. This leads to large coupling constants of those resonances to the latter states.

nucl-th↗

arXiv2003

Charmed meson resonances from chiral coupled-channel dynamics

Charmed meson resonances with quantum numbers J^P=0^+ and J^P=1^+ are generated in terms of chiral coupled-channel dynamics. At leading order in the chiral expansion a parameter-free prediction is obtained for the scattering of Goldstone bosons off charmed pseudo-scalar and vector mesons. 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 are predicted.

hep-ph↗

arXiv2003

On charm baryon resonances and chiral symmetry

We study heavy-light baryon resonances with quantum numbers J^P=1/2^- in terms of the non-linear chiral SU(3) Lagrangian. Within the chi-BS(3) approach a parameter-free leading order prediction is obtained for the scattering of Goldstone bosons off heavy-light baryon resonances with J^P=1/2^+. The three states Lambda_{c1}(2593), Lambda_{c0}(2880) and Xi_{c1}(2790) discovered by the CLEO collaboration are recovered. We suggest the existence of resonance states that form an anti-quindecimplet, two sextet and two anti-triplet representations of the SU(3) group. In particular, narrow states with anomalous isospin (I) and strangeness (S) quantum numbers (I,S)=(1/2,+1) are anticipated.

hep-ph↗

arXiv2003

Open-charm meson resonances with negative strangeness

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. Adjusting the free parameters that arise at subleading order to reproduce the mass of the D(2420) resonance as well as the new states established recently by the BABAR, CLEO and BELLE collaborations we obtain refined masses for the anti-triplet and sextet states. Bound states of antikaons at the D(1867) and D(2008) mesons are predicted at 2352 MeV (J^P=0^+) and 2416 MeV (J^P=1^+). In addition we anticipate a narrow scalar state of mass 2389 MeV with (I,S)=(1/2,0)

hep-ph↗