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Ulf-G. Meißner

Publications and source records attributed to Ulf-G. Meißner.

At least 487 records · Page 27Linked to original sources
arXiv2006

More on the infrared renormalization group limit cycle in QCD

We present a detailed study of the recently conjectured infrared renormalization group limit cycle in QCD using chiral effective field theory. It was conjectured that small increases in the up and down quark masses can move QCD to the critical trajectory for an infrared limit cycle in the three-nucleon system. At the critical quark masses, the binding energies of the deuteron and its spin-singlet partner are tuned to zero and the triton has infinitely many excited states with an accumulation point at the three-nucleon threshold. We exemplify three parameter sets where this effect occurs at next-to-leading order in the chiral counting. For one of them, we study the structure of the three-nucleon system in detail using both chiral and contact effective field theories. Furthermore, we investigate the matching of the chiral and contact theories in the critical region and calculate the influence of the limit cycle on three-nucleon scattering observables.

hep-ph↗
arXiv2006

On the strong energy dependence of the e^+e^- to ppbar amplitude near threshold

We study the energy dependence of the e^+e^- to ppbar cross section close to the two-nucleon threshold, recently reported by the BaBar collaboration. Our analysis also includes the pbarp to e^+e^- data collected by PS170 collaboration and the e^+e^- to NNbar data from the FENICE collaboration. We show that the near-threshold enhancement in the e^+e^- to ppbar cross section can be explained by the final-state interaction between proton and antiproton in the 3S1 partial wave, utilizing the Juelich nucleon-antinucleon model. As a consequence, the strong dependence of the proton electromagnetic form factors on the momentum transfer close to the two-nucleon threshold is presumably also driven by this final-state interaction effect. This result is in line with our previous studies of the near-threshold enhancement of the ppbar invariant mass spectrum seen in the J/Psi to gamma ppbar decay by the BES collaboration and in the B+ to ppbar K+ decay by the BaBar collaboration.

hep-ph↗
arXiv2006

The nucleon axial-vector coupling beyond one loop

We analyze the nucleon axial-vector coupling to two loops in chiral perturbation theory. We show that chiral extrapolations based on this representation require lattice data with pion masses below 300 MeV.

hep-lat↗
arXiv2006

ppbar enhancement in B and J/Psi decay

The near-threshold enhancement in the ppbar invariant mass spectrum from the B^+ -> K^+ ppbar decay reported recently by the BaBar Collaboration is studied within the Jülich NNbar model. We illustrate that the invariant mass dependence of the ppbar spectrum close to the threshold can be reproduced by the final state interactions. This explanation is in line with our previous analysis of the ppbar invariant mass spectrum from the J/Psi -> gamma ppbar decay measured by the BES Collaboration. We also comment on a structure found recently in the pi^+ pi^- eta' mass spectrum of the radiative J/Psi decay by the BES Collaboration. In particular we argue that one should be rather cautions in bringing this structure in connection with the enhancement found in the ppbar invariant mass spectrum or with the existence of NNbar bound states.

hep-ph↗
arXiv2006

The reaction pi N to pi pi N in a meson-exchange approach

A resonance model for two-pion production in the pion-nucleon reaction is developed that includes information obtained in the analysis of pion-nucleon scattering in a meson-exchange model. The baryonic resonances Delta(1232), N*(1440), N*(1520), N*(1535), and N*(1650) are included. The model reproduces the total cross sections up to kinetic energies of the incident pion of 350 MeV and obtains the shapes of the differential cross sections in reasonable agreement with the data.

nucl-th↗
arXiv2006

Kaon-nucleon scattering lengths from kaonic deuterium experiments

The extraction of the S-wave kaon-nucleon scattering lengths a0 and a1 from a combined analysis of existing kaonic hydrogen and synthetic deuterium data has been carried out within the framework of a low-energy effective field theory. It turns out that with the present DEAR central values for the kaonic hydrogen ground-state energy and width, a solution for a0 and a1 exists only in a restricted domain of input values for the kaon-deuteron scattering length. Consequently, measuring this scattering length imposes stringent constraints on the theoretical description of the kaon-deuteron interactions at low energies.

nucl-th↗
arXiv2006

Omega-phi mixing in chiral perturbation theory

We investigate omega-phi meson mixing to leading order in chiral perturbation theory utilizing the antisymmetric tensor field formulation. We update the quark mass ratio R from rho-omega mixing, R = 42 \pm 4.

hep-ph↗
arXiv2006

Testing the nature of the $Λ(1520)$ resonance in proton-induced production

The $Λ(1520)$ resonance has been recently studied in a unitarized coupled channel formalism with $πΣ(1385)$, $KΞ(1530)$, $\bar{K}N$ and $πΣ$ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of the $pp\to pK^+K^-p$ and $pp\to pK^+π^0π^0Λ$ reactions. In particular, we show that the ratio between the $π^0π^0Λ$ and $K^-p$ mass distributions can provide valuable information on the ratio of the couplings of the $Λ(1520)$ resonance to $πΣ(1385)$ and $\bar{K}N$ that the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at Jülich or the developing CSR facility at Lanzhou.

nucl-th↗
arXiv2005

Novel evaluation of the two-pion contribution to the nucleon isovector form factors

We calculate the two-pion continuum contribution to the nucleon isovector spectral functions drawing upon the new high statistics measurements of the pion form factor by the CMD-2, KLOE, and SND collaborations. The general structure of the spectral functions remains unchanged, but the magnitude increases by about 10%. Using the updated spectral functions, we calculate the contribution of the two-pion continuum to the nucleon isovector form factors and radii. We compare the isovector radii with simple rho-pole models and illustrate their strong underestimation in such approaches. Moreover, we give a convenient parametrization of the result for use in future form factor analyses.

hep-ph↗
arXiv2005

Isospin-breaking corrections in the pion-deuteron scattering length

It is shown that isospin-breaking corrections to the pion-deuteron scattering length can be very large, because of the vanishing of the isospin-symmetric contribution to this scattering length at leading order in chiral perturbation theory. We further demonstrate that these corrections can explain the bulk of the discrepancy between the recent experimental data on pionic hydrogen and pionic deuterium. We also give the first determination of the electromagnetic low-energy constant f1.

nucl-th↗
arXiv2005

The pion-nucleon scattering lengths from pionic deuterium

We use the framework of effective field theories to discuss the determination of the S-wave πN scattering lengths from the recent high-precision measurements of pionic deuterium observables. The theoretical analysis proceeds in several steps. Initially, the precise value of the pion-deuteron scattering length a_{πd} is extracted from the data. Next, a_{πd} is related to the S-wave πN scattering lengths a_+ and a_-. We discuss the use of this information for constraining the values of these scattering lengths in the full analysis, which also includes the input from the pionic hydrogen energy shift and width measurements, and throughly investigate the accuracy limits for this procedure. In this paper, we also give a detailed comparison to other effective field theory approaches, as well as with the earlier work on the subject, carried out within the potential model and multiple scattering framework.

nucl-th↗
arXiv2005

B_{s,d}\to γγdecay in the model with one universal extra dimension

We estimate the beyond the Standard Model (SM) contribution to the B_{s,d} \to γγdouble radiative decay in the framework of the model with one universal extra dimension. This contribution gives a \sim 3 (6)% enhancement of the branching ratio calculated in the SM for B_{s (d)} \to γγ.

hep-ph↗
arXiv2005

The Juelich hyperon-nucleon model revisited

A one-boson-exchange model for the hyperon-nucleon (ΛN, ΣN) interaction is presented. The model incorporates the standard one boson exchanges of the lowest pseudoscalar and vector meson multiplets with coupling constants fixed by SU(6) flavor symmetry relations. As the main new feature of the model, the contributions in the scalar--isoscalar (σ) and vector--isovector (ρ) exchange channels are now constrained by a microscopic model of correlated ππand K \bar K exchange. Additional short-ranged ingredients of the model in the scalar--isovector (a_0) and scalar--isospin-1/2 (κ) channels are likewise viewed as arising from meson-meson correlations but are treated phenomenologically. With this model a satisfactory reproduction of the available hyperon-nucleon data can be achieved.

nucl-th↗
arXiv2005

Quark mass dependence of baryon properties

I discuss the quark mass dependence of various baryon properties derived from chiral perturbation theory. Such representations can eventually be used as chiral extrapolation functions when lattice data at sufficiently small quark masses become available. The quark mass dependence is encoded in loop and contact term contributions, the latter given in terms of low-energy constants. I stress the importance of utilizing phenomenological input to constrain a certain class of low-energy constants and discuss the ensuing theoretical uncertainty for various baryon observables, like the nucleon and the baryon octet masses, the nucleon isovector anomalous magnetic moment and the axial-vector coupling of the nucleon. I stress the role of resonance decoupling and present first results for the delta mass based on an effective field theory in which the nucleon-delta mass splitting is counted as a small parameter. I also discuss briefly the pion mass dependence of the nuclear force as derived from chiral nuclear effective field theory.

hep-lat↗
arXiv2005

Chiral Extrapolations and the Covariant Small Scale Expansion

We calculate the nucleon and the delta mass to fourth order in a covariant formulation of the small scale expansion. We analyze lattice data from the MILC collaboration and demonstrate that the available lattice data combined with our knowledge of the physical values for the nucleon and delta masses lead to consistent chiral extrapolation functions for both observables up to fairly large pion masses. This holds in particular for very recent data on the delta mass from the QCDSF collaboration. The resulting pion-nucleon sigma term is sigma_{piN} = 48.9 MeV. This first quantitative analysis of the quark-mass dependence of the structure of the Delta(1232) in full QCD within chiral effective field theory suggests that (the real part of) the nucleon-delta mass-splitting in the chiral limit, Delta_0 = 0.33 GeV, is slightly larger than at the physical point. Further analysis of simultaneous fits to nucleon and delta lattice data are needed for a precision determination of the properties of the first excited state of the nucleon.

hep-lat↗
arXiv2005

The Fubini-Furlan-Rosetti sum rule and related aspects in light of covariant baryon chiral perturbation theory

We analyze the Fubini-Furlan-Rosetti sum rule in the framework of covariant baryon chiral perturbation theory to leading one-loop accuracy and including next-to-leading order polynomial contributions. We discuss the relation between the subtraction constants in the invariant amplitudes and certain low-energy constants employed in earlier chiral perturbation theory studies of threshold neutral pion photoproduction off nucleons. In particular, we consider the corrections to the sum rule due to the finite pion mass and show that below the threshold they agree well with determinations based on fixed-t dispersion relations. We also discuss the energy dependence of the electric dipole amplitude E_{0+}.

nucl-th↗
arXiv2005

Okubo-Zweig-Iizuka rule violation in photoproduction

We investigate OZI rule violation in omega and phi-meson photoproduction off nucleons. Data on the total cross sections indicate a large phi/omega ratio of about 0.8 at the maximal available photon energy that is in good agreement with expectations from QCD. On the other hand, data at large four momentum transfer exhibit a ratio of about 0.07, showing that the perturbative QCD regime is not approached at |t| > 2 GeV^2 and photon energies E_γ< 4 GeV. The anomanously large phi/omega ratio at low energies, that is close to the reaction threshold, remains to be explained within nonperturbative QCD.

hep-ph↗