Narrow Results

In this paper, it is shown how a chiral Lagrangian framework can be used to derive relationships connecting quark-level QCD correlation functions to mesonic-level two-point functions. Crucial ingredients of this connection are scale factor matrices relating each distinct quark-level substructure (e.g. quark–antiquark, four-quark) to its mesonic counterpart. The scale factors and mixing angles are combined into a projection matrix to obtain the physical (hadronic) projection of the QCD correlation function matrix. Such relationships provide a powerful bridge between chiral Lagrangians and QCD sum-rules that are particularly effective in studies of the substructure of light scalar mesons with multiple complicated resonance shapes and substantial underlying mixings. The validity of these connections is demonstrated for the example of the isotriplet $a_0(980)\text{–}{a}_0(1450)$ system, resulting in an unambiguous determination of the scale factors from the combined inputs of QCD sum-rules and chiral Lagrangians. These scale factors lead to a remarkable agreement between the quark condensates in QCD and the mesonic vacuum expectation values that induce spontaneous chiral symmetry breaking in chiral Lagrangians. This concrete example shows a clear sensitivity to the underlying $a_0$-system mixing angle, illustrating the value of this methodology in extensions to more complicated mesonic systems.

The DEAR (DAΦNE Exotic Atom Research) experiment¹ measured the energy of X-rays emitted in the transitions to the ground states of kaonic hydrogen. The shift ∊ and the width Γ of the 1s state are sensitive quantities for tests of the current understanding of the low energy antikaon-nucleon interaction. We obtain ∊_1s=-193±37 (stat.)±6 (syst.) and Γ_1s=249±112 (stat.)±30 (syst.).

Within a linear sigma model framework, possible mixing between two chiral nonets (a two quark nonet, and a four quark nonet) below 2 GeV is studied. Incorporating the U(1)_A behavior of the underlying QCD, and working in the isospin invariant limit, the mass spectra of the I = 0, I = 1/2 and I = 1 pseudoscalars, and the I = 1/2 scalars are studied, and estimates of their quark content are presented. It is found, as expected, that the ordinary and the excited pseudoscalars generally have much less two and four quark admixtures compared to the respective scalars. As by-products, several quantities such as the four quark vacuum condensate, and the decay constant of excited states are predicted.

The AMADEUS experiment will give a first conclusive answer to the question on the existence of the deeply bound kaonic states, which is discussed quite controversially in the hadron physics community today. Using the KLOE detector system together with the AMADEUS apparatus an exclusive measurement will be performed that means a complete determination of all formation and decay channels of kaonic nuclear states is possible in the reaction using ³He and ⁴He targets. The upgraded high luminosity DAɸNE e⁺e^- collider at LNF is essential for successful measurements. Using missing mass and invariant mass spectroscopy a conclusive observation of these exotic objects should be reachable, and their properties, such as binding energies, total and partial widths, size and density could be determined. Thus, will open a new field in the spectroscopy of di- and tri-baryon systems with strangeness (S = -1).

With the primary motivation of probing the quark substructure of scalar mesons, a generalized linear sigma model for the lowest and the next-to-lowest scalar and pseudoscalar mesons is employed to investigate several semileptonic decays of D mesons. The free parameters of the model (in its leading approximation) have been previously determined from fits to mass spectra and various low-energy parameters. With these fixed parameters, the model has already given encouraging predictions for different low-energy decays and scattering, as well as for semileptonic decay channels of that include a scalar meson in the final state. In the present work, we apply the same model (in its leading order with the same fixed parameters) to different semileptonic decay channels of , D⁺ and D⁰. Although these decay channels produce only pseudoscalar mesons in the final states, since various properties of scalar mesons have been used in fixing the model parameters, this study further tests the model and its predictions for the quark substructure of both pseudoscalar as well as scalar mesons. We find that these predictions are in qualitative agreement with experiment.

Gerry Brown has played a major role in initiating and stimulating systematic work on the theories of nuclear forces. It is the purpose of this paper to review those theories — in his memory.

Global symmetries and symmetry breaking patterns of QCD with light quarks, in particular chiral symmetry, provide basic guidance not only for low-energy hadron physics but also for nuclear forces and the nuclear many-body problem. Recent developments of Chiral Effective Field Theory (ChEFT) applications to nuclear and neutron matter are summarized, with special emphasis on a (nonperturbative) extension using functional renormalization group methods. Topics include: nuclear thermodynamics, extrapolations to dense baryonic matter and constraints from neutron star observables.

Gerry Brown has played a major role in initiating and stimulating systematic work on the theories of nuclear forces. It is the purpose of this paper to review those theories — in his memory.