Evaluation of QCD sum rules for light vector mesons at finite density and temperature

QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of mass parameters for the lightest vector mesons ρ, ω and φ in a strongly interacting medium. For conditions relevant for the starting experiments at HADES we find that the in-medium mass shifts of the ρ- and ω-mesons are governed, within the Borel QCD sum rule approach, by the density and temperature dependence of the four-quark condensate. In particular, the variation of the strength of the density dependence of the four-quark condensate reflects directly the decreasing mass of the ρ-meson and can lead to a change of the sign of the ω-meson mass shift as a function of the density. In contrast, the in-medium mass of the φ-meson is directly related to the chiral strange quark condensate which seems correspondingly accessible. Received: 15 May 2002 / Accepted: 31 July 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: Kaempfer@fz.rossendorf.de Communicated by A. Sch?fer     

Confinement of tensor gluons — a classical approach

We look at the confinement of tensor gluons (f _μν ^(c) field) in a strong gravity background and find that the strong gravity provides a trap for the confinement of colour waves of selected frequencies. We assume that the tensorf _μν ^(c) field (mediating quanta: tensor 2⁺ f-meson) satisfies Einstein-like equations with a cosmological constant. The colour field satisfy equations resembling Maxwell form of the linear theory of gravitation and see the effect off _μν ^(c) field as playing the role of a medium having space dependent dielectric permeabilities. The solution of colour field equations resemble harmonic oscillator type wave functions with equispaced energy levels (no continuum) leading to confinement.     

BEPC共振事例的碎裂特性

发现e⁺e^－→J/ψ→3g三胶子碎裂的末态强子多重数〈n〉满足与e⁺e^－→q₀q₀连续区事例相同的普适质量关系〈n〉=A2S+12I+1exp(–bm2).表明胶子、夸克碎裂成强子时有相同的规律性.同样可以把参数A解释为直生介子、重子多重数〈M〉+〈B〉.虽然对Υ→3g与连续区事例进行比较,末态重子多重数增高2.5倍,但是利用我们对J/ψ→3g共振区的计算研究,没有发现J/ψ→3g事例有类似的特征.     

Mind the gap

In this summary of the application of Dyson-Schwinger equations to the theory and phenomenology of hadrons, some deductions following from a nonperturbative, symmetry-preserving truncation are highlighted, notable amongst which are results for pseudoscalar mesons. We also describe inferences from the gap equation relating to the radius of convergence of a chiral expansion, applications to heavy-light and heavy-heavy mesons, and quantitative estimates of the contribution of quark orbital angular momentum in pseudoscalar mesons; and recapitulate upon studies of nucleon electromagnetic form factors.     

Neutral color-spin-locking phase in neutron stars

We present results for the spin-1 color-spin-locking (CSL) phase using a NJL-type model in two-flavor quark matter for compact stars applications. The CSL condensate is flavor symmetric and therefore charge and color neutrality can easily be satisfied. We find small energy gaps ≃ 1MeV, which make the CSL matter composition and the EoS not very different from the normal quark matter phase. We keep finite quark masses in our calculations and obtain no gapless modes that could have strong consequences in the late cooling of neutron stars. Finally, we show that the region of the phase diagram relevant for neutron star cores, when asymmetric flavor pairing is suppressed, could be covered by the CSL phase.     

Two-prong πHe interactions at 106 MeV

π^-4He interactions at 106MeV, with two secondary charged particles in the final state, have been studied using a self-shunted streamer chamber in a 0.65T magnetic field and equipped with two CCD videocameras for obtaining digitized stereo-images of nuclear events occurring within the fiducial volume of the streamer chamber. Branching ratios for the various interaction channels are deduced. Evidence is presented for a reaction channel involving a γ produced in the final state, as well as for the first observation of direct Δ^- -resonance production. Cross-section distributions for the elastic and quasi-elastic interaction channels are also reported.     

Nucleon sigma term and quark condensate in nuclear matter

We study the bound-nucleon sigma term and the quark condensate in nuclear matter. In the quark-meson coupling (QMC) model the nuclear correction to the sigma term is small and negative, i.e., it decelerates the decrease of the quark condensate in nuclear matter. However, the quark condensate in nuclear matter is controlled primarily by the scalar-isoscalar σ field. Compared to the leading term, it moderates the decrease more than that of the nuclear sigma term alone at densities around and larger than the normal nuclear-matter density.