Role of the effective nucleon mass for pion condensation in nuclear matter

The dependence of the threshold for pion condensation in symmetric nuclear matter on the effective nucleon mass $\text{M}{}^1$ is investigated, using extrapolations of $\text{M}{}^1\text{(?)}$ to high densities ?, based on boson exchange mechanisms. It is found that if $\text{M}{}^1\text{(?)}$ decreases below the standard value $\text{M}{}^1\text{=0.8M}$ as the density increases beyond the nuclear matter density ?₀, the critical density is raised considerably beyond ?₀ once short-range repulsive correlations are included.     

The origin of the pion mass

We discuss the origin of the pion mass using a simple model of the QCD vacuum as a condensate of overlapping quark-antiquark pairs. We analyze the relationship between local conservation of the axial current and the nonzero current quark mass. Away from the chiral limit, we find that the pion mass comes from a change in the geometry of the overlap of condensed pairs.     

The pion mass difference in threshold pion reactions on light nuclei

We investigate the effect of the pion mass difference in scattering and photoproduction of pions on light nuclei near threshold. The effect is found to be most easily described in a nuclear K-matrix formalism where the nuclear K-matrix elements are shown to be independent of the mass difference.     

The pion mass in finite volume

We determine the relative pion mass shift due to the finite spatial extent L of the box by means of two-flavor chiral perturbation theory and the one-particle Lüscher formula. We use as input the expression for the infinite volume forward scattering amplitude up to next-to-next-to-leading order and can therefore control the convergence of the chiral series. A comparison to the full leading order chiral expression for the pion mass in finite volume allows us to check the size of subleading terms in the large-L expansion.Received: 19 November 2003, Published online: 18 February 2004     

Neutral pion decays probe new physics beyond the standard model

We study the decay π⁰ → γ + unobservable particles. The observation of such a process would give unambiguous evidence for the existence of a new light gauge boson of the type predicted by a number of current models. It is shown that the decay rate of the production of such a boson can be experimentally interesting. The contribution of the background processes (π⁰ → γ + scalars, π⁰ → γ + fermions) is proved to be negligibly small.     

Glueballs at physical pion mass

Glueballs are investigated through gluonic operators on two N_f= 2 + 1RBC/UKQCD gauge ensembles at the physical pion mass. The statistical errors of glueball correlation functions are considerably reduced through the cluster decomposition error reduction(CDER) method. The Bethe-Salpeter wave functions are obtained for the scalar, tensor, and pseudoscalar glueballs by using spatially extended glueball operators defined through the gauge potential A_μ(x)in the Coulomb gauge. Th...     

Magnitude of Regge cut contributions in the triple-Regge region

Starting from the reggeon calculus, the various possibilities of absorptive pomeron cut corrections in the triple-Regge region are considered. For the case of pp → pX, we estimate their importance at present day energies. We conclude that at highest ISR energies, pomeron cuts of the eikonal type are not enough, and enhanced diagrams with at least one additional triple-pomeron coupling need be included.     

Quark mass dependence of the pion vector form factor

We examine the quark mass dependence of the pion vector form factor, particularly the curvature (mean quartic radius). We focus our study on the consequences of assuming that the coupling constant of the ρ   to pions, g_ρππ$g_{\rho \pi \pi }$, is largely independent of the quark mass while the quark mass dependence of the ρ mass is given by recent lattice data. By employing the Omnès representation we can provide a very clean estimate for a certain combination of the curvature and the square radius, whose quark mass dependence could be determined from lattice computations. This study provides an independent access to the quark mass dependence of the ρππ   coupling and in this way a non-trivial check of the systematics of chiral extrapolations. We also provide an improved value for the curvature for physical values for the quark masses, namely 〈r⁴〉=0.73±0.09 fm⁴$〈r^4〉=0.73\pm 0.09{\text{fm}}^4$ or equivalently cV=4.00±0.50 GeV−4$c_V=4.00\pm 0.50{\text{GeV}}^{-4}$.     

Meson screening mass in a strongly coupled pion superfluid

We calculate the meson screening mass in a pion superfluid in the framework of Nambu–Jona-Lasinio model. The minimum of the attractive quark potential is always located at the phase boundary of pion superfluid. Different from the temperature and baryon density effect, the potential at finite isospin density cannot be efficiently suppressed and the matter is always in a strongly coupled phase due to the Goldstone mode in the pion superfluid.     

大学物理教学中的相对论质量浅议

分析了大学物理教材中相对论质量公式推导部分容易引起学生误解的核心:质量守恒关系式.通过引入二维运动给出了更合理的推导过程.     

Role of temperature in the physics of metallic clusters

The finite temperature of the ionic degrees of freedom plays either a determining or an important role in a large variety of cluster properties. We briefly review here the role played by the temperature in different cluster phenomena, such as: occurrence of phase transitions, shape fluctuations, detailed properties of the static and dynamic structure formfactors, of the electron single-particle spectra and of the optical response, and the emergence of the 1/f-noise in ionic dynamics. Presented at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Role ofΔ(1232) in pion condensation in16O

We investigate the effect of Δ(1232) in pion condensation in¹⁶O within a model where the spins of all protons are oriented in one direction and those of neutrons in opposite direction. Both the π and the ρ exchange interactions have been considered. The effect of the Δ(1232) is found to be important.