In a previous paper, we have shown that a double phi peak structure appears in the dilepton invariant mass spectrum if a first order QCD phase transition occurs in ultrarelativistic heavy-ion collisions. Furthermore, the transition temperature can be determined from the transverse momentum distribution of the low mass phi peak. In this work, we extend the study to the case that a smooth crossover occurs in the quark-gluon plasma to the hadronic matter transition. We find that the double phi peak structure still exists in the dilepton spectrum and thus remains a viable signal for the formation of the quark-gluon plasma in ultrarelativistic heavy-ion collisions.

The transport theory for a quark-antiquark plasma is used to study large time-scale fluctuations of the quark condensate. The interactions between quarks are assumed to be of the Nambu–Jona-Lasino type and we restrict ourselves to the mean field (Vlasov) approximation. The space-time behavior of the fluctuations of the mean field and, consequently, of the condensate depends strongly on the form of the initial conditions for the quark distribution function. If the latter can be initially represented as a sum of the thermal background distribution plus a perturbation which is broad in momentum, then the fluctuations are suppressed in time by a mechanism analogous to that of Landau damping. On the other hand, if we add a perturbation which is peaked in momentum to the thermal background distribution, the fluctuations are not damped and behave similarly to Van Dampen modes in ordinary plasmas.

An extended pion source, which can be temporarily created by a high energy nuclear collision, will also absorb and distort the outgoing pions. We discuss how this effect alters the interferometric pattern of the two-pion momentum correlation function. In particular, we show that the two-pion correlation function decreases rapidly when the opening angle between the pions increases. The opening-angle dependence should serve as a new means of obtaining information about the pion source in the analysis of experimental data.

We show a practical way based on the Källén-Lehmann representation for the two-point functions to eliminate the instability of the vacuum against formation of small sized meson configurations in the chiral σ model.

The nonrelativistic baryon gas of ${\mathrm{QCD}}_{1+1}$ for SU(2) color is studied in the low density regime using two complementary approaches: In the classical limit, the Gibbs free energy can be evaluated analytically, yielding an exact value for the second virial coefficient and a bound for the equation of state at higher densities. Certain thermodynamic observables can already be given for the entire range of densities due to simple scaling properties. On the other hand, a quantum mechanical baryon-baryon scattering calculation yields the behavior of the second virial coefficient away from the classical limit down to low temperatures.

A model combining vector meson dominance, ω-φ mixing, and a kaon cloud contribution is used to estimate the strangeness vector form factors of the nucleon in the momentum range of the planned measurements at MIT-Bates and CEBAF. We compare our results with some other theoretical estimates and discuss the nucleon strangeness radius in models based on dynamically dressed, extended constituent quarks. For a quantitative estimate in the latter framework we use the Nambu–Jona-Lasinio model.

Weak perturbations can be strongly enhanced in many-body systems that have dense spectra of excited states (compound nuclei, rare-earth atoms, molecules, clusters, quantum dots, etc.). Statistical consideration shows that in the case of zero-width states the probability distribution for the effect of the perturbation has an infinitte variance and does not obey the standard central limit theorem, i.e., the probability density for the average effect X=1/n ${\mathit{tsum}}_{\mathit{i}=1\mathrm{}}^{\mathit{n}}$${\mathit{x}}_{\mathit{i}}$ does not tend to a Gaussian (normal) distribution with variance ${\mathrm{\sigma }}_{\mathit{n}}$=${\mathrm{\sigma }}_1$/ √n , where n is the ‘‘number of measurements.’’ Since for probability densities of this form [f(x)≃a/${\mathit{x}}^2$ at large x] the central limit theorem is ${\mathit{F}}_{\mathit{n}}$(X)=a/${\mathit{X}}^2$+${\mathrm{\pi }}^2$${\mathit{a}}^2$ at n≫1, the breadth of the distribution does not decrease with the increase of n. This means the following. (1) In spite of the random signs of observable effects for different compound states the probability of finding a large average effect for n levels is the same as that for a single-resonance measurements. (2) In some cases one does not need to resolve individual compound resonances and the enhanced value of the effect can be observed in the integral spectrum. This substantially increases the chances to observe statistical enhancement of weak perturbations in different reactions and systems. (3) The average value of parity and time-nonconserving effects in low-energy nucleon scattering cannot be described by a smooth weak optical potential. This ‘‘potential’’ would randomly fluctuate as a function of energy, with typical magnitudes much larger than the nucleon-nucleus weak potential. The effect of finite compound-state widths is considered.

We present a self-consistent analysis of SU(2)-isospin symmetry breakdown in nuclei. We derive the energy difference of nearby nuclei (Z and Z-1) with the same A and splitting in the dispersion relations of protons and neutrons and show that the isobaric analog state is the massive Goldstone boson associated with the isospin polarization of the vacuum. The key relation in this analysis is the partially conserving isobaric current relation (PCIC); this is analogous to the PCAC relation with pion being the massive Goldstone boson.

It is investigated whether or not the direct URCA process proceeds in neutron-star matter with kaon condensation, in connection with potential contribution of the nuclear symmetry energy. We find a region in density-symmetry-energy plane in a model-independent way, where the direct URCA process occurs as a unique rapid cooling process in the kaon condensed phase. Symmetry energies with moderate density dependence pass through this region.

${}_{}{}^{157}{}_{}{}^{}\mathrm{Yb}$ has been produced by irradiation of ${}_{}{}^{147}{}_{}{}^{}\mathrm{Sm}$ with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and studied using a He-jet recoil tape transport system. A decay scheme is proposed for the first time, based on x-γ and γ-γ coincidence measurements, which takes account of 25 observed γ rays.

Mass distribution for reaction products and evaporation residues from the compound nucleus ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$ formed by the ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$${+}^{11}$B reaction at ${\mathit{E}}_{\mathrm{lab}}$=110 MeV has been measured. The saturation value obtained for the critical angular momentum for fusion is consistent with the limit predicted by the rotating liquid drop model with diffuse-surface and finite-nuclear-range corrections. As in the case of the ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$${+}^{10}$B and ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$${+}^9$Be reactions, the disappearance of nuclear structure effects in the sequential decay of the compound nucleus is observed.

The technique of resonant particle decay spectroscopy is used to show that states selectively excited in the three particle transfer reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^7$Li,α${)}^{15}$N have significantly large alpha-particle decay widths. These results imply that simple t${/}^3$He and alpha-particle cluster models will not explain the rather simple spectra observed in three particle transfer reactions. New spectroscopic information on highly excited states in ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ is presented.

The effects of octupole correlations in the Z=63 nuclei ${}_{}{}^{148\mathrm{-}151}{}_{}{}^{}\mathrm{Eu}$ are studied. The persistency of octupole instability through the transitional region of near-spherical (N≤85) towards prolate nuclei (N≥88) is established and discussed. Intrinsic dipole moments, which are experimentally inferred from the measured electric dipole transition rates observed between parity doublets, are used to characterize the strength of the octupole correlations.

An analytic extension of the nuclear algebraic potential in the complex energy and angular momentum planes is discussed and an approximation for the algebraic potential in agreement with the known analytic properties of the S-matrix is proposed. The invariance of the energy spectrum of the Coulomb part of the interaction is established. The results are applied to the Regge pole analysis of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{24}$Mg elastic collision at ${\mathit{E}}_{\mathit{l}\mathit{a}\mathit{b}}$=23.0 MeV.

We calculate the lowest-order contribution to the cross section for simultaneous excitation of projectile and target nuclei in relativistic heavy ion collisions. This process is, to leading order, nonclassical and adds incoherently to the well-studied semiclassical Weizsäcker-Williams cross section. While the leading contribution to the cross section is down by only 1/${\mathit{Z}}_{\mathit{P}}$ from the semiclassical process, and consequently of potential importance for understanding data from light projectiles, we find that phase space considerations render the cross section utterly negligible.

The properties of finite nuclei are studied in a relativistic effective interaction approach. Density dependent coupling constants of the meson-nucleon interactions are adopted to incorporate the Dirac Brueckner-Hartree-Fock (DBHF) results in the relativistic mean field (RMF) or relativistic Hartree-Fock (RHF) approach. It is desired to remedy the deficiencies of the RMF and RHF without losing the features of the relativistic G matrix and at the same time retain the simplicity. The importance of the nucleon correlations, which are expressed by density-dependent coupling constants, is studied and the contribution of isovector mesons is discussed. It is shown that the calculated ground state properties with the density-dependent coupling constants are in good agreement with experiment.

We find that ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${+}^{27}$Al elastic scattering data analyzed by Brandan et al. [Phys. Rev. C 48, 1147 (1993)] are not sufficiently accurate to support their conclusion that the regions of sensitivity where the potential is well determined ‘‘are different for the real and imaginary parts and vary with energy.’’

An enhanced-deformation (ED) rotational band with unusual characteristics has been discovered in the odd-Z nucleus ${}_{}{}^{131}{}_{}{}^{}\mathrm{Pr}$. The dynamical moment of inertia ${\mathcal{J}}^{\mathrm{}\left(2\right)\mathrm{}}$=(50–60)${\mathrm{ħ}}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$ and the extracted quadrupole moment ${\mathit{Q}}_0$ = 5.5 ± 0.8 eb (${\mathrm{\beta }}_2$=0.32±0.05) are comparable with other ED bands (sometimes called ‘‘superdeformed’’) in the mass A∼130 region. The two signature partners of the ED band are connected by dipole transitions which can be followed down to a K=9/2 bandhead. The nature of this band differs from all other ED bands in the A∼130 region since the ${\mathit{i}}_{13/2}$ intruder neutron orbital is unoccupied.