Within the finite-temperature Green’s-function formalism we study the equation of state of a hot interacting pion gas at zero chemical potential. Employing realistic ππ meson-exchange interactions, we self-consistently calculate the in-medium single-pion self-energy and the ππ scattering amplitude in the quasiparticle approximation. These quantities are then used to evaluate the thermodynamic potential ${\mathrm{\Omega }}_{\mathrm{\pi }}$(T) from which the state variables of pressure, entropy, and energy density can be derived. In contrast to earlier calculations based on the low-energy Weinberg Lagrangian we find an overall increase as compared to the free-gas results. We also consider the possibility of a dropping ρ-meson mass as suggested by the ‘‘Brown-Rho scaling’’ law. © 1996 The American Physical Society.

General expressions for transport coefficients of a single-component gas (namely, thermal conductivity and shear and bulk viscosities) of bosons are derived from a Boltzmann-Uehling-Uhlenbeck transport equation by means of the Chapman-Enskog method to first order. These expressions are then used for the calculation of the associated transport relaxation times and applied to the pion gas produced in ultrarelativistic heavy-ion collisions. The influence of Bose enhancement factors on transport properties can be seen by comparison with previous calculations. © 1996 The American Physical Society.

The role of QCD scales and chiral symmetry in finite nuclei is examined. The Dirac-Hartree mean-field coupling constants of Nikolaus, Hoch, and Madland (NHM) are scaled in accordance with the QCD-based prescription of Manohar and Georgi. Whereas the 9 empirically based coupling constants of NHM span 13 orders of magnitude, the scaled coupling constants are almost all natural, being dimensionless numbers of order 1. We argue that this result provides good evidence that QCD and chiral symmetry apply to finite nuclei. © 1996 The American Physical Society.

We study the application of boson mapping methods to a two-color delta model of interacting quarks, with the purpose of extracting information of relevance to quark-model descriptions of nuclei. In an earlier treatment, the boson Hamiltonian resulting from the mapping was approximately diagonalized at the level of Hartree-Bose approximation. The results differed from those of an exact solution of the model at first order in the density. Furthermore, the results were worse than those arising from a BCS treatment of pair correlations at the quark level. Here we extend the analysis to a Brueckner treatment, so as to properly take into account the short-range repulsion between bosons originating from the quark Pauli principle. The resulting energy per quark reproduces the exact results through first order in the density and is significantly better than the BCS results. At higher densities, deviations appear, reflecting the need for a full cluster expansion in the treatment of short-range correlation effects. The relevance of these results to more realistic three-color quark models of nuclei is discussed. © 1996 The American Physical Society.

The main purpose of this work is to estimate to what extent the construction of effective Hamiltonians for pions and nucleons using renormalization group techniques and light-front quantum field theory is worth pursuing. The Hamiltonian we study is obtained from a local theory of fermions coupled to pseudoscalar bosons by making an ad hoc Tamm-Dancoff projection, introducing necessary regularization of divergences, and finding counterterms. We ask if and for what values of the cutoffs and coupling constants the model may be relevant to the physics of pions and nucleons. We calculate the electromagnetic form factors of nucleons and pion-nucleon scattering cross section at small momentum transfers. The model is able to explain the form factor data with accuracy of the order of 30%. The scattering data cannot be explained within the one-boson restriction and seem to require two-boson states. For example, chiral symmetry requires two-boson states. The cutoffs have to be on the order of one to several nucleon masses and the couplings much bigger than 1. We explain the relevance of these results to the program of constructing a light-front Hamiltonian for relativistic pions interacting with nucleons. © 1996 The American Physical Society.

Scaling limits of the structure functions [B.D. Keister, Phys. Rev. C 37, 1765 (1988)], $W_1$ and $W_2$, are studied in a relativistic model of the two-nucleon system. The relativistic model is defined by a unitary representation, $U(\Lambda , a)$, of the Poincaré group which acts on the Hilbert space of two spinless nucleons. The representation is in Dirac's [P.A.M. Dirac, Rev. Mod. Phys. 21, 392 (1949)] light-front formulation of relativistic quantum mechanics and is designed to give the experimental deuteron mass and $n-p$ scattering length. A model hadronic current operator that is conserved and covariant with respect to this representation is used to define the structure tensor. This work is the first step in a relativistic extension of the results of Hueber, Glöckle, and Boemelburg [D. Hueber et al. Phys. Rev. C 42, 2342 (1990)]. The nonrelativistic limit of the model is shown to be consistent with the nonrelativistic model of Hueber, Glöckle, and Boemelburg. The relativistic and nonrelativistic scaling limits, for both Bjorken and $y$ scaling are compared. The interpretation of $y$ scaling in the relativistic model is studied critically. The standard interpretation of $y$ scaling requires a soft wave function which is not realized in this model. The scaling limits in both the relativistic and nonrelativistic case are related to probability distributions associated with the target deuteron.

Neutrino-nucleus cross sections for the detection of atmospheric neutrinos are calculated in relativistic impulse and random phase approximations. Pion production is estimated via inclusive $\Delta$-hole nuclear excitations. The number of pion events can confuse the identification of the neutrino flavor. As a further source of pions we calculate coherent pion production (where the nucleus remains in the ground state). We examine how these nuclear structure effects influence atmospheric neutrino experiments and study possible improvements in the present detector simulations.

Recent (n,p) experiments on ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ have measured Gamow-Teller resonances which are crucial for determining stellar beta decay rates in ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Mn}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Fe}$, respectively. These nuclei are important players in the iron-core URCA process, which is a dynamic balancing of electron capture and beta decay rates during the final stage of nuclear burning in massive stars. We find that three of the nuclei, after calibration from (n,p) measurements, have significantly stronger decay rates than currently expected. These stronger rates will cause a more vigorous URCA process, resulting in presupernova cores which are cooler and less neutron rich than is presently used in core collapse calculations. © 1996 The American Physical Society.

Total fission cross sections of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ projectiles were measured at bombarding energies of 0.6 and 1 GeV per nucleon for seven different targets (Be, C, Al, Cu, In, Au, and U). It is found that all data points fall onto one curve, independent of bombarding energy, once the electromagnetic contribution to the total fission cross sections is subtracted. The abrasion-ablation model predicts a significantly weaker target dependence than observed, and underestimates the nuclear fission cross sections for the heavier targets. © 1996 The American Physical Society.

Analyzing the recent experimental data of Shimoura et al., we show that the dissociation energy spectrum of an intermediate energy ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ nucleus, interacting with a very heavy target, is well reproduced by a direct Coulomb breakup mechanism, provided that in the data the n-n relative energy is subtracted from the dissociation energy. © 1996 The American Physical Society.

The β decay of ${}_{}{}^{94}{}_{}{}^{}\mathrm{Rh}$ is examined theoretically, and it is concluded that this nuclide does not have a $3^{+}$ isomer, as has been proposed, but in fact has almost degenerate $2^{+}$ and $4^{+}$ isomers. Good agreement with experiment is obtained for logft values when these are calculated using N=49 and N=50 wave functions with up to one ${\mathit{g}}_{7/2}$ proton or neutron. © 1996 The American Physical Society.

In the description of deep-inelastic scattering the most extensively used model is the parton model. However, there has been an ongoing effort to understand structure functions of nucleons and mesons in terms of wave functions of quarks. Calculations made using the constituent quark model usually do not fit the experimental data. It has been argued that such calculations refer to some low-momentum scale parameterized by ${\mathit{Q}}_0^2$. The calculated distribution is then evolved up to a large scale, ${\mathit{Q}}^2$, by perturbative QCD evolution. The change needed if the distribution is to fit the data is quite large and, therefore, the scale ${\mathit{Q}}_0^2$ is taken to be quite small. The large changes required for the distribution makes this procedure suspect. In this work we introduce a class of wave functions that are meant to apply at the scale ${\mathit{Q}}^2$, so that evolution is not required. These wave functions describe the motion of a current quark, or parton, relative to a residual system. (In order to calculate a cross section the residual system is placed on mass shell in the calculation.) Our procedure is inherently asymmetric in the description of the struck particle and the residual system. We show how we are able to fit the (valence) structure function of the pion at ${\mathit{Q}}^2$=20 ${\mathrm{GeV}}^2$ (without QCD evolution) using our scheme. © 1996 The American Physical Society.

We present calculations of the quasielastic responses functions in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ based upon a mean-field model used to perform analogous calculations in heavier nuclei. The meson exchange current contribution is small if compared with the results of calculations where short-range correlations are explicitly considered. It is argued that the presence of these correlations in the description of the nuclear wave functions is crucial to make meson exchange current effects appreciable.

Momentum distributions of particles from nuclear breakup of fast three-body halos are calculated consistently, and applied to ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$. The same two-body interactions between the three particles are used to calculate the ground state structure and the final state of the reaction processes. We reproduce the available momentum distributions from ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ fragmentation, together with the size and energy of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$, with a neutron-core relative state containing a p-state admixture of 20%–30%. The available fragmentation data strongly suggest an s state in ${}_{}{}^{10}{}_{}{}^{}\mathrm{Li}$ at about 50 keV and indicate a p state around 500 keV. © 1996 The American Physical Society.

We comment on a recent paper by Bindra et al. [Phys. Rev. C 51, 401 (1995)]. © 1996 The American Physical Society.

We reply to the preceding Comment. © 1996 The American Physical Society.

Two-dimensional pulse height and time-of-flight (TOF) spectra were measured at the IBR-30 pulsed neutron source to make the isotopic identification of the parity-violating $p$-wave resonance at $E_0=3.2\mathrm{}$ eV recently observed in Xe. Analysis of the TOF spectra corresponding to the characteristic low-energy gamma-rays established the ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ isotope as the origin of the 3.2-eV resonance. This new finding poses a challenge for the development of a polarized solid ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ target for a test of time-reversal invariance with neutrons.

A large parity nonconserving longitudinal analyzing power was discovered in polarized-neutron transmission through Xe. An analyzing power of 4.3±0.2% was observed in a $p$-wave resonance at $E_n=3.2\mathrm{}$ eV. The measurement was performed with a liquid Xe target of natural isotopic abundance that was placed in the polarized epithermal neutron beam, flight path 2, at the Manuel Lujan Neutron Science Center. This apparatus was constructed by the TRIPLE Collaboration, and has been used for studies of parity symmetry in compound nuclear resonances. Part of the motivation of the experiment was to discover a nucleus appropriate for a sensitive test of time-reversal invariance in polarized-neutron transmission. The large analyzing power of the observed resonance may make it possible to design a test of time reversal invariance using a polarized-Xe target.

Five bands dominated by strong $M1\mathrm{}$ transitions have been observed in the ${}_{}{}^{136}{}_{}{}^{}\mathrm{Nd}$ nucleus. Two of them consist of only dipole transitions, whereas the other three show also weak crossover transitions. The bands have been firmly connected to lower-spin states. Theoretical calculations using the projected shell model suggest quasiparticle configurations involving two protons and two neutrons for the four lowest-lying bands.

New measurements for lifetimes of excited $0^{+}$ and $2^{+}$ levels in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Xe}$ following $\beta$ decay of ${}_{}{}^{120}{}_{}{}^{}\mathrm{Cs}$ isomers are reported. From these data, $E0\mathrm{}$ and $E2\mathrm{}$ transition rates are derived which exceed values calculated from models assuming only a limited valence nucleon space. The observed collectivity can be described by the inclusion of additional valence protons associated with particle-hole intruder configurations involving the $\pi g_{\frac{9}{2}}$ orbital.