Beam momentum dependence of the experimental cross sections for $p{d}^3\mathrm{H}{\pi }^{+}{/}^3\mathrm{He}{\pi }^0$ reactions have been studied at large proton-pion relative angle. The measurements were performed for five beam momenta in the region of the $\eta$ meson production threshold. Observed behavior of the measured cross sections ratio reveals manifestations of the isospin symmetry breaking effects. A simple model allows one to interpret the isospin symmetry breaking in terms of ${\pi }^0-\eta$ meson mixing. Based on that model analysis of the experimental results leads to the mixing angle value of $0.006\pm 0.005\mathrm{rad}.$

Faddeev calculations are reported for ${}_{\Lambda \Lambda }^5\mathrm{H},$ ${}_{\Lambda \Lambda }^5\mathrm{He},$ and ${}_{\Lambda \Lambda }^6\mathrm{He}$ in terms of two $\Lambda$ hyperons plus ${}^3\mathrm{H},$ ${}^3\mathrm{He},$ and ${}^4\mathrm{He}$ nuclear clusters, respectively, using $\Lambda \Lambda$ central potentials considered in past non-Faddeev calculations of ${}_{\Lambda \Lambda }^6\mathrm{He}.$ The convergence with respect to the partial-wave expansion is studied and comparison is made with some of these $\Lambda \Lambda$ hypernuclear calculations. The $\Lambda \Lambda -\Xi N$ mixing effect is briefly discussed.

A consistent theory of the decay out of superdeformed rotational levels is presented. It is based on exact equations for Green’s functions, taking into account simultaneously both the residual and the electromagnetic interactions. In the weak-coupling limit, we generalized the two-level model of Stafford and Barrett to the case where the superdeformed level is coupled with an infinite equidistant spectrum of normal compound states. For nonoverlapping levels, the general equations of Vigezzi et al. are rederived. The possibility of the nonexponential decay law is discussed.

The fluctuations of the spatial pattern from event to event have been investigated by analyzing the data of multipion production ${\mathrm{in}}^{24}\mathrm{Mg}-\mathrm{AgBr}$ interactions ${\mathrm{and}}^{12}\mathrm{C}-\mathrm{AgBr}$ interactions at $4.5A\mathrm{GeV}$ and ${}^{16}\mathrm{O}-\mathrm{AgBr}$ interactions at $2.1A\mathrm{GeV}$ and $60A\mathrm{GeV}.$ Two entropylike quantities $S_q$ and ${\Sigma }_q$ have been estimated from two different moments of rapidity gaps of produced pions. The investigation provides evidence of the erraticity of rapidity gaps of produced pions in relativistic nuclear collisions.

We perform a realistic study of ${}_{\Lambda }^5\mathrm{He}$ hypernucleus using variational Monte Carlo technique. The Hamiltonian for ${}^4\mathrm{He}$ nuclear core of the hypernucleus is written using Argonne $v_{18}$ $\mathrm{NN}$ potential and Urbana model-IX $\mathrm{NNN}$ potential, where N stands for nucleon. For the strange sector, we use phenomenological $\Lambda N$ potential having central, spin, and exchange components and $\Lambda \mathrm{NN}$ potential which includes spin-dependent dispersive force and two-pion exchange force. Using this Hamiltonian and a fully correlated variational wave function, we reproduce the experimental $\Lambda$ binding energy. Without three-body $\Lambda \mathrm{NN}$ potential in the Hamiltonian and its corresponding correlation in the wave function, the hypernucleus is overbound by 0.56(4) MeV, which is about a quarter of the previous reported values of 2–3 MeV due to the use of central forces. We present the detailed energy breakdown of the hypernucleus and also show the effect of $\Lambda \mathrm{NN}$ correlation on it. The one-body density profiles for nucleon and $\Lambda$ in the hypernucleus and in its nuclear core have been critically examined. The nuclear core polarization due to presence of $\Lambda$ is precisely determined.

The recoil-distance Doppler-shift technique was employed for determining lifetimes of high-spin states in the semimagic nucleus ${}^{93}\mathrm{Tc}.$ The nuclei were populated using the reaction ${}^{64}\mathrm{Zn}{(}^{35}\mathrm{Cl},$ $\alpha 2p)$ at a beam energy of 135 MeV, and the $\gamma$ radiation from their decay was detected in the GASP spectrometer. A total of 26 reduced transition probabilities and limits for 19 further transitions were extracted and compared to large-scale shell model calculations, considering different configuration spaces and residual interactions. The information deduced about transition strengths turned out to be essential for the correct assignment of the calculated to the experimental excited states.

The relativistic mean-field plus random phase and quasiparticle random phase approximation calculations, based on effective Lagrangians with density-dependent meson-nucleon vertex functions, are employed in a microscopic analysis of the nuclear matter compressibility and symmetry energy. We compute the isoscalar monopole response of ${}^{90}\mathrm{Zr},$ ${}^{116}\mathrm{Sn},$ ${}^{144}\mathrm{Sm},$ the isoscalar monopole and isovector dipoles response of ${}^{208}\mathrm{Pb},$ and also the differences between the neutron and proton radii for ${}^{208}\mathrm{Pb}$ and several Sn isotopes. The comparison of the calculated excitation energies with the experimental data on the giant monopole resonances restricts the nuclear matter compression modulus of structure models based on the relativistic mean-field approximation to $K_{\mathrm{nm}}\approx 250–270\mathrm{MeV}.$ The isovector giant dipole resonance in ${}^{208}\mathrm{Pb}$ and the available data on differences between the neutron and proton radii limit the range of the nuclear matter symmetry energy at saturation (volume asymmetry) of these effective interactions to $32\mathrm{MeV}<~a_4<~36\mathrm{MeV}.$

The statistical mechanics of quarks and gluons are investigated within the context of the canonical ensemble. Recursive techniques are developed, which enforce the exact conservation of baryon number, total isospin, electric charge, strangeness, and color. Bose and Fermi-Dirac statistics are also accounted for to all orders. The energy, entropy, and particle number densities are shown to be significantly reduced for volumes less than $5{\mathrm{fm}}^3.$

We calculate the imaginary parts of the isoscalar-scalar and isovector-electromagnetic form factors of the nucleon up to two-loop order in chiral perturbation theory. Particular attention is paid to the correct behavior of $\mathrm{Im}{\sigma }_N\mathrm{}\left(t\right)\mathrm{}$ and $\mathrm{Im}{G}_{E,M}^V\mathrm{}\left(t\right)\mathrm{}$ at the two-pion threshold $t_0{=4m}_{\pi }^2$ in connection with the nonrelativistic $1/M$ expansion. We recover the well-known strong enhancement near threshold originating from the nearby anomalous singularity at $t_c{=4m}_{\pi }^2-m_{\pi }^4{/M}^2{=3.98m}_{\pi }^2.$ In the case of the scalar spectral function $\mathrm{Im}{\sigma }_N\mathrm{}\left(t\right),$ one finds a significant improvement in comparison to the lowest order one-loop result. Higher order ππ-rescattering effects are, however, still necessary to close a remaining 20% gap to the empirical scalar spectral function. The isovector electric and magnetic spectral functions $\mathrm{Im}{G}_{E,M}^V\mathrm{}\left(t\right)\mathrm{}$ get additionally enhanced near threshold by the two-pion-loop contributions. After supplementing their two-loop results by a phenomenological ρ-meson exchange term, one can reproduce the empirical isovector electric and magnetic spectral functions fairly well.

We have measured the nuclear transparency of the fundamental process $\gamma \overrightarrow{n}{\pi }^{-}p$ in ${}^4\mathrm{He}.$ These measurements were performed at Jefferson Lab in the photon energy range of 1.6–4.5 GeV and at ${\theta }_{\mathrm{cm}}^{\pi }=70\mathrm{}°$ and $90°.$ These measurements are the first of their kind in the study of nuclear transparency in photoreactions. They also provide a benchmark test of Glauber calculations based on traditional models of nuclear physics. The transparency results suggest deviations from the traditional nuclear physics picture. The momentum transfer dependence of the measured nuclear transparency is consistent with Glauber calculations that include the quantum chromodynamics phenomenon of color transparency.

For non-Borromean two-neutron halo nuclei, modifications to the behavior of single-particle overlap integrals will arise due to the correlations of the two interacting nucleons in the halo. An additional contribution to the overlap integral can be obtained using the Feynman diagram approach. This additional term is modeled using a simple local potential model. We show that these modifications may play a role in detailed interpretations of experimental results from single-nucleon knockout, transfer, and other reactions that probe the single-nucleon overlap functions.

Isotopic composition of the fragments emitted during the multifragmentation of ${}^{58}\mathrm{Ni}{+}^{58}\mathrm{Ni},$ ${}^{58}\mathrm{Fe}{+}^{58}\mathrm{Ni},$ ${}^{58}\mathrm{Ni}{+}^{58}\mathrm{Fe},$ and ${}^{58}\mathrm{Fe}{+}^{58}\mathrm{Fe}$ was studied at beam energies of 30, 40, and 47 MeV/nucleon. Within the context of a grand-canonical approach, relative free neutron and proton densities, extracted from the measured isotope and isotone yield ratios, suggest that the neutron content of the vapor phase increases with the isospin $\mathrm{}(N/Z)\mathrm{}$ of the initial colliding nuclei and decreases with the beam energy.

A systematic study of isotope chains in the rare-earth region is presented. For chains ${}_{60}^{144-154}\mathrm{Nd},$${}_{62}^{146-160}\mathrm{Sm},$${}_{64}^{148-162}\mathrm{Gd},$ and ${}_{66}^{150-166}\mathrm{Dy},$ energy levels, E2 transition rates, and two-neutron separation energies are described by using the most general (up to two-body terms) interacting boson model (IBM) Hamiltonian. For each isotope chain a general fit is performed in such a way that all parameters but one are kept fixed, to describe the whole chain. In this region, nuclei evolve from spherical to deformed shapes and a method based on catastrophe theory, in combination with a coherent-state analysis to generate the IBM energy surfaces, is used to identify critical phase transition points.

The recently developed auxiliary field diffusion Monte Carlo method is applied to compute the equation of state and the compressibility of neutron matter. By combining diffusion Monte Carlo method for the spatial degrees of freedom and auxiliary field Monte Carlo method to separate the spin-isospin operators, quantum Monte Carlo can be used to simulate the ground state of many-nucleon systems $(A\lesssim 100).$ We use a path constraint to control the fermion sign problem. We have made simulations for realistic interactions, which include tensor and spin-orbit two-body potentials as well as three-nucleon forces. The Argonne $v_8^{\prime }$ and $v_6^{\prime }$ two-nucleon potentials plus the Urbana or Illinois three-nucleon potentials have been used in our calculations. We compare with fermion hypernetted chain results. We report on the results of a periodic box fermi hypernetted chain calculation, which is also used to estimate the finite size corrections to our quantum Monte Carlo simulations. Our auxiliary field diffusion Monte Carlo (AFDMC) results for $v_6$ models of pure neutron matter are in reasonably good agreement with equivalent correlated basis function (CBF) calculations, providing energies per particle which are slightly lower than the CBF ones. However, the inclusion of the spin-orbit force leads to quite different results particularly at relatively high densities. The resulting equation of state from AFDMC calculations is harder than the one from previous Fermi hypernetted chain studies commonly used to determine the neutron star structure.

An inclusive $\alpha$-particle spectrum from the ${}^1\mathrm{H}{(}^6\mathrm{He},\alpha )$ reaction has been measured at a ${}^6\mathrm{He}$ laboratory energy of 23.9 MeV. A resonancelike structure is observed at an $\alpha$-particle lab energy of about 20 MeV, which corresponds to an energy of $E_{\mathrm{nd}}=0.6\mathrm{}\mathrm{MeV}$ in the $n-d$ channel. An analysis of the spectrum shows that it cannot be explained by the effect of binary final-state interactions. The hypotheses that this structure represents (a) a new excited state of tritium or (b) a three-body final-state interaction are discussed.

The $K^{-}{/K}^{+}$ ratio produced in heavy-ion collisions at GSI energies is studied. The in-medium properties at finite temperature of the hadrons involved are included, paying special attention to the in-medium properties of antikaons. Using a statistical approach, it is found that the determination of the temperature and chemical potential at freeze-out conditions compatible with the ratio $K^{-}{/K}^{+}$ is very delicate, and depends very strongly on the approximation adopted for the antikaon self-energy. The use of an energy-dependent $\overline{K}$ spectral density, including both s- and p-wave components of the $\overline{K}N$ interaction, lowers substantially the freeze-out temperature compared to the standard simplified mean-field treatment and gives rise to an overabundance of $K^{-}$ production in the dense and hot medium. Even a moderately attractive antikaon-nucleus potential obtained from our self-consistent many-body calculation does reproduce the “broadband equilibration” advocated by Brown, Rho, and Song due to the additional strength of the spectral function of the $K^{-}$ at low energies.

The eigenstates of a single massless Dirac particle confined in a linear potential are calculated exactly by direct solution of the Dirac equation. The electromagnetic structure functions are calculated from the Dirac wave functions of the ground and excited states of the particle by coupling to its conserved vector current. We obtain the longitudinal and transverse structure functions as a function of $\tilde{y}=\nu -|\mathbf{q}|,$ where $\nu$ and $|\mathbf{q}|$ are the energy and momentum transferred to the target in its rest frame. At values of $|\mathbf{q}|\gtrsim 2.5\mathrm{GeV},$ much larger than the characteristic energy scale $\sim 440\mathrm{MeV}$ of the confining potential, the response exhibits $\tilde{y}$ scaling, a generalization of Bjorken scaling. We compare the exact structure functions with those obtained from the ground state wave functions in the plane wave impulse approximation. The deviation from the Callan-Gross relation is compared with the parton model prediction.

Uniform neutron matter is approximated by a cubical box containing a finite number of neutrons, with periodic boundary conditions. We report variational and Green’s function Monte Carlo calculations of the ground state of fourteen neutrons in a periodic box using the Argonne ${v8\mathrm{}}^{\prime }$ two-nucleon interaction at densities up to one and half times the nuclear matter density. The effects of the finite box size are estimated using variational wave functions together with cluster expansion and chain summation techniques. They are small at subnuclear densities. We discuss the expansion of the energy of low-density neutron gas in powers of its Fermi momentum. This expansion is strongly modified by the large $\mathrm{nn}$ scattering length, and does not begin with the Fermi-gas kinetic energy, as assumed in both Skyrme and relativistic mean field theories. The leading term of neutron gas energy is approximately half the Fermi-gas kinetic energy. The quantum Monte Carlo results are also used to calibrate the accuracy of variational calculations employing Fermi hypernetted and single operator chain summation methods to study nucleon matter over a larger density range, with more realistic Hamiltonians including three-nucleon interactions.

Advances in neutrino transport allow realistic neutrino interactions to be incorporated into supernova simulations. We add tensor couplings to relativistic random phase approximation calculations of neutrino opacities. Our results reproduce free-space neutrino-nucleon cross sections at low density, including weak magnetism and recoil corrections. In addition, our opacities are thermodynamically consistent with relativistic mean field equations of state. We find antineutrino mean free paths that are considerably larger then those for neutrinos. This difference depends little on density. In a supernova, this difference could lead to an average energy of ${\overline{\nu }}_{\mu }$ that is larger than that for ${\nu }_{\mu }$ by an amount that is comparable to the energy difference between ${\nu }_{\mu }$ and ${\overline{\nu }}_e.$