The space-time development of a quark-gluon plasma is calculated from a Vlasov equation for the distribution function of quasiparticles with medium dependent masses. At each space-time point the masses are calculated self-consistently from a gap equation, whose form is determined by the requirement that in thermal equilibrium and for a range of temperatures the energy density of the quasiparticle system is identical to the one from lattice calculations. The numerical solutions of the Vlasov equation display confinement. Relations to effective theories like that by Friedberg and Lee and Nambu and Jona-Lasinio are established.

Direct photon production in central Pb+Pb collisions at CERN-SPS energy is calculated within the ultrarelativistic quantum molecular dynamics model (UrQMD), and within distinctly different versions of relativistic hydrodynamics. We find that in UrQMD the local momentum distributions of the secondaries are strongly elongated along the beam axis initially. Therefore, the pre-equilibrium contribution dominates the photon spectrum at transverse momenta above $\approx 1.5$ GeV. The hydrodynamics prediction of a strong correlation between the temperature and radial expansion velocities on the one hand, and the slope of the transverse momentum distribution of direct photons on the other hand thus is not recovered in UrQMD. The rapidity distribution of direct photons in UrQMD reveals that the initial conditions for the longitudinal expansion of the photon source (the meson “fluid”) resemble boost invariance rather than Landau-like flow.

We analyze the opportunity to observe thermal dileptons emitted off deconfined matter resulting in heavy-ion collisions at RHIC and LHC energies. Special kinematical conditions provided by the detector systems PHENIX and ALICE, and the so-called $M_{\perp }$ scaling behavior of thermal dilepton spectra are taken into account. Our considerations include energy loss effects of the fast heavy quarks in deconfined matter, which for themselves can help to identify the creation of a hot and dense parton medium. Due to a thresholdlike effect for decay leptons we find a window at large transverse pair momentum and fixed transverse mass where the thermal signal can exceed the background of dileptons from correlated semileptonic decays of charm and bottom mesons.

This work investigates the collective motion of kaons in heavy ion reactions at SIS energies (about 1–2 GeV/nucleon). A radial collective flow of $K^{+}$ mesons is predicted to exist in central Au + Au collisions, which manifests in a characteristic “shoulder-arm” shape of the transverse mass spectrum of the midrapidity $K^{+}$ mesons. The $K^{+}$ radial flow arises from the repulsive $K^{+}$ mean field in nuclear matter. In spite of a strong reabsorption and rescattering the attractive $K^{-}$ mean field leads as well to a collective radial flow of $K^{-}$ mesons. The $K^{-}$ radial flow, however, is different from that of $K^{+}$ mesons and can be observed by a characteristic “concave” structure of the transverse mass spectrum of the $K^{-}$ mesons emitted at midrapidity. The kaon radial flows can therefore serve as a novel tool for the investigation of kaon properties in dense nuclear matter.

The transverse momentum distribution of prompt photons coming from the very early phase of ultrarelativistic heavy-ion collisions for the ultrarelativistic energies is calculated by means of perturbative QCD. We calculate the single photon cross section $(A+\overrightarrow{B}\gamma +X)$ by taking into account the partonic subprocesses $q+\overline{q}\to \gamma +g$ and $q+\overrightarrow{g}\gamma +q$ as well as the bremsstrahlung corrections to those processes. We choose a lower momentum cutoff $k_0=2\mathrm{}$ GeV separating the soft physics from perturbative QCD. We compare the results for those primary collisions with the photons produced in reactions of the thermalized secondary particles, which are calculated within scaling hydrodynamics. The QCD processes are taken in leading order. Nuclear shadowing corrections, which alter the involved nuclear structure functions are explicitly taken into account and compared to unshadowed results. Employing the GRV parton distribution parametrizations we find that at ultrarelativistic energies prompt QCD photons dominate over the thermal radiation down to transverse momenta $k_T\approx 2$ GeV. At LHC, however, thermal radiation from the quark-gluon plasma dominates for photon transverse momenta $k_T<~5$ GeV, if nuclear shadowing effects on prompt photon production are taken into account.

Using a Lagrangian which contains quarks as elementary degrees of freedom and mesons as bound states, a transport formalism is developed, which allows for a dynamical transition from a quark plasma to a state, where quarks are bound into hadrons. Simultaneous transport equations for both particle species are derived in a systematic and consistent fashion. For the mesons a formalism is used which introduces off-shell corrections to the off-diagonal Green functions. It is shown that these off-shell corrections lead to the appearance of elastic quark scattering processes in the collision integral. The interference of the processes $q\overline{q}\to \pi$ and $q\overline{q}\to \overrightarrow{\pi }q\overline{q}$ leads to a modification of the $s$-channel amplitude of quark-antiquark scattering.

Using a simple final-state rescattering model coupled with a simple Coulomb model, the effects of the central Coulomb potential on pion interferometry measurements in 158 GeV/nucleon $\mathrm{P}\mathrm{b}+\mathrm{P}\mathrm{b}$ collisions are explored. Although the central Coulomb potential does not introduce correlations between pions, it does prevent an accurate measurement of the momentum difference. This momentum difference smearing effect leads to a reduction in the measured correlation radii and lambda parameters. These distortions are important in 158 GeV/nucleon $\mathrm{P}\mathrm{b}+\mathrm{P}\mathrm{b}$ collisions because of large source sizes and the strong central Coulomb potential.

The production of hadrons in Ni-Ni at the GSI laboratory is considered in a hadronic gas model with chemical equilibrium. Special attention is given to the abundance of strange particles which are treated using the exact conservation of strangeness. It is found that all the data can be described using a temperature $T=70\mathrm{}\pm 10$ MeV and a baryon chemical potential ${\mu }_B=720\mathrm{}\pm 30$ MeV.

Multiparticle symmetrization effects are contributions to the spectra of Bose-symmetrized states which are not the product of pairwise correlations. Usually they are neglected in particle interferometric calculations which aim at determining the geometry of the boson emitting source from the measured momentum distributions. Based on a method introduced by Zajc and Pratt, we give a calculation of all multiparticle symmetrization effects to the one- and two-particle momentum spectra for a Gaussian phase-space distribution of emission points. Our starting point is an ensemble of $N$-particle Bose-symmetrized wave functions with specified phase-space localization. In scenarios typical for relativistic heavy-ion collisions, multiparticle effects steepen the slope of the one-particle spectrum for realistic particle phase-space densities by up to 20 MeV, and they broaden the relative momentum dependence of the two-particle correlations. We discuss these modifications and their consequences in quantitative detail. Also, we explain how multiparticle effects modify the normalization of the two-particle correlator. The resulting normalization conserves event probabilities, which is not the case for the commonly used pair approximation. Finally, we propose a method of calculating Bose-Einstein weights from the output of event generators, taking multiparticle correlations into account.

The mass and wave function of a six-quark system with quantum numbers $J^P{=0\mathrm{}}^{-}$, $T=0\mathrm{}$, called $d^{\prime }$, are calculated. We use a colored diquark-tetraquark cluster model for the six-quark wave function. A constituent quark model Hamiltonian with a two-body confinement potential, and residual one-gluon, one-pion, and one-$\sigma$ exchange interactions is used. The complications due to the quark exchange interactions between tetraquark and diquark clusters (Pauli principle) are taken into account within the framework of the resonating group method. The calculated $d^{\prime }$ mass is some 350 MeV above the empirical value if the same two-body confinement strength as in the nucleon and $\Delta$ is used. This paper also examines the validity of the usual assumption of a universal two-quark confinement strength. We propose that the effective two-body confinement strength in an exotic six-quark system, such as the $d^{\prime }$, could be weaker than in a single baryon. The weaker confinement hypothesis leads to a $d^{\prime }$ mass of $M_{d^{\prime }}=2092\mathrm{}$ MeV and a $d^{\prime }$ radius of $r_{d^{\prime }}=1.53\mathrm{}$ fm.

We study pion-nucleon scattering with a chiral Lagrangian of pions, nucleons, and $\Delta$ isobars. The scattering amplitude is evaluated to one-loop $Q^3$ order, where $Q$ is a generic small momentum, using an approach which is equivalent to heavy baryon chiral perturbation theory. We obtain a good fit to the experimental phase shifts for pion center-of-mass kinetic energies up to 100 MeV. A $\sigma$ term greater than 45 MeV is favored, but the value is not well determined.

We propose a self-consistent approach to the treatment of nuclear matter as a crystal of solitons in the Wigner-Seitz approximation. Specifically, we use a Bloch-like boundary condition on the quarks at the edge of a spherical cell which allows the dispersion relation for a given radius to be calculated self-consistently along with the meson fields; in previous work some ansatz for the dispersion relation has always been an input. Results in all models are very sensitive to the form of the dispersion relation, and so our approach represents a significant advance. We apply the method to both the Friedberg-Lee model and the chiral quark-meson model of Birse and Banerjee. Only the latter shows short-range repulsion; in the former the transition to a quark plasma occurs at unrealistically low densities.

A potential model for four interacting quarks is constructed in SU(2) from six basis states—the three partitions into quark pairs, where the gluon field is either in its ground state or first excited state. With four independent parameters to describe the interactions connecting these basis states, it is possible to fit 100 pieces of data—the ground and first excited states of configurations from six different four-quark geometries calculated on a ${16}^3\times 32$ lattice.

We investigate polarized deuteron structure functions at small values of the Bjorken variable, $x<\mathrm{}0.1\mathrm{}$. In this region contributions from the coherent interaction of diffractively excited hadronic states with both nucleons become important. A proper treatment of this process requires an extension of the Glauber-Gribov multiple-scattering theory to include spin degrees of freedom. In the kinematic domain of current fixed target experiments we observe that shadowing effects in $g_1^d$ are approximately twice as large as for the unpolarized structure function $F_2^d.$ Furthermore at $x<\mathrm{}0.1\mathrm{}$ the tensor structure function $b_1$ is found to receive significant contributions from coherent double scattering.

We study the performance of some recent potential models suggested as effective interactions between constituent quarks. In particular, we address constituent quark models for baryons with hybrid $Q-Q$ interactions stemming from one-gluon plus meson exchanges. Upon recalculating two of such models we find them to fail in describing the $N$ and $\Delta$ spectra. Our calculations are based on accurate solutions of the three-quark systems in both a variational Schrödinger and a rigorous Faddeev approach. It is argued that hybrid $Q-Q$ interactions with a sizable one-gluon-exchange component encounter difficulties in describing baryon spectra due to the specific contributions from one-gluon and meson exchanges together. In contrast, a chiral constituent quark model with a $Q-Q$ interaction relying solely on Goldstone-boson exchange is capable of providing a unified description not only of the $N$ and $\Delta$ spectra but also of all strange baryons in good agreement with phenomenology.

The 56 ton high resolution liquid scintillation calorimeter KARMEN at the beam stop neutrino source ISIS has been used to search for neutrino oscillations in the disappearance channel ${\nu }_e\to {\nu }_x.$ The ${\nu }_e$ emitted in ${\mu }^{+}$ decay at rest are detected with spectroscopic quality via the exclusive charged current reaction ${}^{12}\mathrm{C}({\nu }_e{,e}^{-}{)}^{12}{\mathrm{N}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ almost free of background. Analysis of the spectral shape of $e^{-}$ from the ${\nu }_e$-induced reaction as well as a measurement of the absolute ${\nu }_e$ flux allows one to investigate oscillations of the type ${\nu }_e\to {\nu }_{\tau }$ and ${\nu }_e\to {\nu }_{\mu }.$ The flux-independent ratio $R_{\mathrm{C}\mathrm{C}/\mathrm{N}\mathrm{C}}$ of charged current events ${}^{12}\mathrm{C}({\nu }_e{,e}^{-}{)}^{12}{\mathrm{N}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ to neutral current events ${}^{12}{\mathrm{C}(\mathrm{\nu },\mathrm{\nu }}^{\prime }{)}^{12}{\mathrm{C}}^{*}$ provides additional information in the oscillation channel ${\nu }_e\to {\nu }_x.$ All three analysis methods show no evidence for oscillations. For the ${\nu }_e\to {\nu }_{\tau }$ channel 90% confidence limits of ${\sin }^2\left(2\mathrm{}\Theta \right)<\mathrm{}0.338\mathrm{}$ for $\Delta m^2>~100{\mathrm{eV}}^2{/c}^4$ and $\Delta m^2<0.77\mathrm{}{\mathrm{eV}}^2{/c}^4$ for maximal mixing in a simple two-flavor oscillation formalism are derived. A complete three-flavor analysis of the experimental data from 5 years of measurement with respect to ${\nu }_e\leftrightarrow {\nu }_{\tau }$ and ${\nu }_e\leftrightarrow {\nu }_{\mu }$ mixing is presented.

The recent measurement of the nuclear anapole moment of ${}^{133}$Cs has been interpreted to yield a value of the weak pion-nucleon coupling $H_{\pi }^1$ which contradicts the upper limit from the ${}^{18}$F experiments. We argue that because of the sensitivity of the anapole moment to $H_{\rho }^0$ in the odd proton nucleus ${}^{133}$Cs, there is a combination of weak meson-nucleon couplings which satisfies both experiments and which is (barely) in agreement with theory. In addition, the anapole moment measurement in ${}^{205}$Tl gives a constraint which is inconsistent with the value from ${}^{133}$Cs, calling into question the theory of nuclear anapole moments. We argue that measurements of directional asymmetry in $\overrightarrow{n}+\overrightarrow{p}d+\gamma$ and in the photodisintegration of the deuteron by circularly polarized photons, combined with results from $\mathrm{pp}$ scattering, would determine $H_{\pi }^1$ and several other weak meson-nucleon couplings in a model-independent way.

Parity violating elastic electron-nucleus scattering provides an accurate and model-independent measurement of neutron densities, because the $Z^0$ couples primarily to neutrons. Coulomb distortion corrections to the parity violating asymmetry $A_l$ are calculated exactly using a relativistic optical model. Distortions significantly reduce $A_l$ in a heavy nucleus. However, even with distortions, an experiment to measure the neutron radius is feasible. This will aid the interpretation of future atomic parity violation measurements and provide fundamental nuclear structure information. Coulomb distortions and small differences between neutron and proton radii could be important for a standard model test on ${}^4\mathrm{He}$, ${}^{12}\mathrm{C}$, or ${}^{16}\mathrm{O}$.

Angular distributions of cross section and vector analyzing power have been measured for the ${}^9\mathrm{Be}(\overrightarrow{p}{,d)}^8\mathrm{Be}$ and ${}^9\mathrm{Be}(\overrightarrow{p},\alpha {)}^6\mathrm{Li}$ reactions for $77<~E_p<~321$ keV. Previous work has suggested that that the low-energy cross section is enhanced by the $E_x=6.57\mathrm{}$ MeV subthreshold level in ${}^{10}\mathrm{B}$. The analyzing power measurements are particularly sensitive to the presence of the subthreshold level, leading to a definitive test of the hypothesis. The data are analyzed in terms of $R$-matrix and direct reaction calculations. We find that the magnitude and angular distribution of the ${}^9\mathrm{Be}{\mathrm{}(p,d)\mathrm{}}^8\mathrm{Be}$ reaction at very low energies can be explained by the direct reaction mechanism without any contribution from the subthreshold resonance. The implications of these results for the stellar reaction rate of the ${}^9\mathrm{Be}{\mathrm{}(p,d)\mathrm{}}^8\mathrm{Be}$ and ${}^9\mathrm{Be}(p,\alpha {)}^6\mathrm{Li}$ reactions are discussed.

The equation of state of asymmetric matter including the relativistic exchange and correlation parts is calculated in the σ-ω model. The results are discussed in comparison with empirical informations and phenomenological approaches. Neutron star matter in β equilibrium and the resulting neutron star masses are also discussed.