[en] The first step in the study of cosmic strings involves understanding the type of network that forms when the strings are first produced. The universe is treated as a large cube with periodic boundary conditions. The domains that form as Phi approaches the different minima of V are represented by smaller cubes that are stacked into the large one. In each domain, the value of Phi which is approached as the universe cools is chosen at random. A string will form on a domain edge if, when one moves around the four adjacent domain cubes, the corresponding Phi values move completely around the bottom of the Mexican hat. 14 references

[en] The standard big bang model of cosmology is presented. Although not perfect, its many successes make it a good starting point for most discussions of cosmology. Places are indicated where well understood laboratory physics is incorporated into the big bang, leading to successful predictions. Much less established aspects of high energy physics and some of the new ideas they have introduced into the field of cosmology are discussed, such as string theory, inflation and monopoles. 49 refs., 5 figs

[en] I discuss our current understanding of cosmic string evolution, and focus on the question of small scale structure on strings, where most of the disagreements lie. I present a physical picture designed to put the role of the small scale structure into more intuitive terms. In this picture one can see how the small scale structure can feed back in a major way on the overall scaling solution. I also argue that it is easy for small scale numerical errors to feed back in just such a way. The intuitive discussion presented here may form the basis for an analytic treatment of the small structure, which I argue in any case would be extremely valuable in filling the gaps in our resent understanding of cosmic string evolution. 24 refs., 8 figs

[en] I study the quantum mechanics of a spin interacting with an environment. Although the evolution of the whole system is unitary, the spin evolution is not. The system is chosen so that the spin exhibits loss of quantum coherence, or ''wavefunction collapse,'' of the sort usually associated with a quantum measurement. The system is analyzed from the point of view of the spin density matrix (or ''Schmidt path''), and also using the consistent histories (or decoherence functional) approach

[en] A systematic analysis is challenging popular ideas about perturbation from cosmic strings. One way in which the picture has changed is reviewed. It is concluded that, while the scaling properties of cosmic strings figure significantly in the analysis, care must be taken when thinking in terms of single time snapshots. The process of seeding density perturbations is not fundamentally localized in time, and this fact can wash out many of the details which appear in a single snapshot

[en] A discussion of the evolution and observable consequences of a network of cosmic strings is given. A simple model for the evolution of the string network is presented, and related to the statistical mechanics of string networks. The model predicts the long string density throughout the history of the universe from a single parameter, which researchers calculate in radiation era simulations. The statistical mechanics arguments indicate a particular thermal form for the spectrum of loops chopped off the network. Detailed numerical simulations of string networks in expanding backgrounds are performed to test the model. Consequences for large scale structure, the microwave and gravity wave backgrounds, nucleosynthesis and gravitational lensing are calculated

[en] Comments are made on recent claims (Albrecht and Turok, 1989) regarding simulations of cosmic string evolution. Specially, it was claimed that results were dominated by a numerical artifact which rounds out kinks on a scale of the order of the correlation length on the network. This claim was based on an approximate analysis of an interpolation equation which is solved herein. The typical rounding scale is actually less than one fifth of the correlation length, and comparable with other numerical cutoffs. Results confirm previous estimates of numerical uncertainties, and show that the approximations poorly represent the real solutions to the interpolation equation

[en] The constraints on grand unified models required to obtain an inflationary universe scenario are outlined, especially a new assessment of the reheating that follows inflation. The implications for various supersymmetric models are discussed. (orig.)

[en] Cosmological consequences of supersymmetric grand unified models based on the Witten-O'Raifeartaigh potential are discussed. In particular we study the development of the phase transition in the spontaneous breaking of supersymmetry. We find that in realistic models where light fields feel supersymmetry breaking only through coupling to massive fields, e.g., the Geometric Hierarchy model, the universe does not inflate or reheat. Thus, the standard cosmological flatness, monopole, and horizon problems remain. In addition, we find that the transition is never completed, in the sense that the universe remains dominated by coherent Higgs field energy, resulting in an apparent matter dominated universe with Ω greater than or equal to 10³⁰

[en] Based on sediment, water and particle analyses, an investigation of radionuclide distribution was performed in the Gulf of Taranto, a site with two distinctly different sections. Two major rivers transport water and particles from the catchment area into this part of the gulf. Particle concentrations reach a maximum of 3.4 g/m³ in the western part, on the east side and toward the open sea they decrease (∼ 1 g/m³). ⁴⁰K in suspended and deposited particles is higher in the west (1000 Bq/kg) because of higher K concentrations in the source rocks. Activities of ¹³⁷Cs in sediments are also higher in the west (5-10 Bq/kg) than in the east (2-4 Bq/kg). Fluxes, measured in samples with higher activities, remain below 100 Bq m^-2 a^-1 and total sedimentary deposition < 500 Bq m^-2. Deposition of ¹³⁷Cs is considerably lower than known deposition, either caused by atmospheric atomic bomb tests or the Chernobyl accident. This clearly shows the inefficiency of Cs scavenging processes in near coastal systems. Coastal sediments may therefore not allow estimation of ocean discharges by nuclear installations. (author)