Inhomogeneous Big Bang Nucleosynthesis and Mutual Ion Diffusion

We present a study of inhomogeneous big bang nucleosynthesis with emphasis on transport phenomena. We combine a hydrodynamic treatment to a nuclear reaction network and compute the light element abundances for a range of inhomogeneity parameters. We find that shortly after annihilation of electron-positron pairs, Thomson scattering on background photons prevents the diffusion of the remaining electrons. Protons and multiply charged ions then tend to diffuse into opposite directions so that no net charge is carried. Ions with Z>1 get enriched in the overdense regions, while protons diffuse out into regions of lower density. This leads to a second burst of nucleosynthesis in the overdense regions at T<20 keV, leading to enhanched destruction of deuterium and lithium. We find a region in the parameter space at 2.1E-10<eta<5.2E-10 where constraints 7Li/H<10^{-9.7} and D/H<10^{-4.4} are satisfied simultaneously.Comment: 9 pages, minor changes to match the PRD versio

The Quark-Hadron Phase Transition, QCD Lattice Calculations and Inhomogeneous Big-Bang Nucleosynthesis

We review recent lattice QCD results for the surface tension at the finite temperature quark-hadron phase transition and discuss their implications on the possible scale of inhomogeneities. In the quenched approximation the average distance between nucleating centers is smaller than the diffusion length of a protron, so that inhomogeneities are washed out by the time nucleosynthesis sets in. Consequently the baryon density fluctuations formed by a QCD phase transition in the early universe cannot significantly affect standard big-bang nucleosynthesis calculations and certainly cannot allow baryons to close the universe. At present lattice results are inconclusive when dynamical fermions are included.Comment: 8 pages, LaTe

The Kuiper Belt and Other Debris Disks

We discuss the current knowledge of the Solar system, focusing on bodies in the outer regions, on the information they provide concerning Solar system formation, and on the possible relationships that may exist between our system and the debris disks of other stars. Beyond the domains of the Terrestrial and giant planets, the comets in the Kuiper belt and the Oort cloud preserve some of our most pristine materials. The Kuiper belt, in particular, is a collisional dust source and a scientific bridge to the dusty "debris disks" observed around many nearby main-sequence stars. Study of the Solar system provides a level of detail that we cannot discern in the distant disks while observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book "Astrophysics in the Next Decade

Cosmological Applications of Gravitational Lensing

The last decade has seen an enormous increase of activity in the field of gravitational lensing, mainly driven by improvements of observational capabilities. I will review the basics of gravitational lens theory, just enough to understand the rest of this contribution, and will then concentrate on several of the main applications in cosmology. Cluster lensing, and weak lensing, will constitute the main part of this review.Comment: 26 pages, including 2 figures (a third figure can be obtained from the author by request) gziped and uuencoded postscript file; to be published in Proceedings of the Laredo Advanced Summer School, Sept. 9

Antimatter Regions in the Early Universe and Big Bang Nucleosynthesis

We have studied big bang nucleosynthesis in the presence of regions of antimatter. Depending on the distance scale of the antimatter region, and thus the epoch of their annihilation, the amount of antimatter in the early universe is constrained by the observed abundances. Small regions, which annihilate after weak freezeout but before nucleosynthesis, lead to a reduction in the 4He yield, because of neutron annihilation. Large regions, which annihilate after nucleosynthesis, lead to an increased 3He yield. Deuterium production is also affected but not as much. The three most important production mechanisms of 3He are 1) photodisintegration of 4He by the annihilation radiation, 2) pbar-4He annihilation, and 3) nbar-4He annihilation by "secondary" antineutrons produced in anti-4He annihilation. Although pbar-4He annihilation produces more 3He than the secondary nbar-4He annihilation, the products of the latter survive later annihilation much better, since they are distributed further away from the annihilation zone.Comment: 15 pages, 9 figures. Minor changes to match the PRD versio

Density fluctuations from the quark-hadron epoch and primordial nucleosynthesis

We present a simple thermodynamic model of the quark-hadron transition in the early universe and use this model to estimate how the size of isothermal baryon number fluctuations which emerge from this epoch depend on the temperature of the transition and other uncertain quantities of the underlying QCD physics. We calculate primordial nucleosynthesis in the presence of these fluctuations and find that ..cap omega.. = 1 in baryons is possible only if the measured abundances of /sup 7/Li and /sup 2/H reflect substantial destruction during the evolution of the galaxy. 29 refs., 7 figs