Facility for Rare Isotope Beams

The Cassiopeia A supernova remnant is young, close and bright, allowing unprecedented views of the continuing evolution of the layers from its explosion. Our group has developed a new picture of this explosion using 5-40~micron images and spectra from the Spitzer Space Telescope. In this picture, two roughly spherical shocks (forward and reverse) were initially set up by the outer layers of the exploding star. Deeper layers were ejected in a highly flattened structure with large protrusions in the plane of the flattening; some of these are visible as jets. As these aspherical deeper layers encounter the reverse shock at different locations, they become visible across the electromagnetic spectrum, with different nucleosynthesis layers visible in different directions. In the infrared, we see the gas lines of Ar, Ne, O, Si, S, and Fe at different locations, along with higher ionization states of the same elements visible in the optical and X-ray parts of the spectrum. These different nucleosynthesis layers appear to have formed characteristic types of dust, the deep layers producing dust rich in silicates, while dust from the upper layers is dominated by Al$_2$O$_3$ and carbon grains. In addition, we see circumstellar dust heated by its encounter with the forward shock. We estimate the total dust mass currently visible that was formed in the explosion to be $\sim$0.02-0.05~M$_{\odot}$. Rough extrapolations of these measurements to SNe in high redshift galaxies may be able to account for the lower limit of their observed dust masses. There is a large amount of gas, and presumably dust, that has not yet encountered the reverse shock and is not visible in optical, X-ray, radio and most infrared emission, along with the cooled post-reverse-shock ejecta.

We have recently generalized the Variational Chain Summation method for calculating the equation of state of nucleon matter to finite temperature. After a brief introduction to the zero temperature method, I will discuss the problems associated with its extension to finite temperature and how they can be overcome. Finally I will present some results obtained for hot nucleon matter using this method.

A recent experiment conducted by A. Rouba et al., at Cologne University [1], indicates that a low energy beam of unpolarised deuterons passing through a carbon target, can become tensor polarised in the forward direction. They report a deviation from randomness of approximately 10 per cent. In order to understand this result we investigate the nuclear and atomic scattering of 11.9 MeV deuterons from a ¹²C target. We find that the Coulomb interaction between deuteron and the atomic electrons is dominant over nuclear effects and calculate the tensor polarisation to be three orders of magnitude below the experimental value. If the experimental result is confirmed we are left with a major discrepancy between theory and experiment. {1} A. Rouba et al., Proc. 17th Int. Spin Physics Symp.; SPIN06, 2-7 Oct., Kyoto, Japan, AIP Conf. Proc. 915 (2007).

Understanding the production and distribution of metals in the universe is a major goal of modern astrophysics. While halo stars in our own Milky Way give one view of metal enrichment at early times, the gas in galaxies over a range of redshifts provides another probe of elemental production in galaxies with significantly different star formation histories than the Milky Way. I will describe some of our on-going work to study early nucleosynthesis in galaxies as well as the distribution of metals around galaxies. I will also describe a new approach to studying the primordial lithium abundance.

Estimation of low-energy constants (LECs) is an important component of effective field theory (EFT) programs. For low-energy QCD, a direct calculation of LECs from the underlying theory is possible in only a very few cases, and in practice the LECs are determined by fits to experimental data. There are several questions that need to be considered regarding such a fit: How does one incorporate the information that the LECs are of natural size? At which order in the EFT expansion should the fit be performed? And which data should be used to determine the LECs? We propose a method to address these questions that is based on Bayesian probability theory. The Bayesian framework not only allows for a more stable extraction of parameters from data, but also for a more systematic treatment of uncertainties. To demonstrate our method we present the application to a "toy" problem, as well as a problem in chiral perturbation theory.