Recent Astrophysics Results from ORELA and Possible Future Experiments at ORELA and SNS

I present some recent results from experiments at the Oak Ridge Electron Linear Accelerator (ORELA) and discuss their impact in nuclear astrophysics. I then describe some possible future nuclear astrophysics experiments at ORELA and at the Spallation Neutron Source (SNS) being built in Oak Ridge. The SNS and ORELA are complementary, world-class facilities and both will be needed for important future experiments in nuclear astrophysics.Comment: 10 pages, 1 figure, 1 table. To be published in the proceedings of the Workshop on Astrophysics, Symmetries, and Applied Physics at Spallation Neutron Sources, Oak Ridge National Laboratory, March 200

Reduced neutron widths in the nuclear data ensemble: Experiment and theory do not agree

I have analyzed reduced neutron widths ({\Gamma}_{n}^0) for the subset of 1245 resonances in the nuclear data ensemble (NDE) for which they have been reported. Random matrix theory (RMT) predicts for the Gaussian orthogonal ensemble (GOE) that these widths should follow a \c{hi}^2 distribution having one degree of freedom ({\nu}=1) - the Porter Thomas distribution (PTD). Careful analysis of the {\Gamma}_{n}^2 values in the NDE rejects the validity of the PTD with a statistical significance of at least 99.97% ({\nu}=0.801\pm0.052). This striking disagreement with the RMT prediction is most likely due to the inclusion of significant p-wave contamination to the supposedly pure s-wave NDE. When an energy dependent threshold is used to remove the p-wave contamination, the PTD is still rejected with a statistical significance of at least 98.17% ({\nu}=1.217\pm0.092). Furthermore, examination of the primary references for the NDE reveals that many resonances in most of the individual data sets were selected using methods derived from RMT. Therefore, using the full NDE data set to test RMT predictions seems highly questionable. These results cast very serious doubt on claims that the NDE represents a striking confirmation of RMT.Comment: Accepted for publication in Phys. Rev.

Analyzing epsilon'/epsilon in the 1/N_c Expansion

We present a recent analysis of epsilon'/epsilon in the 1/N_c expansion. We show that the 1/N_c corrections to the matrix element of Q_6 are large and positive, indicating a Delta I=1/2 enhancement similar to the one of Q_1 and Q_2 which dominate the CP conserving amplitude. This enhances the CP ratio and can bring the standard model prediction close to the measured value for central values of the parameters.Comment: One reference corrected. 5 pages, talk presented by P.H. Soldan at the 3. International Conference on B Physics and CP Violation, Taipei, Taiwan, December 3 - 7, 1999. Slightly expanded version of the article submitted to the proceeding

Mantle formation, coagulation and the origin of cloud/core-shine: II. Comparison with observations

Many dense interstellar clouds are observable in emission in the near-IR, commonly referred to as "Cloudshine", and in the mid-IR, the so-called "Coreshine". These C-shine observations have usually been explained with grain growth but no model has yet been able to self-consistently explain the dust spectral energy distribution from the near-IR to the submm. We want to demonstrate the ability of our new core/mantle evolutionary dust model THEMIS (The Heterogeneous dust Evolution Model at the IaS), which has been shown to be valid in the far-IR and submm, to reproduce the C-shine observations. Our starting point is a physically motivated core/mantle dust model. It consists of 3 dust populations: small aromatic-rich carbon grains; bigger core/mantle grains with mantles of aromatic-rich carbon and cores either made of amorphous aliphatic-rich carbon or amorphous silicate. We assume an evolutionary path where these grains, when entering denser regions, may first form a second aliphatic-rich carbon mantle (coagulation of small grains, accretion of carbon from the gas phase), second coagulate together to form large aggregates, and third accrete gas phase molecules coating them with an ice mantle. To compute the corresponding dust emission and scattering, we use a 3D Monte-Carlo radiative transfer code. We show that our global evolutionary dust modelling approach THEMIS allows us to reproduce C-shine observations towards dense starless clouds. Dust scattering and emission is most sensitive to the cloud central density and to the steepness of the cloud density profile. Varying these two parameters leads to changes, which are stronger in the near-IR, in both the C-shine intensity and profile. With a combination of aliphatic-rich mantle formation and low-level coagulation into aggregates, we can self-consistently explain the observed C-shine and far-IR/submm emission towards dense starless clouds.Comment: Paper accepted for publication in A&A with companion paper "Mantle formation, coagulation and the origin of cloud/core-shine: I. Dust scattering and absorption in the IR", A.P Jones, M. Koehler, N. Ysard, E. Dartois, M. Godard, L. Gavila