Research
My research interests lie chiefly in the field of nuclear and particle astrophysics. In itself, this is quite a broad and diverse field, therefore making it rich and rewarding. Of keen importance, is the fact that across the board, the amount of experimental and observational data is increasing by leaps and bounds. This has transformed nuclear and particle astrophysics from a largely theory-driven field to that driven by data. One can now make quantitative statements about phenomena occurring in the very early universe, or in the extreme environments of exploding stars.
In addition to the large influx of experimental and observational data, computational capabilities have also grown substantially. A tripod (with legs representing experiment, observation and theory), is an unstable structure. It is therefore of the utmost importance to shore up supports that foster and maintain communication between these branches of astrophysics, adding structural integrity to this tripod. I am particularly interested in using experimentally- and/or observationally-constrained theories to describe nature.
My duties of managing the Joint Institute of Nuclear Astrophysics (JINA) NucDataLib and REACLIB Databases and the JINA and SEGUE Virtual Journals help me maintain close ties throughout the community and keep me uptodate on current research. In relation to my research, I have reached across disciplines and can talk with observers, experimentalists and theorists alike. I believe keeping these ties makes my work richer and more fruitful.
My main interest is describing data, whether observationally or experimentally based. This breaks down into two main categories: (1) representing data for use in astrophysical calculations, and (2) performing astrophysical calculations constraining the models through comparisons between predictions and observations.
Nuclear Physics
In my efforts to accurately describe experimental data, I have incrementally added more and more theory into my data representations (or fits). As I have gradually added more theory input to the data descriptions, I have gained much more insight into the reaction problem at hand. To date, I have been able to keep these representations analytic. In the future, I foresee the use of potential, R-matrix models, their hybrids, and shell-model, statistical model and their hybrids.
I have also started a new effort in expanding the theory of the Trojan Horse Method for experimentally accessing low-energy cross-sections otherwise inhibited by difficulties with direct or other indirect methods. I have joined several efforts to establish experimental programs at the ReA3 facility at the NSCL studying the suite of (α,p) reactions important for novae and type I x-ray bursts and using the Pelletron accelerator of the Laborat´orio Aberto de F´isica Nuclear and the HVEC MP Tandem Accelerator in the Laboratrori Nazionali del Sud (LNS) in Catania to study the heavy fusion reactions 12C(12C,α)20Ne, 12C(12C,p)23Na and 12C(12C,n)23Mg.
Big Bang Nucleosynthesis
Currently, standard big bang nucleosynthesis (BBN) is a no-parameter theory (with cosmic microwave background (CMB) anisotropy observations). This theory predicts the abundances of the lightest elements on the chart of nuclides. The concordance between BBN predictions and observations is quite exciting and a fundamental test of the theory. There has been growing evidence of some disagreement between theory predictions and observations. This seemingly persistent discordance lends itself to three explanations. (1) The network of nuclear reactions adopted in BBN calculations is incomplete or one or more rates inaccurate; (2) Stellar evolution changes primordial abundances into those that are observed; and (3) Physics beyond the standard BBN model is affecting the light element abundances. In other words, (1) a nuclear fix, (2) an astrophysics fix, and (3) a new physics fix.
I have spent most of my career addressing fixes (1) and (3). Recent work of mine and my colleagues have just about exhausted all possible nuclear "fixes" to the so-called 7Li problem. New physics scenarios offer two conclusions: (1) there is no difference from standard BBN predictions or (2) all discrepancies can be accounted for, yielding a constrained range for theoretical, new physics parameter values. I would like to spend some time exploring fix (2), the astrophysical (and most likely) fix. To do this, I would need a stellar evolution code. One effort that lends itself to the community is that of MESA, or the Modules for Experiments in Stellar Astrophysics. This suite of codes can be adapted for use in many astrophysics scenarios. I have been working with MESA, in particularly learning how to implement my work with the JINA REACLIB reaction rate database. This would round out all my efforts trying to explain the 7Li problem.
Stellar and Explosive Nucleosynthesis
The 7Li problem is not the only astrophysics problem that can be addressed through stellar/explosive nucleosynthetic codes. With accurate representations of experimental and theoretical reaction rates, I am interested in testing various compilations (old and new) influences on nucleosynthesis codes predictions. I have created and implemented the different formats of the same reaction rate database for use in several astrophysics codes for different scenarios as part of my work with the JINA REACLIB Database. These efforts involve translating data formats that can be read by different astrophysics codes. These comparisons can be used to make the distinction between uncertainties stemming from the nuclear input and those from modelling differences. I have been contributing my expertise from nuclear astrophysics to help create generic explosive nucleosynthesis codes. These codes can then be used to perform sensitivity studies, determining which nuclear reactions or weak decays are most important in particular astrophysics scenarios (e.g. s-, r- and p-processes) and subse- quently garner the most scrutiny in future studies. These studies can then be followed up, evaluating the impact a particular experiment has on astrophysical model predictions.