Research Interests

My research is in theoretical high energy physics. I am currently interested in the following areas.

Higher-order QCD corrections

The calculation of higher-order QCD corrections to elementary particle processes is important for the future of high-energy physics. This is because signals of new physics at the new colliders will most likely be weak. Therefore, we need to calculate the predictions of the Standard Model as accurately as possible, in order to maximize the efficiency of future colliders. Unfortunately, higher-order QCD effects are so complicated to calculate that considerable effort is required to obtain manageable expressions. To this end, programming experience as well as analytical skills are needed. There are only a few groups involved in such calculations (e.g., Z. Bern, L. Dixon, et al.). In collaboration with B. F. L. Ward, et al., we have concentrated on the interplay of QCD and electroweak interaction effects. More recently, my students and I have studied the background to an intermediate mass Higgs production at the LHC and the t-tbar production and decay into b-bbar and leptons at the NLC. In both cases, five-point loop diagrams had to be calculated. First, we carefully massaged the amplitudes analytically using helicity amplitudes and exploiting the freedom in choosing reference momenta for the polarization vectors. We then fed the resulting expressions into a symbolic manipulation program (FORM) where appropriate rules had to be defined to further reduce the expressions. The output was then fed to a Monte Carlo event generator which can mimic the specifications of a future collider without any further calculations. In these investigations, we use workstations purchased with DoE funds. We intend to continue with the study of other processes of interest, such as a more general study of t-tbar production, backgrounds to Higgs signals and jet physics.

Supercomputers

The computational work proposed above requires a considerable amount of CPU time. In order to achieve a satisfactory level of accuracy in QCD processes, one needs to generate about 10⁹ events. To realize this in a reasonable amount of time, one needs a parallel arrangement of CPU's. I have therefore started the development of algorithms for parallel machines (supercomputers). During the summer of 1993, Kelly Dowd (an undergraduate student participating in our Science Alliance REU program) and I adapted the prototype code SSCYFS2 to a parallel algorithm for the MasPar MP-2 (with 4096 processors) managed by our Joint Institute for Computing Science. I continued this effort with Xiao Qing Cao, a UTK student, by adapting SSCYFS2 to an algorithm for CM-5 (with 64 processors) at the UTK Computer Science Department. At present, the supercomputers at UTK are not in full use, which ensures adequate access. However, this situation is expected to change gradually, in which case we will have to rely on our workstations. We currently have 3 workstations (a SPARCstation 10/30 and 2 HP9000/735) purchased with Department. To minimize run time, I have linked them to form a virtual parallel machine, by using software which has been developed at UTK and Oak Ridge (PVM). I wish to continue with the development of parallel tools for our system, which will maximize the computational efficiency of the Monte Carlo event generators I shall be developing. As the algorithms become increasingly complicated, this development is imperative for the timely completion of my proposed work. I have also joined other members of our UT in general in a successful bid to NSF for the development of the vBNS network, which will lead to Internet II.

Black holes and string theory

More recently, I have become interested in the rapidly developing field of black holes and dualities, through my student, Marina Shmakova, working with Kallosh, et al. Despite its shortcomings, string theory is still the only viable quantum theory of gravity. A particularly interesting theoretical laboratory for investigations on the problem of information loss, etc, are string super-symmetric black holes. Significant progress was made in understanding those degrees of freedom that give rise to the entropy of certain black holes in string theory. This progress was possible due to the topological nature of the Hawking-Beckenstein entropy of extreme black holes. It was proven that the entropy of a supersymmetric black hole depends only on quantized electric and magnetic charges. One very interesting class of black hole solutions exists in certain supersymmetric theories that can be described by special geometry where one may use the interplay between the geometry of special Kaehler manifolds and space-time geometry. Extreme black holes associated with the most general Calabi-Yau moduli space were investigated. Marina was able to show that the black-hole entropy area law depended on certain combinations of the black-hole charges and the characteristics of the moduli space. These combinations were the solutions of a simple system of algebraic equations. She found explicit solutions for various interesting cases of Calabi-Yau spaces. These results were then confirmed through a microscopic calculation by Witten. We are working on further developing our understanding of super-symmetric black holes in the context of string theory dualities, and M-brane quantization. Such investigations will shed light on a quantum theory of (super)gravity, and perhaps all other forces.