arXiv subjects
Publications and source records attributed to George Siopsis.
We discuss non-relativistic scattering by a Newtonian potential. We show that the gray-body factors associated with scattering by a black hole exhibit the same functional dependence as scattering amplitudes in the Newtonian limit, which should be the weak-field limit of any quantum theory of gravity. This behavior arises independently of the presence of supersymmetry. The connection to two-dimensional conformal field theory is also discussed.
We study the effects of gluon interference in the production and semi-leptonic decay of a t-tbar pair above threshold at the Next Linear Collider (NLC). We calculate all matrix elements to next-to-leading order and use the resulting expressions for the development of a Monte Carlo event generator. Our results show effects at the level of 10% in differential cross-sections. We thus extend previous results obtained by analytical means in the soft-gluon limit.
We discuss non-relativistic scattering by a Newtonian potential. We show that the gray-body factors associated with scattering by a black hole exhibit the same functional dependence as scattering amplitudes in the Newtonian limit, which should be the weak-field limit of any quantum theory of gravity. This behavior arises independently of the presence of supersymmetry. The connection to two-dimensional conformal field theory is also discussed.
We study the effects of gluon interference in the production and semi-leptonic decay of a t-tbar pair above threshold at the Next Linear Collider (NLC). We calculate all matrix elements to next-to-leading order and use the resulting expressions for the development of a Monte Carlo event generator. Our results show effects at the level of 10% in differential cross-sections. We thus extend previous results obtained by analytical means in the soft-gluon limit.
We apply the relativistic Bethe-Salpeter formalism to the calculation of final-state effects in the production of a t-tbar pair at threshold. We find that final-state rescattering does not affect the momentum distribution of the t-tbar pair to lowest order in the strong coupling constant. This result correctly extends earlier results based on the non-relativistic Lippmann-Schwinger equation.
We discuss one-loop electroweak corrections to the decay width of toponium. We calculate the energy-level shifts by expanding around the solution of the Bethe-Salpeter equation in the instantaneous approximation, in analogy with the positronium case. We show that first-order electroweak effects are suppressed by at least four powers of the strong coupling constant, and are therefore negligible compared with QCD corrections. The calculation is manifestly gauge invariant and takes into account the contributions to the decay rate due to both Coulomb enhancement and phase space reduction effects.
We discuss the Hamiltonian formulation of the Schwinger proper-time method of calculating Green functions in gauge theories. Instead of calculating Feynman diagrams, we solve the corresponding Dyson-Schwinger equations. We express the solutions in terms of vertex operators, which consist of the zero modes of the vertex operators appearing in string theories. We show how color decomposition arises in this formalism at tree level. At the one-loop level, we arrive at expressions similar to those obtained in the background gauge. In both cases, no special gauge-fixing procedure is needed.