One-loop multi-leg calculation in guage theories: Golem library

par Sadek Zidi (LAPTh)

vendredi 6 sept. 2013, 10:00 → 12:00 Europe/Paris

Auditorium Vivargent (Annecy-le-Vieux)

Higher order corrections in gauge theories play a crucial role in studying physics within the standard model and beyond at TeV colliders, like LHC, Tevatron and ILC. Therefore, it is of extreme importance to provide a tool for next-to-leading order amplitude computation fast, stable, efficient in highly automated way. This thesis aims to develop the library of integrals Golem95. This library is a program written in Fortran95, it contains all the necessary ingredients to calculate any one-loop scalar or tonsorial integral with up to six external legs. Golem95 uses the traditional reduction method (reduction à la Golem) which reduces the form factors into redundant basic integrals which can be scalar (without Feynman parameters in the numerator) or tonsorial (with Feynman parameter in the numerator); this formalism allows us to avoid the problems of numerical instabilities generated by the spurious singularities when the Gram determinants (det(G)) vanish. In addition, this library can be interfaced with automatic calculation programs based on the unitarity inspired reduction like GoSam for example. Earlier versions of Golem95 were designed for the calculation of amplitudes without internal masses. Hence, the purpose of my thesis was to extend this library for more general kinematic (complex masses are included); and provide a calculation numerically stable in the problematic regions where det (G) becomes small (or zero).