Nonrelativistic QCD for coloured scalars

por Pedro D. Ruiz Femenia (Max-Planck-Institut fur Physik Muenchen)

viernes 28 oct. 2005 12:00 → 13:00 Europe/Madrid

Sala Seminarios IFIC (Edf. Institutos de Investigación)

It is a special feature of pair production of heavy coloured particles close to threshold that multi-gluon exchange leads to singular terms ~(alpha_s/v)^n and ~(alpha_s Log v)^n in the amplitude that for v~alpha_s have to be summed to all orders in alpha_s. This is achieved most efficiently within an effective field theory. For top pair threshold production the effective theory vNRQCD (velocity non-relativistic QCD) was developed to carry out this summation program aiming for NNLL order precision. For squark-antisquark pair threshold production previous studies involved leading-logarithmic (LL) precision. Higher order QCD or electroweak effects were not taken into account in a systematic manner, although it is known from the top threshold that corrections to the LL approximation can be substantial. In this talk I will present the vNRQCD Lagrangian for a particle-antiparticle pair of heavy non-relativistic colored scalars. The matching conditions and anomalous dimensions required for renormalization group improved computations of threshold pair production at next-to-leading logarithmic (NLL) order and scalar-antiscalar bound state energies at NNLL order in the non-relativistic expansion will also be presented. The proposed EFT framework suffices to describe threshold production of squarks in e^+e^- annihilation, in particular of the lighter scalar top quark at the future Linear Collider.