Nonrelativistic effective field theory of unstable top

Abstract

We develop a new nonrelativistic effective field theory of $\rho$NRQCD [1] to describe the finite lifetime effects in the threshold production of top quark-antiquark pairs. The theory is based on the expansion in a parameter $\rho =1-m_W/m_t$ characterizing the dynamics of the top-quark decay. Within this framework we compute the nonresonant contribution to the total cross section of the top quark-antiquark threshold production in electron-positron annihilation up to the next-to-next-to-leading order. Our method naturally resolves the problem of spurious divergences in the analysis of the unstable top production.

Comments: 9 pages, 4 figures, talk given at the conference "Loops and Legs in Quantum Field Theory", Wernigerode, Germany, 15-20 April 2012