Unstable-particles pair production in modified perturbation theory in NNLO

TL;DR

This paper develops a modified perturbation theory approach to accurately calculate the pair production and decay of unstable particles at NNLO, demonstrating excellent convergence and minimal discrepancy near the cross-section maximum.

Contribution

It introduces a modified perturbation theory framework for NNLO calculations of unstable particle pair production, with verified high accuracy against exact solutions.

Findings

Excellent convergence of the MPT series near the cross-section maximum

Discrepancy at NNLO is only a few per mille near the maximum

Computations achieve per mille accuracy using FORTRAN code

Abstract

We consider pair production and decay of fundamental unstable particles in the framework of a modified perturbation theory (MPT), which treats resonant contributions of unstable particles in the sense of distributions. The cross-section of the process is calculated within the NNLO of the MPT in a model that admits exact solution. Universal massless-particles contributions are taken into consideration. The calculations are carried out by means of FORTRAN code with double precision, which ensures per mille accuracy of computations. A comparison of the outcomes with the exact solution reveals an excellent convergence of the MPT series at the energies close to and above the maximum of the cross-section. Near the maximum of the cross-section the discrepancy of the NNLO approximation makes up a few per mille.