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OpenLoops 2 Stability System and Parameters

OpenLoops2 supports various methods for the reduction of tensor integrals. In order to avoid potential instabilities at exceptional phase-space points, in particular in IR-singular regions, a sophisticated hybrid double-quadrupole precision system has been developed. This so-called hybrid mode operates exclusively in the in-house on-the-fly reduction, i.e. for all provided one-loop amplitudes apart from the Higgs effective theory and for loop-quared amplitudes.
The hybrid stability system detects potential loss of numerical accuracy via a local numerical error estimation. Open loops which exceed tolerated thresholds are computed in quadruple precision in a separate and independent channel. This quad precision channel is used only for critical parts of the amplitude. The behaviour of this hybrid-precision system can be adjusted based on the following simple switches. For loop-squared amplitudes the OpenLoops 1 stability-system is still in place.

Parameters

Parameter Decription Options
hp_mode select operating modes of hybrid precision system 1: hybrid precision mode for hard regions (default)
2: hybrid precision mode for IR regions
0: hybrid precision mode turned off
hp_loopacc target accuracy in number of correct digits int, default=8