Speaker
Description
I will present a gauge-invariant treatment of longitudinal electroweak radiation in the Herwig 7 angular-ordered electroweak parton shower. In the broken Standard Model, the gauge component of a longitudinal polarisation is related by Ward identities to the corresponding would-be Goldstone mode, so a consistent shower description requires more than a purely subtraction-based prescription. Building on the existing Herwig 7 implementation, we construct a scheme in which the subtraction remainder is completed by the appropriate Goldstone contribution, yielding helicity-resolved quasi-collinear splitting kernels for fermion and vector-boson branchings while leaving the transverse sector unchanged. I will discuss the implementation and its phenomenological consequences in single- and multi-emission studies, highlighting the agreement with the default treatment at high evolution scales and the controlled differences that emerge at lower scales in channels sensitive to electroweak symmetry breaking and fermion masses.