Electroweak two-loop contribution to the mass splitting within a new heavy SU(2)$_L$ fermion multiplet

TL;DR

This paper calculates the electroweak two-loop contributions to the mass splitting within a heavy SU(2)_L fermion multiplet, revealing that loop corrections induce a non-vanishing mass difference even at large masses.

Contribution

It provides the first detailed two-loop electroweak calculation of mass splitting in heavy fermion multiplets, important for beyond Standard Model physics.

Findings

Two-loop electroweak contributions are typically on the order of MeV.

Mass splitting persists at large multiplet masses due to threshold singularity.

Results refine predictions for mass differences in new heavy fermion multiplets.

Abstract

New heavy particles in an SU(2)_L multiplet, sometimes introduced in extensions of the standard model, have highly degenerate tree-level mass M if their couplings to the Higgs bosons are very small or forbidden. However, loop corrections may generate the gauge-symmetry-breaking mass splitting within the multiplet, which does not vanish in the large M limit due to the threshold singularity. We calculate the electroweak contribution to the mass splitting for a heavy fermion multiplet, to the two-loop order. Numerically, two-loop electroweak contributions are typically O(MeV).