A New Kind of Weak-Coupling in Top-Quark Physics ?

TL;DR

This paper explores a novel weak-coupling in top-quark decay involving a large chiral transition moment, which introduces a 180-degree phase difference and can be experimentally measured at collider experiments, challenging standard model expectations.

Contribution

It introduces a new type of weak-coupling associated with W-boson energy, providing a potential explanation for observed phase differences in top decay amplitudes and proposing experimental measurement methods.

Findings

Identification of a 180-degree phase difference in top decay amplitudes.

Proposal of measuring this phase via W-boson interference at colliders.

The new coupling maintains unitarity in most high-energy processes.

Abstract

In the standard model, for the t --> W b decay mode, the relative phase is 0-degrees between the dominant A(0,-1/2) and A(-1, -1/2) helicity amplitudes. However, in the case of an additional large t_R --> b_L chiral weak-transition moment, there is instead a 180-degree relative phase and three theoretical numerical puzzles. This phase can be measured at the Tevatron or LHC in top-antitop pair production by use of W-boson longitudinal-transverse interference in beam-referenced stage-two spin-correlation functions. Indeed, this is a new type of weak-coupling for it is directly associated with E_W, the W-boson energy in the top quark rest frame, instead of with a canonical effective mass scale. For most 2 --> 2 reactions, the simple off-shell continuation of this additional coupling is found to have good high energy properties, i.e. it does not destroy 1-loop unitarity of the SM. In a subset of processes, additional third-generation couplings are required.