Several recent LHC measurements involving top quarks show an intriguing pattern. Electroweak single-top processes such as $tWZ$ and $tq\gamma$ have been measured somewhat above their Standard Model predictions, while measurements involving a Higgs boson also show interesting shifts. At the same time, closely related multiboson processes remain largely Standard-Model-like.

These observations are not independent: the symmetry of the Standard Model links the interactions of top quarks, Higgs bosons and electroweak gauge bosons. We therefore ask whether these different measurements could reflect a single underlying effect. Using the Effective Field Theory, we find that the data favour a combination of modified top-quark electroweak currents and a weak top dipole interaction, although the current significance is around the $2\sigma$ level.

As this could be very early signs of new physics beyond the Standard Model, it raises the question of what sort of new physics could generate this pattern. Interestingly, no single new particle is sufficient. A possible explanation requires a richer sector of vector-like quarks, with several electroweak representations working together to satisfy precision constraints. The required dipole interaction needs additional loop dynamics. Such a scenario is already within reach of present LHC searches. More precise single-top, $tH$, $ttH$ and vector-like-quark measurements will therefore provide an important test of whether this emerging pattern persists. (Read more)