Top-quark electroweak interactions at high energy

Abstract

Modified interactions in the electroweak sector may lead to scattering amplitudes that grow with energy compared to their Standard Model (SM) counterparts. We present a detailed study of all 2 → 2 scattering amplitudes involving at least one top quark and a pair of EW bosons. We analyse the high energy behaviour of the amplitudes using the Standard Model Effective Field Theory (SMEFT) to parametrise the departures from the SM. We discuss the origin of the energy growth that arise from effective contact interactions by appealing to the Goldstone equivalence theorem and find that the amplitudes obey expected patterns of (non-)interference. The results are connected to unitary-violating behaviour in the framework of anomalous SM interactions. Therein, we identify the appearance of additional growth due to the violation of SU(2) gauge symmetry that leads to substantial differences between the SMEFT and the anomalous couplings approaches. We also discuss the embeddings of the scattering amplitudes into physical collider processes, presenting the parametric SMEFT sensitivity to relevant top quark operators and paying special attention to the extent to which the high energy behaviour of the 2 → 2 amplitude is retained in the actual processes accessible at colliders. The effective W approximation is exploited to gain analytical insight into the embeddings of the 2 → 2 helicity amplitudes. Finally, we provide a compendium of processes detailing numerous directions in which the SMEFT parameter space can be accessed through high energy top quark processes in current and future colliders.

Higgs Boson studies at future particle colliders

“…These are of course only a sample of the high-energy precision probes that could be tested at future colliders (and at HL-LHC) so the results presented are not an exhaustive study the potential of the different machines in this regard. (See, e.g., [47,48].) 12 We use an extrapolation of the CLIC results at 380 GeV in [41] to the energy and luminosity of ILC at 500 GeV.…”

O new physics, where art thou? A global search in the top sector

“…Their scaling at high energies depends on the polarization of the Z-boson and has been studied in detail in Refs. [5,46]…”

“…Part of the SMEFT framework [1][2][3][4][5] was developed as a gauge-invariant description of anomalous gauge boson interactions at LEP [6,7]. Its biggest success has been the application to Higgs and electroweak boson measurements at the LHC [8][9][10][11][12][13].…”

Reinterpretation of LHC Results for New Physics: Status and recommendations after Run 2

“…Refs. [162,164]. Moreover, after being evolved to the scale of the b-quark mass, the same SMEFT framework allows for the analysis of the recent data based on B-meson decays that are in tension with the SM predictions.…”