Higgs production in vector boson fusion at lepton colliders in SMEFT

In this thesis, we describe the first stages of the implementation with GoSam of single Higgs production at a future e^+e^- collider within the framework of Standard Model Effective Field Theory (SMEFT). Studying SMEFT effects at such high energies is crucial to disentangle different new physics footprints or, alternatively, to set robust bounds on them. Our focus will be on Higgs production via vector boson fusion, which becomes increasingly relevant at center-of-mass energies above 300 GeV compared to the Higgstrahlung production channel which, instead, is dominant at low energies. One of the aspects of this thesis is to study the relevance of the interference at leading order between the two production mechanisms, to justify the separate treatments of the two. Up to now, SMEFT effects in vector boson fusion have been investigated only at leading order. However, to fully exploit the discovery potential of a future collider, next-to-leading order electroweak corrections must be included. These corrections not only improve the precision of the predictions, but are also particularly relevant because they become sensitive to operators that do not contribute at leading order. Finally, we discuss the progress that has been achieved in the implementation of the process, together with the validations steps that have been taken so far.