Top Quark Physics at the LHC: top quark pair precision measurements and associated production with additional bosons

The top quark is the heaviest known elementary particle and the only quark that decays before hadronisation, and thus gives direct access to its properties. With its large mass, it plays a crucial role for testing the predictions of the Standard Model (SM) and in the measurement of the Higgs boson properties. Moreover, various scenarios of physics beyond the SM expect the top quark to couple to new particles. The large data samples collected at the CMS and ATLAS experiments at the CERN LHC allow for the first time measuring rare SM processes, challenging the state-of-the-art theoretical predictions and extending the scope of searches for new physics phenomena. This thesis focuses on the study of top quark physics using proton-proton data from both the CMS and ATLAS experiments, collected at centre-of-mass energies of 7, 8 and 13 TeV. In particular, it includes precision measurements related to top quark pair production and the top quark mass, measurements of the associated production of top quark pairs with a Higgs boson, the first direct test of the coupling of the top quark Yukawa coupling, and top quark pair production in association with a photon, which provide the opportunity to directly probe the electroweak couplings of the top quark.