Top Yukawa Coupling Deviations in Muon Colliders

Top Yukawa coupling is deeply connected to many fundamental puzzles in Higgs and Electroweak physics. In this study, we seek to measure the Top Yukawa coupling at the future high-energy muon colliders utilizing the Higgs unitarization in the V_LV_L → tt^* process. If the Top Yukawa coupling deviates from the Standard Model (SM) value, the amplitude of the processes with gauge bosons and top quarks V V → tt^* will increase and deviate from the SM rate as a function of the tt^* center of mass energy. Using this method, we do not need to produce on-shell Higgs boson but indirectly probe its coupling to the top quark. We show that using a muon collider with 10TeV energy and 10ab^-1 integrated luminosity, the collider can probe the Top Yukawa with a precision better than 1.5%. This is a significant improvement from the projected high-luminosity LHC (HL-LHC) limit of 3.2% and the tt^*H process sensitivity at muon colliders.