Relaxion and light (pseudo)scalars at the HL-LHC and lepton colliders

We study the potential of future lepton colliders, running at the Z - pole and above, and the High- Luminosity LHC to search for the relaxion and other light scalars phi. We investigate the interplay of direct searches and precision observables for both CP even and - odd couplings. In particular, precision measurements of exotic Z - decays, Higgs couplings, the exotic Higgs decay into a relaxion pair and associated Z phi and phi gamma production are promising channels to yield strong bounds.