Ultralight scalars in leptonic observables

Many new physics scenarios contain ultralight scalars, states which are either exactly massless or much lighter than any other massive particle in the model. Axions and majorons constitute well-motivated examples of this type particle. In work, we explore phenomenology these low-energy leptonic observables. After adopting a model independent approach that includes both scalar pseudoscalar interactions, briefly discuss current limits on diagonal couplings to charged leptons consider processes $\phi$ is directly produced, such as $\mu \to e \, \phi$, acts mediator, $\tau \mu \mu$. Contributions magnetic electric moments studied well.