  Nowadays cosmological inflation is the most accepted mechanism to explain the
primordial seeds that led to the structure formation observed in the Universe.
Current observations are in well agreement to initial adiabatic conditions,
which imply that single-scalar-field inflation may be enough to describe the
early Universe. However, there are several scenarios where the existence of
more than a single field could be relevant during this period, for instance,
the situation where the so-called spectator is present. Within the spectator
scenario we can find the possibility that an ultra-light scalar field dark
matter candidate could coexist with the inflaton. In this work we study this
possibility where the additional scalar field could be massive or
self-interacting. We use isocurvature observations to constrain the free
parameters of the model.
