Backreaction of axion coherent oscillations

Understand

We investigate how coherent oscillations backreact on the evolution of the condensate wave function of ultra-light axions in the non-relativistic regime appropriate to cosmic structure formation.

• The coherent oscillations induce higher harmonics beyond the fundamental mode considered so far when a self-interaction is present, and imprint oscillations in the gravitational potential.
• We emphasize that the effective self-interaction felt by the slowly-varying envelop of the wave function always differs from the bare Lagrangian interaction potential.
• We also point out that, in the hydrodynamical formulation of the Gross-Pitaevskii equation, oscillations in the gravitational potential result in an attractive force that counteracts the effect of the quantum pressure arising from the strong delocalization of the particles.