Sub-eV scalar dark matter through the super-renormalizable Higgs portal

The Higgs portal of the standard model provides the opportunity for coupling to a very light scalar field φ via the super-renormalizable operator φ(H^H). This allows for the existence of a very light scalar dark matter that has coherent interaction with the standard model particles and yet has its mass protected against radiative corrections. We analyze ensuing constraints from the fifth force measurements, along with the cosmological requirements. We find that the detectable level of the fifth force can be achieved in models with low inflationary scales, and by a certain amount of fine-tuning in the initial deviation of φ from its minimum.