Effects of the Axion Through the Higgs Portal on Primordial Gravitational Waves During the Electroweak Breaking

Understand

We investigate the effects of short axion kination eras on the energy spectrum of the primordial gravitational waves corresponding to modes that re-enter the Hubble horizon at the post-electroweak symmetry breaking epoch, well within the radiation domination era.

• Our main assumption is the existence of an extremely weakly coupled hidden sector between the Higgs and the axion, materialized by higher order non-renormalizable dimension six and dimension eight operators, active at a scale M of the order 20-100TeV.
• This new physics scale M which is way higher than the electroweak scale, is motivated by the lack of new particle observations in the large hadron collider to date, beyond the electroweak scale.
• Once the electroweak symmetry breaking occurs at T\sim 100 GeV, the axion potential acquires a new minimum due to the new terms generated by the electroweak breaking, and the axion oscillations at the origin are destabilized.