Taming the dark photon production via a non-minimal coupling to gravity

Abstract

Inflationary production of massive dark photons with non-minimal couplings to gravity shows surprising growth at large momenta. These couplings appear in the effective low energy description of a more fundamental theory. We find that the growth is absent in explicit gauge invariant UV-complete models. Such completions are also free of "ghost" instabilities, which often appear in the effective models.

Figures (2)

• Figure 1: Generation of the effective $\xi_i$ couplings in UV complete theories. $\phi$ is a scalar and $\tilde{h}_{\mu\nu}$ is a Kaluza-Klein graviton.
• Figure 2: The spectral density of the produced particles as a function of the momentum. In the shaded area, the effective theory breaks down for the parameters of the blue curve ($\xi_1=0.004, \xi_2 =-0.006$), which requires the momentum cutoff $m_A/\sqrt{|\xi_2|} \simeq 0.1 H_e$.