Cosmological Constraints on Decoupled Dark Photons and Dark Higgs

TL;DR

This paper investigates how decoupled dark photons and dark Higgs particles, which weakly interact with the Standard Model, are constrained by early universe observations like BBN and CMB, providing new bounds on their properties.

Contribution

It provides new cosmological bounds on dark photon and dark Higgs parameters based on BBN and CMB data, including potential improvements from future experiments.

Findings

Dark photons with kinetic mixing parameter log ε ~ -10 to -17 are constrained for masses 1 MeV to 100 GeV.

Dark Higgs mixing angle log ε ~ -6 to -15 is constrained.

Future experiments like PIXIE could significantly improve these bounds.

Abstract

Any neutral boson such as a dark photon or dark Higgs that is part of a non-standard sector of particles can mix with its standard model counterpart. When very weakly mixed with the Standard Model, these particles are produced in the early Universe via the freeze-in mechanism and subsequently decay back to standard model particles. In this work, we place constraints on such mediator decays by considering bounds from Big Bang nucleosynthesis and the cosmic microwave background radiation. We find both nucleosynthesis and CMB can constrain dark photons with a kinetic mixing parameter between log {\epsilon} ~ -10 to -17 for masses between 1 MeV and 100 GeV. Similarly, the dark Higgs mixing angle {\epsilon} with the Standard Model Higgs is constrained between log {\epsilon} ~ -6 to -15. Dramatic improvement on the bounds from CMB spectral distortions can be achieved with proposed experiments such as PIXIE.