Investigating the dark photon dark matter through an oscillating dilaton

Abstract

A novel mechanism is introduced for the generation of ultralight dark photon dark matter in the early stages of the Universe using a dilatonlike scalar field, which is coupled to the kinetic term of the dark photon. In this framework, energy is primarily contained in the dilaton’s condensate. As this condensate begins its oscillatory motion during the Universe’s early stages, it resonantly produces dark photons. Distinct from axion-dark-photon coupling scenarios that necessitate large coupling coefficients to saturate the dark photon, the dila tonic coupling in our model exhibits a special condition where the dark photon’s mass is half of the dilaton’s. In this regime, significant dark photon production is achievable even with minimal dilaton oscillations. this model, compatible with cosmic microwave background observations, opens the door to ultralight vector dark matter candidates, potentially having masses as minuscule as 10−20 eV