Dark photon is a massive vector field which interacts only with the physical photon through the kinetic mixing .
This coupling is assumed to be weak so that the dark photon becomes almost unobservable in processes with elementary particles , but can serve as a dark matter particle .
We argue that in very early Universe ( z > 3000 ) this vector field may have the equation of state of radiation ( w = 1 / 3 ) but later behaves as cold dark matter ( w = 0 ) .
This may slightly change the expansion rate of the Universe at early time and reduce the value of the sound horizon of baryon acoustic oscillations ( standard ruler ) .
As a result , in this model the value of the Hubble constant appears to be larger than that in the standard \Lambda CDM model .
In particular , it is sufficient to have the dark photon mass of order m \sim 10 ^ { -27 } -10 ^ { -25 } eV to fit the value of the Hubble constant to H _ { 0 } = 73 km s ^ { -1 } Mpc ^ { -1 } thus resolving the Hubble tension .