ABSTRACT

One of the puzzles of the dark energy problem is the ( first ) cosmological coincidence problem , namely , why does our universe begin the accelerated expansion recently ?
why are we living in an epoch in which the dark energy density and the dust matter energy density are comparable ? On the other hand , cosmological observations hint that the equation-of-state parameter ( EoS ) of dark energy crossed the phantom divide w _ { de } = -1 in the near past .
Many dark energy models whose EoS can cross the phantom divide have been proposed .
However , to our knowledge , these models with crossing the phantom divide only provide the possibility that w _ { de } can cross -1 .
They do not answer another question , namely , why crossing the phantom divide occurs recently ? Since in many existing models whose EoS can cross the phantom divide , w _ { de } undulates around -1 randomly , why are we living in an epoch w _ { de } < -1 ? This can be regarded as the second cosmological coincidence problem .
In this work , the cosmological evolution of the vector-like dark energy interacting with background perfect fluid is investigated .
We find that the first and second cosmological coincidence problems can be alleviated at the same time in this scenario .