I was reading this interesting article which talks about particle production in an expanding universe.
Usually this process is proposed to have occurred in the early universe, when the expansion was in the inflationary phase and it was so powerful that matter was created in particle production mechanisms.
However, can particles be produced in an accelerating expanding universe like our current one? Can particles be produced by the universe's expansion with the current conditions of our own one?
You get an approach to a finite de Sitter temperature $T=\hbar H/2\pi k_B\approx 2.67\cdot 10^{-30}$ K in a universe expanding forever due to a cosmological constant, and this does produce a very meagre stream of particles as excitations of the fields. So this is something that likely happens in our universe in the standard $\Lambda $CDM cosmology.
This was the hypothesis behind the steady state cosmology. Observations (particularly of the cosmic microwave background) do not agree with its predictions, so it is no longer accepted by most cosmologists.
