Does Unruh radiation accelerate the universe? A novel approach to dark   energy
  In braneworld scenario, the brane accelerates in the bulk, and hence it perceives a thermal bulk filled with Unruh radiation. We put forward that there may be an energy exchange between Unruh radiation in the bulk and the dark matter confined to the brane, which accelerates the universe. 
Hongsheng Zhang and Zong-Hong Zhu