Cosmic coincidence or graviton mass?
  Using the quantum corrected Friedmann equation, obtained from the quantum Raychudhuri equation, and assuming a small mass of the graviton (but consistent with observations and theory), we propose a resolution of the smallness problem(why is observed vacuum energy so small?) and the coincidence problem(why does it constitute most of the universe, about 70%, in the current epoch?). 
Saurya Das
gr-qc astro-ph.CO hep-th