Phase space factors for double-$\beta$ decay
  A complete and improved calculation of phase space factors (PSF) for $2\nu\beta\beta$ and $0\nu\beta\beta$ decay is presented. The calculation makes use of exact Dirac wave functions with finite nuclear size and electron screening and includes life-times, single and summed electron spectra, and angular electron correlations. 
J. Kotila and F. Iachello
nucl-th