K. K. Sharma and  A. C. Katoch,  Nonfactorizable Contributions to Weak D →ππ
Decay Modes.   journal   = {International Journal of Physical and Mathematical Sciences}, [online]. World Academy of Science, Engineering and Technology.
    December 2012, vol. 72(12). 1635 - 1638
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/10798.