A Possible Arena for Searching New Physics - the $\Gamma(D^0 \to \rho^0   \gamma)/\Gamma (D^0 \to \omega \gamma)$ Ratio
  We propose to investigate flavour changing neutral currents in the $c \to u \gamma$ transition through the measurement of the difference between $\Gamma (D^0 \to \rho^0 \gamma)$ and $\Gamma (D^0 \to \omega \gamma)$. This is based on the observation that $D^0 \to (d \bar d) \gamma$ is due to long distance physics while $D^0 \to (u \bar u) \gamma$ arises from the $c \to u \gamma$ transition. The effect of $\rho - \omega$ mixing is included. A difference in the decay widths of more than about 30% would be indicative of new physics. 
S. Fajfer, S. Prelovsek, P. Singer and D. Wyler