  We argue that one can search for physics beyond the standard model through
measurements of the isospin-violating quantity $\Delta^{-0} \equiv \Gamma(B^-
\to \rho^- \gamma)/2\Gamma(B^0 \to \rho^0 \gamma)-1$, its charge conjugate
$\Delta^{+0}$, and direct CP violation in the partial decay rates of $B^\pm \to
\rho^\pm \gamma$. We illustrate this by working out theoretical profiles of the
charge-conjugate averaged ratio $\Delta \equiv {1 \over 2}(\Delta^{+0}
+\Delta^{-0})$ and the CP asymmetry $A_{CP}(B^\pm \to \rho^\pm \gamma)$ in the
standard model and in some variants of the minimal supersymmetric standard
model. We find that chargino contributions in the large $\tan \beta$ region may
modify the magnitudes and flip the signs of $\Delta$ and $A_{CP}(B^\pm \to
\rho^\pm \gamma)$ compared to their standard-model values, providing an
unmistakeable signature of supersymmetry.

High Energy Physics - Phenomenology