Supersymmetric Effects on Isospin Symmetry Breaking and Direct CP Violation in B → ργ

We argue that one can search for physics beyond the standard model through measurements of the isospin-violating quantity ∆ −0 ≡ Γ(B − → ρ − γ)/2Γ(B 0 → ρ 0 γ)−1, its charge conjugate ∆ +0 , and direct CP violation in the partial decay rates of B ± → ρ ± γ. We illustrate this by working out theoretical profiles of the charge-conjugate averaged ratio ∆ ≡ 1 2 (∆ +0 + ∆ −0) and the CP asymmetry A CP (B ± → ρ ± γ) in the standard model and in some variants of the minimal supersymmetric standard model. We find that chargino contributions in the large tan β region may modify the magnitudes and flip the signs of ∆ and A CP (B ± → ρ ± γ) compared to their standard-model values, providing an unmistakeable signature of supersymmetry.