Rare radiative charm decays within the standard model and beyond

Abstract

We present standard model (SM) estimates for exclusive c → uγ processes in heavy quark and hybrid frameworks. Measured branching ratios ℬ(D0→(ϕK¯∗0)γ) are at or somewhat exceeding the upper range of the SM and suggest slow convergence of the 1/mD, αs-expansion. Model-independent constraints on |ΔC| = | ΔU | = 1 dipole operators from ℬ(D0 → ρ0γ) data are obtained. Predictions and implications for leptoquark models are worked out. While branching ratios are SM-like CP asymmetries ≲ 10% can be induced. In SUSY deviations from the SM can be even larger with CP asymmetries of O(0.1). If Λc-baryons are produced polarized, such as at the Z-pole, an angular asymmetry in Λc → pγ decays can be studied that is sensitive to chirality-flipped contributions.