Searching for New physics in Charm Radiative decays

Abstract

We show that for a heavy vector-like quark model with a down type isosinglet, branching ratio for $c\to u\gamma$ decay is enhanced by more than $\mathcal{O}(10^2)$ as compared to that in the Standard model when QCD corrections to next-to-leading order are incorporated. In a left-right symmetric model (LRSM) along with a heavy vector-like fermion, enhancement of this order can be achieved at the bare (QCD uncorrected) level itself. We propose that a measurement of the photon polarization could be used to signal the presence of such new physics inspite of the large long distance effects. We find that there is a large region within the allowed parameter space of model with vector-like quark with additional left-right symmetry, where depending on the exact size of the long distance contribution, the photon polarization can be dominantly right-handed.

Comments: 26 pages, 3 figures. Few references added and some typos corrected. Figures 2 and 3 replaced by new figures. Modifications in the text discussing the figures. Conclusions largely unchanged