# Searching for New physics in Charm Radiative decays

## TL;DR

This paper investigates how certain new physics models, including vector-like quarks and left-right symmetry, can significantly enhance charm radiative decay rates and alter photon polarization, providing potential signals for beyond Standard Model physics.

## Contribution

It demonstrates that specific new physics models can greatly increase the $c\rightarrow u\gamma$ decay rate and predict distinctive photon polarization signatures, even considering long-distance effects.

## Key findings

- Decay rate enhancement over Standard Model predictions
- Potential for right-handed photon polarization signals
- Parameter space regions with observable effects

## Abstract

We show that for a heavy vector-like quark model with a down type isosinglet, branching ratio for $c\rightarrow u\gamma$ 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.