# Looking for New Physics via Semi-leptonic and Leptonic rare decays of $D$ and $D_s$

## TL;DR

This paper investigates rare $D$ and $D_s$ meson decays to search for new physics signals, calculating branching ratios within different models and highlighting potential observable effects at future experiments.

## Contribution

It provides the first detailed calculations of semi-leptonic and leptonic $D$ meson decay rates in $U(1)'$, 2HDM, and unparticle models, identifying potential signals of new physics.

## Key findings

- $U(1)'$ model significantly affects leptonic decay rates.
- Branching ratio of $D^0 o e^- extmu^+$ can reach $10^{-7}$ to $10^{-8}$.
- Future super $ au$-charm factory could observe these rare decays.

## Abstract

It is well recognized that looking for new physics at lower energy colliders is a tendency which is complementary to high energy machines such as LHC. Based on large database of BESIII, we may have a unique opportunity to do a good job. In this paper we calculate the branching ratios of semi-leptonic processes $D^+_s \to K^+ e^-e^+$, $D^+_s \to K^+ e^-\mu^+$ and leptonic processes $D^0 \to e^-e^+$, $D^0 \to e^-\mu^+$ in the frames of $U(1)'$ model, 2HDM and unparticle separately. It is found that both the $U(1)'$ and 2HDM may influence the semi-leptonic decay rates, but only the $U(1)'$ offers substantial contributions to the pure leptonic decays and the resultant branching ratio of $D^0 \to e^-\mu^+$ can be as large as $10^{-7}\sim10^{-8}$ which might be observed at the future super $\tau$-charm factory.