Exploring charm decays with missing energy in leptoquark models

TL;DR

This paper explores how scalar leptoquarks could influence rare charm hadron decays with missing energy, highlighting potential observable effects at current and future experiments as probes of new physics involving sterile neutrinos.

Contribution

It provides a detailed analysis of leptoquark effects on charm decays with missing energy, considering various models and experimental constraints, and predicts possible branching ratios detectable in upcoming experiments.

Findings

Branching fractions for certain charm decays can reach 10^{-7} to 10^{-6} with R_2 leptoquarks.

ilde R_2 effects are generally smaller than R_2.

ar S_1 leptoquark can induce decay rates up to 10^{-3}, making them accessible to experiments.

Abstract

We investigate the possibility that scalar leptoquarks generate consequential effects on the flavor-changing neutral-current decays of charmed hadrons into final states with missing energy ($\not\!\!E$) carried away by either standard model or sterile neutrinos. We focus on scenarios involving the $R_2$, $\tilde R_2$, and $\bar S_1$ leptoquarks and take into account various pertinent constraints, learning that meson-mixing ones and those inferred from collider searches can be of significance. We find in particular that the branching fractions of charmed meson decays $D\to M\!\not\!\!E$, $M=\pi,\rho$, and $D_s\to K^{(*)}\!\not\!\!E$ and singly charmed baryon decays $\Lambda_c^+\to p\!\not\!\!E$ and $\Xi_c\to\Sigma\!\not\!\!E$ are presently allowed to attain the $10^{-7}$-$10^{-6}$ levels if induced by $R_2$ and that the impact of $\tilde R_2$ is comparatively much less. In contrast, the contributions of $\bar S_1$, which couples to right-handed up-type quarks and the sterile neutrinos, could lead to branching fractions as high as order $10^{-3}$. This suggests that these charmed hadron decays might be within reach of the BESIII and Belle II experiments or future super charm-tau factories and could serve as potentially promising probes of leptoquark interactions with sterile neutrinos.