Prospects of discovering new physics in rare charm decays

TL;DR

This paper explores the potential for discovering new physics through rare charm meson decays, analyzing current experimental bounds, and evaluating various new physics models, highlighting leptoquarks as the most impactful.

Contribution

It provides a comprehensive analysis of how existing LHCb bounds constrain new physics contributions in rare charm decays using effective field theory and compares different models' impacts.

Findings

Leptoquark models can significantly alter Wilson coefficients.

Lepton flavor universality may be violated in certain decay channels.

Current bounds restrict the parameter space for new physics in charm decays.

Abstract

The LHCb bounds on the branching ratio of rare decay $D^0 \to \mu^+ \mu^-$ and the constraints on the branching ratio of $D^+ \to \pi^+ \mu^+ \mu^-$ in the nonresonant regions enable us to improve constraints on new physics contributions. Using the effective Lagrangian approach we determine sizes of the Wilson coefficients allowed by the existing LHCb bounds on rare charm decays. Then we discuss contributions to rare charm meson decay observables in several models of new physics: a model with an additional spin-1 weak triplet, leptoquark models, Two Higgs doublets model of type III, and a $Z'$ model. Here we complement the discussion by $D^0 - \bar D^0$ oscillations data. Among considered models, only leptoquarks can significantly modify Wilson coefficients. Assuming that the differential decay width for $D^+ \to \pi^+ \mu^+ \mu^-$ receives NP contribution, while the differential decay width for $D^+ \to \pi^+ e^+ e^-$ is Standard Model-like, we find that lepton flavor universality can be violated and might be observed at high dilepton invariant mass.