New Physics Effects in Doubly Cabibbo Suppressed D Decays

TL;DR

This paper investigates the potential impact of New Physics on doubly Cabibbo suppressed D decays, challenging the assumption that such decays are unaffected by New Physics and CP violation, through model-specific and model-independent analyses.

Contribution

It provides a comprehensive analysis of New Physics effects in D decays, showing that most models predict small contributions, but identifies a case with significant CP violation possibility.

Findings

New Physics contributions are generally small compared to the Standard Model in most models.

Many constraints are model-independent, strengthening the robustness of the results.

A specific scenario allows for a CP violation contribution of up to 30%.

Abstract

The most sensitive experimental searches for $D-\bar D$ mixing use $D^0 \to K^+ \pi^-$ decays. It is often assumed that effects of New Physics and, in particular, CP violation, can appear through the mixing, while the $c \to d u \bar s$ decay amplitude cannot have significant contributions from New Physics and is, therefore, CP conserving to a good approximation. We examine this assumption in two ways. First, we calculate the contributions to the decay in various relevant models of New Physics: Supersymmetry without R-parity, multi-scalar models, left-right symmetric models, and models with extra quarks. We find that phenomenological constraints imply that the New Physics contributions are indeed small compared to the standard model doubly Cabibbo suppressed amplitude. Second, we show that many of our constraints hold model-independently. We find, however, one case where the model-independent bound is rather weak and a CP violating contribution of order 30% is not excluded.