Towards a viable scalar interpretation of $R_{D^{(*)}}$

TL;DR

This paper explores how simple scalar extensions of the Standard Model can explain anomalies in B-meson decays, showing loop-level effects can mimic vector contributions and remain compatible with collider constraints.

Contribution

It demonstrates that scalar models, including a three-Higgs-doublet framework, can account for $R_{D^{(*)}}$ anomalies through loop effects, challenging the focus on vector-based explanations.

Findings

Scalar extensions can explain $R_{D^{(*)}}$ anomalies via loop corrections.

Simplified scalar models are compatible with collider bounds.

Embedding into three-Higgs-doublet models is phenomenologically viable.

Abstract

Recent measurements of semileptonic B-meson decays seemingly imply violations of lepton flavor universality beyond the Standard Model predictions. With three-level explanations based on extended Higgs sectors being strongly challenged by the measurements of the $B_c^-$ lifetime, new theories invoking leptoquark or vector fields appear as the only feasible answer. However, in this work we show that simple scalar extensions of the Standard Model still offer a possible solution to the $B$ physics puzzle, owing to sizeable loop-level corrections which mimic the effects of new vector contributions. Considering a simplified model characterised by a charged and a neutral scalar particle, we verify the compatibility of the observed $R_{D^{(*)}}$ signal with the relevant collider bounds. We also study an embedding of the simplified model into a three-Higgs-doublet framework, and investigate its main phenomenological constraints.