$B\rightarrow K + invisible$ in a model with axion-like particles

TL;DR

This paper updates the theoretical understanding of $B ightarrow K + invisible$ decays involving axion-like particles, highlighting the importance of two-loop contributions and a non-decoupling feature in the minimal UV-complete DFSZ model.

Contribution

It presents two key theoretical updates on the $b o sa$ decay amplitude within the DFSZ model, emphasizing the significance of two-loop diagrams and the non-decoupling phenomenon.

Findings

Two-loop diagrams can dominate one-loop contributions in the decay amplitude.

A non-decoupling feature appears in the light effective theory, indicating incomplete low-energy descriptions.

Renormalizable ALP interactions do not fully capture the observed behavior.

Abstract

The localized excess of $B\rightarrow K + \textit{invisible}$ events reported by Belle-II is commonly interpreted as a signal for $B\to Ka$, where $a$ is an axion-like particle (ALP). In these proceedings, we summarize two theoretical updates regarding the $b\to sa$ decay amplitude within a minimal UV-complete model for invisible ALPs, namely the DFSZ model. (i) Contributions from certain two-loop diagrams can dominate the one-loop ones and are thus relevant for phenomenology. (ii) Although not unique, a rare feature -- which we refer to as apparent non-decoupling -- emerges in the light effective theory. The renormalizable ALP interactions fail to capture this behavior and therefore are incomplete as low-energy effective descriptions.