A new B -flavour anomaly in B d,s → K ∗ 0 K ¯ ∗ 0 $$ {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ : anatomy and interpretation

In the context of the recently measured non-leptonic decays Bd → $$ {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ and Bs → $$ {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ we analyse the anatomy of the LVV observable that compares the longitudinal components of Bs → VV and Bd → VV decays. This observable is cleaner than the longitudinal polarisation fraction as it is afflicted only at subleading order in a 1/mb expansion by the theoretical uncertainties arising in the transverse components entering the polarisation fraction. Focusing on the particular case of Bd → $$ {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ and Bs → $$ {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ , we discuss the main sources of hadronic uncertainty in the SM. We find for the SM prediction $$ {L}_{K^{\ast }{\overline{K}}^{\ast }}={19.5}_{-6.8}^{+9.3} $$ , which implies a 2.6σ tension with respect to the most recent data, pointing to a deficit in the b → s transition of the non-leptonic decay versus the corresponding b → d transition. We discuss possible New Physics explanations for this deviation, first at the level of the Weak Effective Theory and we identify that the two Wilson coefficients $$ {\mathcal{C}}_4 $$ and $$ {\mathcal{C}}_{8g} $$ can play a central role in explaining this anomaly. Finally, we briefly explore two different simplified New Physics models which can explain the anomaly through a contribution either in $$ {\mathcal{C}}_4 $$ (Kaluza-Klein gluon) or in $$ {\mathcal{C}}_{8g} $$ , with a significant amount of fine tuning, but possible connections to the b → sll anomalies.