Exploring observable effects of scalar operators beyond SMEFT in the angular distribution of $B\to K^{\ast 0}{\tau }^{+}{\tau }^{-}$

The $SU(2{)}_L\times U(1{)}_Y$ invariance of the Standard Model Effective Field Theory (SMEFT) imposes relations among different low-energy effective field theory Wilson coefficients (WCs), any deviations from which would signal the presence of physics beyond SMEFT. In this work, we investigate two such relations ($C_S=-C_P$, $C_S^{\mathrm{\prime }}=C_P^{\mathrm{\prime }}$) among the scalar and the pseudoscalar new-physics WCs that can contribute to $b\to s\tau \tau$ processes. We show that, even when new physics violating these relations would not be measurable in the branching ratios of $B_s\to {\tau }^{+}{\tau }^{-}$ and $B\to K^{(\ast )}{\tau }^{+}{\tau }^{-}$ at HL-LHC and FCC-ee, it can still manifest itself in the angular distribution of $B\to K^{\ast 0}{\tau }^{+}{\tau }^{-}$. We identify the combinations of angular observables in this decay channel that are sensitive to scenarios beyond SMEFT. We find that the two observables $S_6^c$ and $A_7$, and their combination, have the potential to identify physics beyond SMEFT.