Beyond the standard model effective field theory with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>b</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>c</mml:mi><mml:msup><mml:mi>τ</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover></mml:math>

Electroweak interactions assign a central role to the gauge group $SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{Y}$, which is either realized linearly (SMEFT) or nonlinearly (e.g., HEFT) in effective theory obtained when new physics above electroweak scale integrated out. Although discovery of Higgs boson has made SMEFT default assumption, nonlinear realization remains possible. The two can be distinguished through their predictions for size certain low-energy dimension-6 four-fermion operators: these, HEFT predicts $O(1)$ couplings, while they are suppressed by factor ${v}^{2}/{\mathrm{\ensuremath{\Lambda}}}_{\mathrm{NP}}^{2}$, where $v$ vev. One such operator, ${O}_{V}^{LR}\ensuremath{\equiv}(\overline{\ensuremath{\tau}}{\ensuremath{\gamma}}^{\ensuremath{\mu}}{P}_{L}\ensuremath{\nu})(\overline{c}{\ensuremath{\gamma}}_{\ensuremath{\mu}}{P}_{R}b)$, contributes $b\ensuremath{\rightarrow}c{\ensuremath{\tau}}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$. We show that present constraints permit its non-SMEFT coefficient have HEFTy size. also note angular distribution $\overline{B}\ensuremath{\rightarrow}{D}^{*}(\ensuremath{\rightarrow}D{\ensuremath{\pi}}^{\ensuremath{'}}){\ensuremath{\tau}}^{\ensuremath{-}}(\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\tau}}){\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ contains enough information extract coefficients all new-physics operators. Future measurements this therefore tell us if really necessary.