Appraising constrained second-order power corrections in HQET with $\Lambda_b \to \Lambda_c l \nu$

We derive the $\Lambda_b \to \Lambda_c$ form factors for the Standard Model and beyond at second order in Heavy Quark Effective Theory (HQET), applying the recently-proposed Residual Chiral Expansion (RCE) to reduce the set of unknown subsubleading hadronic functions to a single, highly-constrained function, that is fully determined by hadron mass parameters at zero recoil. We fit a form factor parametrization based on these results to all available Lattice QCD (LQCD) predictions and experimental data. We find that the constrained and predictive structure of the form factors under the RCE is in excellent agreement with LQCD predictions and experimental data, as well as prior HQET-based fits.