SU(3) breaking in hyperon transition vector form factors

We present a calculation of the SU(3)-breaking corrections to the hyperon transition vector form factors to $\mathcal{O}(p^4)$ in heavy baryon chiral perturbation theory with finite-range regularisation. Both octet and decuplet degrees of freedom are included. We formulate a chiral expansion at the kinematic point $Q^2=-(M_{B_1}-M_{B_2}{)}^2$, which can be conveniently accessed in lattice QCD. The two unknown low-energy constants at this point are constrained by lattice QCD simulation results for the ${\mathrm{\Sigma }}^{-}\to n$ and ${\mathrm{\Xi }}^0\to {\mathrm{\Sigma }}^{+}$ transition form factors. Hence we determine lattice-informed values of $f_1$ at the physical point. This work constitutes progress towards the precise determination of $\mathrm{\mid }{V}_{us}\mathrm{\mid }$ from hyperon semileptonic decays.