Kaon semileptonic decays with $N_f=2+1+1$ HISQ fermions and physical   light-quark masses
  We discuss the reduction of errors in the calculation of the form factor $f_+^{K \pi}(0)$ with HISQ fermions on the $N_f=2+1+1$ MILC configurations from increased statistics on some key ensembles, new data on ensembles with lattice spacings down to 0.042 fm and the study of finite-volume effects within staggered ChPT. We also study the implications for the unitarity of the CKM matrix in the first row and for current tensions with leptonic determinations of $\vert V_{us}\vert$. 
E. Gamiz, A. Bazavov, C. Bernard, C. DeTar, D. Du, A.X. El-Khadra,   E.D. Freeland, Steven Gottlieb, U.M. Heller, J. Komijan...
hep-lat hep-ex hep-ph