g_A from Lattice QCD 

Following a short overview of the lattice QCD calculations of
isovector charges of the nucleon, I will present results for
isovector g_A=1.218(25)(30) obtained by the PNDME collaboration using
eleven 2+1+1-flavor HISQ ensembles generated by the MILC
collaboration.  The talk will cover details of the control over
excited state contamination and the the chiral-continuum-finite
volume fits leading to the final results. A careful comparison will
be made with recent CalLat result g_A=1.271(13). We show that the
difference comes from the chiral and continuum extrapolation: CalLat
data on the two physical mass ensembles have large errors and do not
contribute significantly to the fits, i.e., their estimate is
essentially based on fits to data with Mπ ≥ 220 MeV, and they have
not simulated the fine a = 0.57 fm ensembles that pull down our
estimate. Our conclusion is that more work is needed to understand
and resolve the systematics at the percent level.