  The axial charge of the triton is investigated using lattice quantum
chromodynamics (QCD). Extending previous work at heavier quark masses,
calculations are performed using three ensembles of gauge field configurations
generated with quark masses corresponding to a pion mass of 450 MeV.
Finite-volume energy levels for the triton, as well as for the deuteron and
diproton systems, are extracted from analysis of correlation functions computed
on these ensembles, and the corresponding energies are extrapolated to infinite
volume using finite-volume pionless effective field theory (FVEFT). It is found
with high likelihood that there is a compact bound state with the quantum
numbers of the triton at these quark masses. The axial current matrix elements
are computed using background field techniques on one of the ensembles and
FVEFT is again used to determine the axial charge of the proton and triton. A
simple quark mass extrapolation of these results and earlier calculations at
heavier quark masses leads to a value of the ratio of the triton to proton
axial charges at the physical quark masses of $g_A^{^{3}{\rm
H}}/g_A^p=0.91\substack{+0.07 \\ -0.09}$. This result is consistent with the
ratio determined from experiment and prefers values less than unity (in which
case the triton axial charge would be unmodified from that of the proton),
thereby demonstrating that QCD can explain the modification of the axial charge
of the triton.
