Computing the $F$-pure Threshold of Flag Varieties

We compute the $F$-pure threshold of the natural cone over flag varieties in characteristic $p>0$. Our calculations are mainly focused on flag varieties that are arithmetically Gorenstein, but we offer some results in the non-Gorenstein case. Our goal is to determine the $a$-invariant of the cone. As a result, the $F$-pure thresholds we find are independent of the characteristic $p$, hence one immediately gets the value of the log canonical threshold of flags in characteristic 0 as well.