  We analyze exciton spin dynamics in GaSe under nonresonant circularly
polarized optical pumping with an exciton spin-flip rate-equation model. The
model reproduces polarized time-dependent photoluminescence measurements in
which the initial circular polarization approaches unity even when pumping with
0.15 eV excess energy. At T = 10 K, the exciton spin relaxation exhibits a
biexponential decay with a sub-20 ps and a >500 ps time constants, which are
also reproduced by the rate-equation model assuming distinct spin-relaxation
rates for hot (nonequilibrium) and cold band-edge excitons.
