We study the intra-valley spin-orbit mediated spin relaxation in monolayers
of MoS2 within a two bands effective Hamiltonian. The intrinsic spin splitting
of the valence band as well as a Rashba-like coupling due to the breaking of
the out-of-plane inversion symmetry are considered. We show that, in the hole
doped regime, the out-of-plane spin relaxation is not very efficient since the
spin splitting of the valence band tends to stabilize the spin polarization in
this direction. We obtain spin lifetimes larger than nanoseconds, in agreement
with recent valley polarization experiments.Comment: final version, 9 pages, 5 figure