  Dynamics of the sub-Ohmic spin-boson model under polarized initial conditions
at finite temperature is investigated by employing both analytical tools and
the numerically accurate hierarchical equations of motion-tensor train method.
By analyzing the features of nonequilibrium dynamics, we discovered a
bifurcation phenomenon which separates two regimes of the dynamics. It is found
that before the bifurcation time, increasing temperature slows down the
population dynamics, while the opposite effect occurs after the bifurcation
time. The dynamics is highly sensitive to both initial preparation of the bath
and thermal effects.
