  We theoretically investigate the temperature dependence of the reversible
structural relaxation time and diffusion constant of metallic glasses under
pressure. The compression not only changes the glassy dynamics, but also
generates a metastable state along with a higher-energy state where the system
can rejuvenate. The relaxation times for forward and backward transitions in
this two-state system are nearly identical and much faster than the relaxation
time without accounting for barrier-recrossing. At ambient pressure, the
expected irreversible relaxation process is recovered, and our numerical
results agree well with prior experimental results. An increase of pressure has
a minor effect on the relaxation time and diffusion constant that one computes
without considering the influence of the metastable state, but it leads to a
large reduction of the reversible relaxation time computed upon taking the
metastable state into account. The presence of external compression is also
shown to trigger a fragile-to-strong crossover in metallic glasses.
