  The production of ultra high-energy cosmic rays in de Sitter invariant vacuum
states is considered. Assuming the present-day universe is asymptoting toward a
future de Sitter phase, we argue the observed flux of cosmic rays places a
bound on the parameter $\alpha$ that characterizes these de Sitter invariant
vacuum states, generalizing earlier work of Starobinsky and Tkachev. If this
bound is saturated, we obtain a new top-down scenario for the production of
super-GZK cosmic rays. The observable predictions bear many similarities to the
previously studied scenario where super-GZK events are produced by decay of
galactic halo super-heavy dark matter particles.
