ULTRA HIGH ENERGY COSMIC RAYS AND DE SITTER VACUA

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.